Satellite Trunked Radio Service System

This application claims priority from U.S. provisional application serial number 60/003,989 filed on Sep. 19, 1995 entitled "Satellite Trunked Radio Service System," and U.S. provisional application serial number 60/014,205 filed on Mar. 27, 1996 entitled "Improved Satellite Trunked Radio Service System."

The present invention relates generally to a satellite trunked radio service system for satellite communication, and more particularly, to a satellite trunked radio service system for satellite communication utilizing a shared satellite demand period circuit associated with private voice networks.

An overview of the satellite network system is illustrated in FIG. 1. The satellite network system design provides the capability for METs and FESs to access one or more multiple beam satellites located in geostationary orbit to obtain communications services.

The heart of the satellite network system for each of the networks is the Network Control System (NCS) which monitors and controls each of the networks. The principal function of the NCS is to manage the overall satellite network system, to manage access to the satellite network system, to assign satellite circuits to meet the requirements of mobile customers and to provide network management and network administrative and call accounting functions.

The satellites each transmit and receive signals to and from METs at L-band frequencies and to and from Network Communications Controllers (NCCs) and Feederlink Earth Stations (FESs) at Ku-band frequencies. Communications at L-band frequencies is via a number of satellite beams which together cover the service area. The satellite beams are sufficiently strong to permit voice and data communications using inexpensive mobile terminals and will provide for frequency reuse of the L-band spectrum through inter-beam isolation. A single beam generally covers the service area.

The satellite network system provides the capability for mobile earth terminals to access one or more multiple beam satellites located in geostationary orbit for the purposes of providing mobile communications services. The satellite network system is desired to provide the following general categories of service:

Mobile Telephone Service (MTS). This service provides point-to-point circuit switched voice connections between mobile and public switched telephone network (PSTN) subscriber stations. It is possible for calls to be originated by either the mobile terminal or terrestrial user. Mobile terminal-to-mobile terminal calls are also supported.

Mobile Radio Service (MRS). This service provides point-to-point circuit switched connections between mobile terminal subscriber stations and subscriber stations in a private network (PN) which is not a part of the PSTN. It is possible for calls to be originated from either end. Mobile terminal-to-mobile terminal calls are also supported.

Mobile Telephone Cellular Roaming Service (MTCRS). This service provides Mobile Telephone Service to mobile subscribers who are also equipped with cellular radio telephones. When the mobile terminal is within range of the cellular system, calls are serviced by the cellular system. When the mobile terminal is not in range of the cellular system, the MTCRS is selected to handle the call and appears to the user to be a part of the cellular system. When the mobile terminal is not in range of the cellular system, the MTCRS is selected to handle the call and appears to the user to be a part of the cellular system. It is possible for calls to be originated either from the MET or the PSTN. Mobile terminal-to-mobile terminal calls are also supported.

Mobile Data Service (MDS). This service provides a packet switched connection between a data terminal equipment (DTE) device at a mobile terminal and a data communications equipment (DCE)/DTE device connected to a public switched packet network. Integrated voice/data operation is also supported.

The satellites are designed to transmit signals at L-band frequencies in the frequency band 1530-1559 MHz. They will receive L-band frequencies in the frequency band 1631.5-1660.5 MHz. Polarization is right hand circular in both bands. The satellites will also transmit in the Ku frequency band, 10,750 MHz to 10,950 MHz, and receive Ku-band signals in the frequency band 13,000 to 13,250 MHz.

The satellite transponders are designed to translate communications signals accessing the satellite at Ku-band frequencies to an L-band frequency in a given beam and vice versa. The translation will be such that there is a one-to-one relation between frequency spectrum at Ku-band and frequency spectrum in any beam at L-band. The satellite transponders will be capable of supporting L-band communications in any portion of the 29 MHz allocation in any beam.

Transponder capacity is also provided for Ku-band uplink to Ku-band down-link for signalling and network management purposes between FESs and NCCs. The aggregate effective isotropic radiated power (AEIRP) is defined as that satellite e.i.r.p. that would result if the total available communications power of the communications subsystem was applied to the beam that covers that part of the service area. Some of the key performance parameters of the satellite are listed in FIG. 2.

The satellite network system interfaces to a number of entities which are required to access it for various purposes. FIG. 3 is a context diagram of the satellite network system illustrating these entities and their respective interfaces. Three major classes of entities are defined as user of communications services, external organizations requiring coordination, and network management system.

The users of satellite network communications services are MET users who access the satellite network system either via terrestrial networks (PSTN, PSDN, or Private Networks) or via METs for the purpose of using the services provided by the system. FES Owner/Operators are those organizations which own and control FESs that provide a terrestrial interface to the satellite network. When an FES becomes a part of the satellite network, it must meet specified technical performance criteria and interact with and accept real-time control from the NCCs. FES Owner/Operators determine the customized services that are offered and are ultimately responsible for the operation and maintenance of the FES. Customers and service providers interact with the Customer Management Information System within the Network Management System.

The satellite network system interfaces to, and performs transactions with, the external organizations described below:

Satellite Operations Center (SOC): The SOC is not included in the satellite network ground segment design. However, the satellite network system interfaces with the SOC in order to maintain cognizance of the availability of satellite resources (e.g. in the event of satellite health problems, eclipse operations, etc.) and, from time to time, to arrange for any necessary satellite reconfiguration to meet changes in traffic requirements.

NOC: The satellite network system interfaces with the satellites located therein via the NOC for a variety of operational reasons including message delivery and coordination.

Independent NOCs: The satellite network system interfaces with outside organizations which lease resources on satellite network satellites and which are responsible for managing and allocating these resources in a manner suited to their own needs.

Other System NOCs: This external entity represents outside organizations which do not lease resources on satellite network satellites but with whom operational coordination is required.

The satellite network management system (NMS) is normally located at an administration's headquarters and may comprise three major functional entities; Customer Management Information System (CMIS), Network Engineering, and System Engineering (NE/SE). These entities perform functions necessary for the management and maintenance of the satellite network system which are closely tied to the way the administration intends to do business. The basic functions which are performed by CMIS, Network Engineering, and System Engineering are as follows:

Customer Management Information System: This entity provides customers and service providers with assistance and information including problem resolution, service changes, and billing/usage data. Customers include individual MET owners and fleet managers of larger corporate customers. Service providers are the retailers and maintenance organizations which interact face to face with individual and corporate customers.

Network Engineering: This entity develops plans and performs analysis in support of the system. Network Engineering analyzes the requirements of the network. It reconciles expected traffic loads with the capability and availability of space and ground resources to produce frequency plans for the different beams within the system. In addition, Network Engineering defines contingency plans for failure situations.

System Engineering: This entity engineers the subsystems, equipment and software which is needed to expand capacity to meet increases in traffic demands and to provide new features and services which become marketable to subscribers.

The satellite network system comprises a number of system elements and their interconnecting communications links as illustrated in FIG. 4. The system elements are the NOC, the NCC, the FES, the MET, the Remote Monitor Station (RMS), and the System Test Station (STS). The interconnecting communications links are the satellite network Internetwork, terrestrial links, the MET signaling channels, the Interstation signaling channels, and the MET-FES communications channels. The major functions of each of the system elements are as follows:

NOC. The NOC manages and controls the resources of the satellite network system and carries out the administrative functions associated with the management of the total satellite network system. The NOC communicates with the various internal and external entities via a local area network (LAN)/wide area network (WAN) based satellite network Internetwork and dial-up lines.

NCC. The NCC manages the real time allocation of circuits between METs and FESs for the purposes of supporting communications. The available circuits are held in circuit pools managed by Group Controllers (GCs) within the NCC. The NCC communicates with the NOC via the satellite network Internetwork, with FESs via Ku-to-Ku band interstation signaling channels or terrestrial links, and with mobile terminals via Ku-to-L band signaling channels.

FES. The FES supports communications links between METs, the PSTN, private networks, and other MTs. Once a channel is established with an MET, call completion and service feature management is accomplished via In-Band signaling over the communication channel. Two types of FESs have been defined for the satellite network system; Gateway FESs and Base FESs. Gateway FESs provide MTS, MRS, MTCRS and NR services. Base FESs are for like services and/or value added services.

MET. The MET provides the mobile user access to the communications channels and services provided by the satellite network system. A range of terminal types has been defined for the satellite network system.

RMS. The RMS monitors L-band RF spectrum and transmission performance in specific L-band beams. An RMS is nominally located in each L-band beam. Each RMS interfaces with the NOC via either a satellite or terrestrial link.

STS. The STS provides an L-band network access capability to support FES commissioning tests and network service diagnostic tests. The STS is collocated with, and interfaced to, the NOC.

Communications channels transport voice, data and facsimile transmissions between METs and FESs via the satellite. Connectivity for MET-to-MET calls is accomplished by double hopping the communications channels via equipped FESs. Signaling channels are used to set up and tear down communications circuits, to monitor and control FES and MET operation, and to transport other necessary information between network elements for the operation of satellite network. The system provides Out-of-Band and Interstation signaling channels for establishing calls and transferring information. In-Band signaling is provided on established communications channels for supervisory and feature activation purposes. A detailed description of the satellite network signaling system architecture is provided in L. White, et al., "North American Mobile Satellite System Signaling Architecture," AIAA 14th International Communications Satellite Conference, Washington, D.C. (March 1992), incorporated herein by reference.

The satellite network Internetwork provides interconnection among the major satellite network ground system elements such as the NOCs, NCCs, and Data Hubs, as well as external entities. Various leased and dial-up lines are used for specific applications within the satellite network system such as backup interstation links between the NCC and FESs and interconnection of RMSs with the NOC.

The primary function of the NOC is to manage and control the resources of the satellite network system. FIG. 5 is a basic block diagram of the NOC and its interface. The NOC computer is shown with network connections, peripheral disks, fault tolerant features, and expansion capabilities to accommodate future growth. The NOC software is represented as two major layers, a functional layer and a support layer. The functional layer represents the application specific portion of the NOC software. The support layer represents software subsystems which provide a general class of services and are used by the subsystems in the functional layer.

The application specific functions performed by the NOC are organized according to five categories: fault management, accounting management, configuration management, performance management, and security management. The general NCC Terminal Equipment (NCCTE) configuration showing constituent equipment includes: processing equipment, communications equipment, mass storage equipment, man-machine interface equipment, and optional secure MET Access Security Key (ASK) storage equipment. The Processing Equipment consists of one or more digital processors that provide overall NCC control, NCS call processing, network access processing and internetwork communications processing.

The Communications Equipment consists of satellite signaling and communications channel units and FES terrestrial communication link interface units. The Mass Storage Equipment provides NCC network configuration database storage, call record spool buffering an executable program storage. The Man-Machine Interface Equipment provides operator command, display and hard copy facilities, and operator access to the computer operating systems. The MET ASK storage Equipment provides a physically secure facility for protecting and distributing MET Access Security Keys.

The NCCTE comprises three functional subsystems: NCCTE Common Equipment Subsystem, Group Controller Subsystem, and Network Access Subsystem. The NCCTE Common Equipment subsystem comprises an NCC Controller, NCCTE mass storage facilities, and the NCCTE man-machine interface. The NCC Controller consists of processing and database resources which perform functions which are common to multiple Group Controllers. These functions include satellite network Internetwork communications, central control and monitoring of the NCCTE and NCCRE, storage of the network configuration, buffering of FES and Group Controller call accounting data, transfer of transaction information to the Off-line NCC and control and monitoring of FESs.

The Mass Storage element provides NCC network configuration database storage, call accounting data spool buffering, and NCCTE executable program storage. The Man-machine Interface provides Operator command and display facilities for control and monitoring of NCC operation and includes hard copy facilities for logging events and alarms. A Group Controller (GC) is the physical NCC entity consisting of hardware and software processing resources that provides real time control according to the CG database received from the NOC.

The Group Controller Subsystem may incorporate one to four Group Controllers. Each Group Controller maintains state machines for every call in progress within the Control Group. It allocates and de-allocates circuits for FES-MET calls within each beam of the system, manages virtual network call processing, MET authentication, and provides certain elements of call accounting. When required, it provides satellite bandwidth resources to the NOC for AMS(R)S resource provisioning. The Group Controller monitors the performance of call processing and satellite circuit pool utilization. It also performs MET management, commissioning and periodic performance verification testing.

The Network Access Subsystem consists of satellite interface channel equipment for Out-of-Band signaling and Interstation Signaling which are used to respond to MET and FES requests for communications services. The Network Access Processor also includes MET communications interfaces that are used to perform MET commission testing. In addition, the subsystem includes terrestrial data link equipment for selected FES Interstation Signaling.

The principal function of the FES is to provide the required circuit switched connections between the satellite radio channels, which provide communications links to the mobile earth terminals, and either the PSTN or PN. FESs will be configured as Gateway Stations (GS). to provide MTS and MTCRS services or Base Stations to provide MRS and Net Radio services (described in detail below). Gateway and Base functions can be combined in a single station.

The FES operates under the real time control of the Network Communications Controller (NCC) to implement the call set-up and take-down procedures of the communications channels to and from the METs. Control of the FES by the NCC is provided via the interstation signaling channels. An FES will support multiple Control Groups and Virtual Networks. The FES is partitioned into two major functional blocks, the FES RF Equipment (FES-RE) and the FES Terminal Equipment (FES-TE). The principal function of the FES-RE is to provide the radio transmission functions for the FES. In the transmit direction it combines all signals from the communications and interstation signaling channel unit outputs from the FES-TE, and amplifies them and up-convert these to Ku-Band for transmission to the satellite via the antenna. In the receive direction, signals received from the satellite are down-converted from Ku-Band, amplified and distributed to the channel units within the FES-TE. Additional functions include satellite induced Doppler correction, satellite tracking and uplink power control to combat rain fades.

The principal function of the FES-TE is to perform the basic call processing functions for the FES and to connect the METs to the appropriate PSTN or PN port. Under control of the NCC, the FES assigns communications channel units to handle calls initiated by MET or PSTN subscribers. The FES-TE also performs alarm reporting, call detail record recording, and provision of operator interfaces.

For operational convenience, an FES may in some cases be collocated with the NCC. In this event, the NCC RF Equipment will be shared by the two system elements and the interstation signaling may be via a LAN. Connection to and from the PSTN is via standard North American interconnect types as negotiated with the organization providing PSTN interconnection. This will typically be a primary rate digital interconnect. Connection to and from private networks is via standard North American interconnect types as negotiated with the organization requesting satellite network service. This will typically be a primary rate digital interconnect for larger FESs or an analog interconnect for FESs equipped with only a limited number of channels may be employed.

We have discovered that there is a general need for an integrated mobile telephone that can be used to transmit to, and receive from, to communicate in a Closed User Group (CUG) arrangement that allows each member of the group to hear what any other user is saying. Each member of the group can also talk when needed. The system behaves like a radio multi-party line where several parties communicate over the same communication channel. Public services and law enforcement agencies are typical users of this service, which is normally provided by either traditional terrestrial radio networks or by the more recent trunked radio systems. These trunked systems, generally in the 800-900 MHz band, provide groups of end users with virtual private systems by assigning frequencies to CUGs on a demand basis. In this connection, however, we have discovered that an integrated mobile communication device is needed that provides this ability to communicate in a CUG of a satellite network. Further, we have discovered that if this type of satellite trunking utilizes a shared satellite demand period circuit per CUG rather than one circuit per mobile user, the cost per minute of a group conversation would be much less expensive to the owner of the group.

We have further discovered that there is the need to provide the capability for the Closed User Group arrangement to be used alternately with a private point-to-point voice communication between two parties.

We have also discovered that for Closed User Group communications, additional security procedures are required to ensure that unauthorized parties are unable to enter the group. In this connection, we have discovered that an efficient method for permitting parties access to the Closed User Group without being to cumbersome is required.

We have also discovered that the call set-up time for one shared circuit per CUG compared to a mobile radio service multi-user conference set-up time is likely to be more acceptable to a group end user/operator, who normally expects to be able to talk as soon as the handset/microphone is taken off-hook. Further, we have discovered the need for a nationwide and regional point-to-multipoint mobile communication service that is not limited in coverage.

We have also discovered that there is a need to provide a procedure for priority service for the Closed User Group arrangement under a default mode. That is, we have discovered the need to permit a MET user while communicating in a first closed user group to have the capability to efficiently transmit a priority message to a predetermined closed user group.

It is a feature and advantage of the present invention to provide an integrated mobile telephone that can be used to transmit and receive in a Closed User Group (CUG) arrangement that allows each member of the group to hear what any other user is saying.

It is another feature and advantage of the present invention to permit each member of the group to talk when needed, and to provide a system that behaves like a radio multi-party line.

It is a further feature and advantage of the present invention to provide an integrated mobile communication device that can communicate in a CUG of a satellite network.

It is a further feature and advantage of the present invention to provide additional security procedures are required to ensure that unauthorized parties are unable to enter the group for the Closed User Group.

It is another feature and advantage of the present invention to provide an inexpensive satellite trunking service to the owner of the group.

It is another feature and advantage of the present invention to minimize the call set-up time for one shared circuit per CUG.

It is another feature and advantage of the present invention to provide a procedure for priority service for the Closed User Group arrangement under a default mode.

It is another feature and advantage to provide a MET user, while communicating in a first closed user group, to have the capability to efficiently transmit a priority message to a predetermined closed user group.

It is another feature and advantage of the present invention to generally effectively and efficiently effectuate transmissions between mobile communication devices and the satellite network in a closed user group environment by utilizing an efficient communication protocol.

It is another feature and advantage of the invention to provide the capability for the Closed User Group arrangement to be used alternately with a private point-to-point voice communication between two parties.

It is another feature and advantage of the invention to provide a nationwide and regional point-to-multipoint mobile communication service that is not limited in coverage.

The present invention is based, in part, on the desirability of providing point-to-multipoint circuit switched connections between mobile terminal subscriber stations and a central base station. Mobile users are able to listen to two-way conversations and to transmit using a push-to-talk mode of operation.

To achieve these and other features and advantages of the present invention, a mobile communication system is provided in a mobile satellite system. The mobile satellite system includes a satellite communication switching office having a satellite antenna for receiving/transmitting a satellite message via a satellite from/to a vehicle using a mobile communication system, a satellite interface system, a central controller receiving/transmitting the satellite message from/to the satellite communication switching office issued from the vehicle via the satellite and the satellite interface system. The mobile communication system includes a user interface system providing a user interface through which a user has access to services supported by the mobile satellite system, and an antenna system providing an interface between the mobile communication system and the mobile satellite system via the satellite interface system, and receiving a first satellite message from the satellite and transmitting a second satellite message to the satellite. The antenna system includes an antenna including one of a directional and an omnidirectional configuration, a diplexer, an amplifier, a low noise amplifier, a beam steering unit when the antenna is of the directional configuration, and at least one of a compass and sensor to determine vehicle orientation. The mobile communication system also includes a transceiver system, operatively connected to the antenna system, including a receiver and a transmitter. The transmitter converts the second satellite message including at least one of voice, data, fax and signaling signals into a modulated signal, and transmits the modulated signal to the antenna system. The transmitter includes an amplifier, a first converter and associated first frequency synthesizer, a modulator, an encoder, multiplexer, scrambler and frame formatter for at least one of voice, fax, and data. The receiver accepts the first satellite message from the antenna system and converts the first satellite message into at least one of voice, data, fax and signaling signals, at least one of the voice, data and fax signals routed to the user interface system. The receiver includes a second converter with an associated second frequency synthesizer, a demodulator, a decoder, demultiplexer, descrambler and frame unformatter for at least one of voice, fax, and data. The mobile communication system also includes a logic and signaling system, operatively connected to the transceiver, controlling initialization of the mobile communication system, obtaining an assigned outbound signaling channel from which updated system information and commands and messages are received. The logic and signaling system configures the transceiver for reception and transmission of at least one of voice, data, fax and signaling messages, and controls protocols between the mobile communication system and the mobile satellite system, and validating a received signalling messages and generating codes for a signaling message to be transmitted.

In one embodiment of the invention, a system for providing satellite communication between multiple users in a closed user group arrangement includes first and second mobile earth terminals (METs) responsively connected to and registering with the mobile satellite system. The first MET selects a closed user group network identifier (NET ID) representing a NET group including the first and second METs to establish voice communication therewith and transmits the NET ID to a central controller. The central controller receives the NET ID from the first MET, validates the first MET for communication, validates the NET ID, allocates a frequency for the NET group, and broadcasts the message to the NET group including the second MET informing the NET group of the allocated frequency and the voice communication associated therewith. The second MET tunes to the frequency in response to the message broadcast by the central controller, and the central controller assigns the first MET as current speaker for the NET group.

In another embodiment of the invention, a method of providing satellite communication between multiple users in a closed user group arrangement includes the steps of first and second mobile earth terminals (METs) registering with the mobile satellite system, the first MET selecting a closed user group network identifier (NET ID) representing a NET group including the first and second METs to establish voice communication therewith. The method also includes the steps of the first MET transmitting the NET ID to the central controller, the central controller receiving the NET ID, validating the first MET for communication, validating the NET ID, allocating a frequency for the NET group, and broadcasting the message to the NET group including the second MET informing the NET group of the allocated frequency and the voice communication associated therewith. The method also includes the steps of the second MET tuning to the frequency in response to the message broadcast by the central controller, and assigning by the central controller the first MET as current speaker for the NET group.

In another embodiment of the invention, the method also includes the step of monitoring by the first and second METs whether at least one of a dispatcher message, a priority message and a release of speaker message has been issued, and if so, interrupting the current speaker with the at least one of the dispatcher message, the priority message and a new speaker. The method also includes the steps of monitoring by the central controller whether the current speaker is active, and if not, removing the current speaker and setting the current speaker to vacant, notifying by the central controller the first and second METs that the current speaker is vacant, and initiating by one of the first and second METs a request to be the new speaker. The method further includes the steps of receiving by the central controller the request from a first of the one of the first and second METs to be the new speaker, and assigning the first of the one of the first and second METs as the new speaker, and releasing the closed user group communication when no request from the one of the first and second METs is made to be the new speaker for a predetermined period of time.

In another embodiment of the invention, the method also includes the steps of a third MET included in the NET group registering with the mobile satellite system, and the central controller broadcasting the message to the NET group including the third MET informing the NET group of the allocated frequency and the voice communication associated therewith. The method also includes the steps of the third MET tuning to the frequency in response to the message broadcast by the central controller by generating a scrambling vector for access thereto. The third MET gains access to the frequency and the voice communication of the NET group using the scrambling vector.

According to the invention, the central controller advantageously controls the closed user group satellite communication including net radio parameters used by the first and second METs. The central controller also selectively downloads the NET IDs to the first and second METs according to predetermined user criteria.

The central controller advantageously collects billing information regarding the closed user group satellite communication and transmits the billing information to the mobile satellite system. The mobile satellite system optionally charges a service fee to a customer that has requested the closed user group arrangement instead of each of the individual users in the NET group thereby consolidating the billing transactions and permitting a single customer to monitor communication charges.

In another embodiment of the invention, the method includes the steps of a non-MET accessing the mobile satellite system via either a public switched telephone network or a cellular network to initiate a closed user group communication with the NET group including at least one of the first and second METs, the central controller broadcasting the message to the NET group informing the NET group of the allocated frequency and the voice communication associated therewith, and the at least one of the first and second METs tuning to the frequency in response to the message broadcast by the central controller to communicate with the non-MET in the closed user group arrangement.

In another embodiment of the invention, the method includes the steps of the first MET selecting the closed user group network identifier (NET ID) representing a NET group including the first MET and a non-MET serviced by one of a public switched telephone network and a cellular network to establish voice communication therewith, and the first MET transmitting the NET ID to the central controller. Additionally, the method includes the central controller receiving the NET ID, determining that the NET group includes the non-MET, and broadcasting a non-MET message to either the public switched telephone network or the cellular network including the voice communication associated therewith, and either the public switched telephone network or the cellular network receiving the non-MET message from the central controller and transmitting the non-MET message to the non-MET to establish the closed user group arrangement between the MET and the non-MET.

The first MET beneficially includes a push to talk (PTT) device for generating the release of speaker message. The first MET activates the PTT device generating a PTT signal only when the PTT device is activated after the current speaker is vacant, relieving congestion on the satellite by selectively transmitting the PTT signal.

The central controller advantageously selectively downloads monitor codes to the first and second METs according to predetermined user criteria. The monitor code functions to lock the first and second METs to the NET group preventing the NET group from being released when no request has been made by the first or second METs to be the current speaker after the predetermined period of time.

In another embodiment of the invention, a priority default operation is provided. The first MET and the central controller implement the following operations:

(1) assigning, by the first MET, a default priority NET group for receiving a priority message when a priority button of the first MET is activated;

(2) activating, by the first MET, the priority button of the first MET to initiate the priority message to be transmitted to the default priority NET group even when the first MET is active in the NET group, wherein the default priority NET group is potentially different than the NET group;

(3) tuning, by the first MET, to a GC-S channel and transmitting a Net Radio Access Request Signalling Unit (NRACRSU) with a priority code appended on a corresponding receive channel indicating the default priority NET group;

(4) receiving, by the central controller, the NRACRSU and performing a MET originated NET Radio call setup procedure;

(5) rebroadcasting by the central controller the NET Radio Channel Assignment (NRCHASU) on the GC-S channel identified in the Net ID or that are active;

(6) transmitting by the central controller the NRCHASU a predetermined number of times in a predetermined number of consecutive superframes for a NET Radio channel assignment;

(7) setting by the central controller, the priority code and including a call identifier in the GC-I channel assignment message; and

(8) tuning, by the first MET, to the NET Radio channel assignment and proceeding with the voice communication.

In another embodiment of the invention, security measures are provided to prevent unauthorized METs from entering or accessing a closed user group communication. According to this aspect of the invention, a MET storing a first security key generates a scrambling vector for access to the voice communication. The scrambling vector is generated in accordance with the following operations:

(1) generating a second security key having first and second components using a first process having first and second input signals, the first input signal comprising the first security key and the second input signal comprising at least one of a transmit frequency and a receive frequency; and

(2) generating the scrambling vector responsive to the second security key.

The second MET tunes to the allocated frequency for the NET group using the scrambling vector to gain access thereto.

In another embodiment of the invention, the system further provides dual standby operation permitting voice communication alternately between a closed user group arrangement (NET radio) and a mobile telephone service (MTS). At least one of the first and second METs implement the function of responding either to a MTS page request indicating the mobile telephone service is being requested or to a NET radio channel assignment request as transmitted on a GC-S channel. When one of the first or second METs responds to a service request of either the closed user group arrangement or the mobile telephone service, the first or second MET is not required to monitor the GC-S channel for service requests for the other service.

These together with other objects and advantages which will be subsequently apparent, reside in the details of construction and operation as more fully herein described and claimed, with reference being had to the accompanying drawings forming a part hereof wherein like numerals refer to like elements throughout.

FIG. 1 is a diagram illustrating an overview of the satellite network system;

FIG. 2 is a diagram illustrating key performance parameters of the satellite used in the satellite network system;

FIG. 3 is a diagram of the satellite network system illustrating components and respective interfaces;

FIG. 4 is a diagram of a satellite network system illustrating a number of system elements and their interconnecting communications links;

FIG. 5 is a basic block diagram of the NOC and its interfaces;

FIG. 6 is a basic block diagram of the physical architecture of the mobile earth terminal;

FIG. 7 is a basic block diagram of the functions of the mobile earth terminal;

FIG. 8 illustrates the basic concept and elements involved in establishment of communications and control in the Net Radio system;

FIG. 9 is a diagram of an example of a Net Radio service subscribing organization with several communication nets;

FIGS. 10A-10C are flowcharts of the overall process conducted by the various components in establishment of communications and control in the Net Radio system;

FIG. 11 illustrates the service categories for Net Radio;

FIG. 12 illustrates the additional GC-S messages in each group;

FIG. 13 is an illustration of the format of the NID.sub.-- SU;

FIG. 14 is an illustration of the content of the NID-SU;

FIG. 15 is an illustration of the format of the NA.sub.-- SU;

FIG. 16 is an illustration of the content of the NA.sub.-- SU;

FIG. 17 is an illustration of the format of the NRCHA.sub.-- SU;

FIG. 18 is an illustration of the content of the NRCHA-SU;

FIG. 19 is an illustration of the MET-ST messages that are of the Network Management Category;

FIG. 20 is an illustration of the format of the MA.sub.-- SU;

FIG. 21 is an illustration of the content of the MMA-SU;

FIG. 22 is an illustration of the format of the NRACR.sub.-- SU;

FIG. 23 is an illustration of the content of the NRACR-SU;

FIG. 24 is an illustration identifying the messages in each call control group;

FIG. 25 is an illustration of the content of the PTT-SU;

FIG. 26 is an illustration identifying MET timing requirements;

FIG. 27 is an illustration identifying MET call monitor codes;

FIG. 28 is an illustration of a MET originated net radio call message flow;

FIG. 29 is an illustration of a MET originated Net Radio call setup event tree;

FIG. 30 is an illustration of a symbol key for use in the various figures including the event tree figures;

FIG. 31 is an illustration of a MET call monitoring event tree;

FIG. 32 is an illustration of a MET call supervision event tree;

FIG. 33 is an illustration of a MET PTT frame structure;

FIGS. 34(a)-(c) are illustrations of a Net Radio call release message flow and frame structure;

FIG. 35 is an illustration of a perceived hangtimer for MET users;

FIG. 36 is an illustration of a MET originated private mode call setup message flow;

FIG. 37 is an illustration of a MET Priority 1 event tree;

FIG. 38 is a diagram of the Net ID ASK security key generation process;

FIG. 39 is a diagram of the Authentication Security Key generation process;

FIG. 40 is a diagram of the Access Security Check Field and Secondary Security Check Field generation process;

FIG. 41A is a flow chart of the keying process;

FIG. 41B is an illustration of the keying process in the satellite communication system;

FIG. 41C is a signal/data diagram of the keying process;

FIG. 42 is a diagram of a bulletin board in the satellite communication system;

FIG. 43 is a diagram of the scrambling vector generation process for the NET Radio service;

FIGS. 44A and 44B are diagrams of the authentication process using the authentication security key generated by the process described in FIGS. 41A-41C;

FIG. 45 is a diagram of the form of the "plain text input" used in the PIN-inclusive ASCF generation process;

FIG. 46 is a glossary of additional commonly used acronyms.

The present invention provides point-to-multipoint circuit switched connections between mobile terminal subscriber stations and a central base station. Mobile users are able to listen to two-way conversations and to transmit using a push-to-talk mode of operation.

The MET includes all of the communication and control functions necessary to support communications from a vehicle or fixed remote site using the resources of the satellite network system. FIGS. 6 and 7 are basic block diagrams of the physical architecture and functions of the mobile earth terminal. The basic functional diagram of FIG. 7 is implemented by baseband processing and RF electronics of FIG. 6. A standard voice coder/decoder receives coded messages from the baseband processing and RF electronic system and decodes the message received from the satellite antenna unit for delivery to the interface unit that includes standard user interfaces. Baseband processing and RF electronics receive satellite communications responsive with low noise amplifier (LNA) and output signals for transmission using the diplexer of the antenna unit. Baseband processing and RF electronics also outputs signals for use with beam steering antennas as will be discussed blow. Advantageously, the mobile earth terminal is functional with antennas that are either steerable or nonsteerable.

The functional subsystems comprising the MET are shown in FIG. 7 and include the user interface, transceiver, antenna, logic and signaling, power supply subsystems, and Position Determination subsystem. The baseline MET will have a low gain directional antenna in the antenna subsystem. The satellite network system supports communications with METs using omnidirectional and higher gain directional antennas.

The user interface subsystem provides the user interfaces through which the user has access to the services supported by the satellite network system. Depending on the service(s) the MET will be equipped with one or more of the devices or ports. The transceiver subsystem consists of a receiver and a transmitter. The transmitter accepts voice, data, fax and signaling signals and converts them to a modulated RF signal. The transmit RF signal is routed to the antenna subsystem. The transmitter typically consists of the high power amplifier (HPA), the upconverter with its associated frequency synthesizer, the modulators and the modules for voice, Fax, or data encoding, multiplexing, scrambling, FEC encoding, interleaving and frame formatting.

The receiver accepts modulated RF signals from the antenna subsystem and converts them into voice, data, fax or signaling signals as appropriate. The voice, data and fax signals are routed to the user interface subsystem. The receiver typically consists of the downconverter with its associated frequency synthesizer, the demodulator, and the modules for frame de-formatting, de-interleaving, FEC decoding, descrambling, demultiplexing and voice, Fax, or data decoding. The transceiver communicates over one channel in each direction at any one time. Thus, the transceiver subsystem will typically consist of only one receiver and one transmitter. However, the MET may also incorporate a pilot receiver for antennas and frequency tracking purposes, or a complete receiver dedicated to the continuous reception of the signaling channel from the Group Controller.

The antenna subsystem provides the MET interface to the satellite network and is responsible for receiving the RF signal from the satellite and transmitting the RF signal generated by the MET towards the satellite. The subsystem typically includes an antenna which may be either directional or omnidirectional, a diplexer, a low noise amplifier (LNA), an optional beam steering unit (BSU) if a directional antenna is used, a device such as a compass or an inertial sensor for the determination of the orientation of the vehicle, and an antenna for the position determination receiver.

The logic and signaling subsystem acts as the central controller for the MET. Its basic functions are to initialize the MET by performing a self test at power up and control, based on a resident system table, the acquisition of one of the METs assigned outbound signaling channels from which updated system information and commands and messages from the GC are derived. The logic and signaling subsystem sets up and configures the transceiver for the reception and transmission of voice, data, fax or signaling messages as appropriate. The logic and signaling subsystem also handles the protocols between the MET and the FES and between the MET the GC via signaling messages, and checks the validity of the received signaling messages (Cyclic Redundance Check (CRC)) and generates the CRC codes for the signaling message transmitted by the MET.

The logic and signaling subsystem also interprets the commands received from the local user via the user interface subsystem (e.g. on/off hook, dialled numbers, etc.) and take the appropriate actions needed, and generates, or commands the generation, of control signals, messages and indications to the user through the user interface subsystem. The logic signaling system also controls the beam steering unit (if any) in the antenna subsystem, and monitors and tests all the other subsystems. In case of fault detection, it informs the user about the failure and take the appropriate measures needed to prevent harmful interference to the satellite network or other systems.

The power supply subsystem provides power to all other subsystems. The external voltage source to which this subsystem interfaces depends on the type of vehicle on which the MET is mounted (e.g. 12/24 Volts DC for land vehicles).

A standard receiver such as a GPS or a Loran-C receiver is also provided for the determination of the position of the vehicle. This information is used by the logic and signaling subsystem for beam steering (if used) or for applications such as position reporting. The position determination system is implemented externally to the MET and interfaced through a dedicated data port in the user interface subsystem.

The function of the Remote Monitor System is to continuously monitor the activity on each GC-S channel and to monitor the activity within the downlink L-band spectrum in the beam in which it is located. An RMS will be located in every beam carrying satellite network traffic. An RMS may be a stand alone station or collocated with the NCC or an FES. The RMS is controlled by the NOC and communicates via leased lines or the interstation signaling channels if collocated with an FES. The RMS detects anomalous conditions such as loss of signal, loss of frame sync, excessive BER, etc. on the GC-S channels and generates alarm reports which are transmitted to the NOC via the leased line interface. In addition, it monitors BER on any channel and power and frequency in any band as instructed by the NOC.

The primary functions of the System Test Stations (STS) is to provide commission testing capability for every channel unit in a FES and to provide readiness testing for the Off-Line NCC. The STS is collocated with and controlled by the NOC and will comprise one or more specifically instrumented METs. The STS provides a PSTN dial-up port for making terrestrial connections to FESs to perform MET to terrestrial end-to-end testing. The STS also provides a LAN interconnection to the NOC to provide access to operator consoles and peripheral equipment.

Advantageously, the MET combines three different features for the delivery and transmission of voice and data. These three features include: the ability to initiate and transmit a data call, the ability to initiate and transmit a facsimile digital call, and the ability to roam between satellite and terrestrial based wireless communication systems. The following documents, representing applicable transmission protocols, are hereby incorporated by reference: EIA/IS-41B Cellular Radio Telecommunications Inter-System Operations; EIA/TIA-553-1989 "Cellular System Mobile Station--Land Station Compatibility Standard"; EIA/TIA-557; EIA/IS-54B. A more detailed description of the MET is also provided in U.S. provisional patent application serial number 60/002,374 filed on Aug. 15, 1995 to Ward et al., entitled "Improved Mobile Earth Terminal" incorporated herein by reference.

Some MSS system users have voice communication requirements that are not met by MTS and Mobile Radio Service (MRS). They need to communicate in a Closed User Group (CUG) arrangement that allows each member of the group to hear what any other user is saying. Each member of the group can also talk when needed. The system behaves like a radio multi-party line. Public services and law enforcement agencies are typical users of this service, which is normally provided by either traditional terrestrial radio networks or by the more recent trunked radio systems. These trunked systems, generally in the 800-900 MHz band, provide groups of end users with virtual private systems by assigning frequencies to CUGs on a demand basis. The Net Radio service is meant to be the satellite equivalent of terrestrial trunked systems ("trunking" for short), and could be pictured as a "Satellite Trunked Radio Service", or "Satellite Trunking".

The Net Radio service provides the capability described in the previous paragraph in a cost effective manner:

as one shared satellite demand period circuit per CUG is utilized rather than one circuit per mobile user, the cost per minute of a group conversation would be much less expensive to the owner of the group, and

as the call set-up time for one shared circuit per CUG compared to an MRS multi-user conference set-up time is likely to be more acceptable to a group end user/operator, who normally expects to be able to talk as soon as the handset/microphone is taken off-hook.

An overview of the MSS system with Net Radio service is illustrated in FIG. 8. FIG. 8 illustrates the basic concept and elements involved in establishment of communications and control in the Net Radio system. METs access the system via one or more L-band beams. Each beam contains one or more signaling channels for network control and call establishment and a number of communications channels for provision of Net Radio services to METs.

The L-band frequencies are translated to Ku-band frequencies by the satellite 12. The Network Control Center 14 is responsible for the real time allocation of channels to support Net Radio calls. The base Feederlink Earth Station 16 is responsible for re-transmission on the outbound channel of the MET transmissions received on the inbound channel, control of the Net Radio call, and interfacing the Net Radio call to terrestrial private networks.

Net Radio service is available to CUGs on subscription to MSS. A subscribing organization may comprise a number of METs grouped by their communication needs. A virtual private communication net is established for each of these groups or subgroups.

The base FES 16 can interconnect the Net Radio call to terrestrial private networks so that a dispatcher located within the private network can participate in the conversation. A Dispatch facility may be directly connected to the base FES 16, or may use leased PSTN or dial-up access, or may use a Mobile Radio Service (MRSA) circuit. An example of a Net Radio service subscribing organization with several communication nets is depicted in FIG. 9.

The Net Radio MET operates in CUG and receives voice transmissions from all other MET users in the same CUG, and the base FES. The MET supports Net Radio service on a single demand period circuit per beam, which is shared by the entire CUG. The MET requiring communications will be given the Net ID for the net and since different nets may be necessary for different purposes, the MET may be given a number of different NET IDs. NET IDs may represent organizational groups such as fleets or sub-fleets. NET IDs may represent functional groups such as a command unit which draws on mobile users from more than one fleet or sub-fleet. NET IDs may represent geographic configurations such as an east or west area, or both.

A mobile user requests a channel on a Push-To-Talk (PTT) basis. The MET receives an assignment of demand period satellite resources consisting of an outbound channel frequency and an inbound channel frequency relevant to the particular NET ID (per defined CUG beam). The mobile user is alerted by a tone when the channel is available and the base FES manages the contention on the communications channel. Since the base FES retransmits the signal received from the mobile, the MET operates in a half duplex PTT mode, turning off the speaker while the microphone is engaged. When the user releases the PTT, the MET ceases transmission. On receipt of a release message from the base FES, the MET retunes to the signaling channel.

FIGS. 10A-10C are flowcharts of the overall process conducted by the various components in establishment of communications and control in the Net Radio system. In FIGS. 10A-10C, a mobile earth terminal registers in step S2 and the user of the mobile earth terminal selects a particular net to establish voice communication therewith in step S4. The user then activates the push-to-talk (PTT) button of the MET in step S5.

In step S6, the MET sends the net number to the communication ground segment. The communications ground segment receives the net number, checks the message for transmission errors, validates the specific MET user and also validates the requested net group in step S8. The communications ground segment allocates a specific frequency for the net group and broadcasts the message to the net group informing the net group of the allocated frequency in step S10.

The group controller in the communications ground segment will also send the net frequency to the feeder link earth station in step S12. In step S14, the METs that are idle, powered and logically consistent with respect to monitor codes and lock discussed below, will tune to the net frequency indicated by the communication ground segment. Channel assignment is thereupon completed and no further validation for the net group is performed in step S16. A scrambling vector is next used to permit additional METs to join the selected net group in step S18. All METs are assumed to have joined the net group in step S20. CGS will continue to broadcast NET group activation information at predetermined time intervals while the NET group is active.

The MET user which initiates the Net Radio call is considered to be the current speaker in step S22 permitting the initiator to communicate with the various MET users that have joined the net group. The MET monitors whether a dispatcher message has been received in step S24, and if so the current speaker is set to the dispatcher, and the communication is broadcast to all METs in the NET group in step S26. The MET also monitors receipt of the priority message in step S28, and if a priority message is received, sets the current speaker to the identifier of the priority MET, and the communication is broadcast to all METs in the NET group in step S29.

If no dispatcher message or priority message is received, the MET also monitors whether the current speaker is active in step S30. If speaker is active for the requisite period of time, the MET also determines whether the push-to-talk button has been released in step S32. If either the speaker is inactive for greater than a predetermined threshold period of time as determined in S30 or the push-to-talk button has been released as determined in step S32, the current speaker is removed by the communications ground segment in step S34, and the current speaker is set to vacant in step S36. The communication ground segment will then notify the METs in the net group that the speaker is vacant in step S38.

The METs will then be permitted to initiate a request to be the next current speaker. Upon receipt of the first valid request from a MET to be the next speaker in step S40, the communications ground segment will assign the new speaker to that particular MET in step S42. If, however, no request from a MET is made to be the next speaker, the communications ground segment will determine whether or not the hang timer has expired in step S44. If the hang timer has expired, the communications ground segment will release the call to the METs of the net group in step S46. The feeder link earth station will also initiate a call release to the ground controller in step S48 and the ground controller will release the frequency channel which was being used for the net group in step S50.

The MET supports the service categories for Net Radio listed in FIG. 11. MSS will support addressing methods that permit private communications between a mobile end-user and groups or sub-groups of end users, or an individual, where the individual is part of the same group. NET IDs are utilized, where a NET ID can represent either a group, sub-group or individual. MSS supports addressing methods that permit a mobile end user to engage in a private conversation with another mobile where the called mobile is part of the same virtual network as the calling mobile.

It should be noted that even on private mobile to mobile calls the PTT has to be used, as the two mobile units share the same satellite circuit. This is the main difference between MRS and Net Radio for mobile to mobile calls. The MET monitors the NET Radio Channel Assignment SUs (NRCHA.sub.-- SU) s on the GC-S channel for those containing any of its stored NET IDs and, if not engaged in a Priority call or set-up procedure, responds to assignments in accordance with the current setting of the call monitoring.

The MET provides a User ID display for the purpose of displaying the NET ID the MET is currently tuned to, and the MET DN of the current speaker. The MET optionally displays an alpha-numeric display or user programmable label associated with a NET ID. When suitably equipped with a second receiver capable of continuously receiving the GC-S channel, the MET provides the user with notification of incoming calls, which the user may accept or reject.

This section provides the formats of several SUs used by the MET that are additional for Net Radio service. A separate section is generally provided for each channel type (GC-S, MET-SR, FES-C, MET-C).

The SUs transmitted on the GC-S signaling channel that are additional for Net Radio shall conform to the content and format specified in this section. The messages are required for Network Management and Call Control. FIG. 12 identifies the additional GC-S messages in each group.

1. The NID.sub.-- SU is transmitted by the NCC to a MET on the GC-S channel. The NID.sub.-- SU is used to download a NET ID assignment to a MET subscribing to Net Radio Service.

2. The NID.sub.-- SU has the format illustrated in FIG. 13. The content of the NID-SU conforms to FIG. 14.

NET ID Attribute (NA)

The NA message is used to allocate and de-allocate NET IDs assigned to a MET, to change a METs Directory Number (DN), or to Change the user defined characteristics of a NET ID assigned to a MET. The NA.sub.-- SU has the format illustrated in FIG. 15. The content of the NA-SU conforms to FIG. 16.

Net Radio Channel Assignment (NRCHA)

The NRCHA message is used by the GC to broadcast the channel assignments to the METs for a Net Radio call. The SU is broadcast on all GC-S channels defined for the NET ID. The NRCHA.sub.-- SU has the format illustrated in FIG. 17. The content of the NRCHA.sub.-- SU conforms to FIG. 18. This message is rebroadcast on the GC-S channel every predetermined time interval (e.g., every 10 seconds) for the duration of activity of the NET communication.

The SUs transmitted on the MET-SR and MET-ST signaling channel that are additional for Net Radio conform to the content and format specified in this section. The MET-SR messages are of the Call Control category. The MET-ST messages are of the Network Management Category. FIG. 19 identifies the messages.

MET Management Acknowledge (MMA)

The MMA.sub.-- SU is used by METs to acknowledge NID and NA messages received from the GC. The MMA.sub.-- SU has the format illustrated in FIG. 20. The content of the MMA.sub.-- SU conforms to FIG. 21.

Net Radio Access Request (NRACR)

The NRACR.sub.-- SU shall be used by METs to initiate Net Radio calls. The SU message has the format illustrated in FIG. 22. The content of the NRACR.sub.-- SU conforms to FIG. 23.

The SUs transmitted on the FES-C signaling channel that are additional for Net Radio conform to the content and format specified in this section. The messages are of the Call Control category. FIG. 24 identifies the messages in each group.

Net Radio Call Release (NRCR)

The NRCR.sub.-- SU shall be used to broadcast the NET ID to the METs during a Net Radio call and to indicate to the METs that the channel assignment for the Net Radio call is about to be released. The NRCR.sub.-- SU has similar format and content as described above.

The SUs transmitted on the MET-C signaling channel that are additional for Net Radio conform to the content and format specified in this section. The messages are of the Call Control category.

Push-To-Talk (PTT)

The PTT.sub.-- SU is used to request access to the inbound channel for a Net Radio call. The PTT.sub.-- SU has the content conformed to FIG. 25. The Response SU shall be used by the MET to respond to FES-C Command SUs received on the FES-C channel. The Response SU shall have the same format and contents as specified for the FES-C Command SU. The Reserved field is reserved for future user defined requirements. The MET timing requirements for Net Radio service are illustrated in FIG. 26.

Push-to-Talk Operation

In the NET Radio service the operation of the PTT resembles terrestrial trunked radio systems. A PTT microphone/handset or the like is needed for Net Radio. Depressing the PTT switch when the current NET is unassigned shall result in the transmission of a NRACR.sub.-- SU with the intent of requesting the assignment of a channel to the selected NET ID, subject to the availability of resources. Depressing the PTT switch while the selected NET ID is active and the speaker ID is vacant shall result in the transmission of a PTT.sub.-- SU request on the communications channel followed by the transmission of voice frames in accordance with the standard MET call supervision procedures. If the MET has not selected a NET ID and the MET is not active in a NET Radio Call, then the MET ignores the PTT request.

Depressing of the PTT results in transmission of a PTT.sub.-- SU only if the PTT is pressed after the speaker ID is equal to the vacant code or the METs DN. This will relieve congestion on the MET-C channel by adding a natural delay. If the MET user depresses the PTT before the speaker ID is vacant or matches the METs DN, the MET ignores the request.

Priority 1 service is granted to a MET, not based on the PTT, but only by activation of the Priority 1 Button. Activation of the Priority 1 Button shall result in a Priority 1 call. The user is given immediate access to the channel and retains it until he releases his PTT, is preempted by another Priority request generated by another MET user, or is preempted by a dispatcher PTT. If he wishes to make another Priority 1 transmission it shall be necessary to repeat the procedure.

The re-transmitted signal appears to the MET user as a delayed echo where the delay time is the double satellite link transmission delay time. For this reason, the speaker is disabled while the user is talking. The MET operates in half duplex from the user's viewpoint, but operates in full duplex over the satellite channels.

MSS Network Management assigns each communication net a Net Radio Identification (NET ID) number when the subscribing organization defines the net. A MET is also assigned a number of NET IDs to use. The MET stores in non-volatile RAM a GSI code for Net Radio service. The MET uses this GSI in selecting a GC-S channel while providing Net Radio service. The MET also stores a directory number (DN) with a maximum of 4 digits. The MET DN is downloaded to the MET at the completion of the commissioning process. If the MET receives an NA.sub.-- SU with operator field equal to 3, the MET stores the specified DN as its new DN.

The MSS Network Management assigns a unique 16 bit access security code to each NET ID defined. The MET uses the NET access security code (NET ID ASK) to determine a standard scrambling vector used to initialize the channel unit scrambler for transmit and receive Net Radio calls. The MET determines the scrambling vector using as input:

the NET ID Access Security Key (ASK)

the transmit Frequency Assignment

the Receive Frequency Assignment.

A Net Radio subscriber can customize the organization of communications nets. User defined NET ID attributes, a NET ID Tag number, and a Monitor code, are associated with the NET ID for this purpose. The Tag number is used to designate a selector position, or memory location to the NET ID to. When the MET operator sets the selector switch to a position, the MET uses the NET ID with the Tag number that corresponds to the selector position. This permits a CUG to setup all METs with the same selection positions for emergency nets for example.

The monitor codes are identified in FIG. 27 and are used to control which channel assignments the MET responds to. During a lull in the conversation where the hangtimer has expired (described below), the MET receives a channel assignment to a NET ID other than the one that was just tuned to. If the MET tunes to the new net, the operator may miss the next conversation on the previous net. At the same time, the monitor code permits the organization to setup nets which can reach entire fleets, or emergency teams even though all member METs have not selected that NET ID. In this case a monitor code for a required response is associated with the NET ID.

A Net Management System (NMS) permits a Net Radio subscribing organization to customize their communication nets by assigning NET IDs to METs, changing NET ID assignments, or modifying the user defined attributes of a NET ID assigned to a MET. These changes are made by contacting or interfacing with customer billing support system/personnel. The NMS enters the changes in the NOC customer configuration database. The NOC disseminates this information to the NCC, which downloads the changes to the MET "over the air" from the GC-S channel.

The MET uses acknowledged MGSP message pairs for Net Radio MET management. Upon receipt of a NID SU addressed to it, the MET de-encrypts the NET ID NRASK using the METs ASK and RTIN, and stores that NET ID and the NRASK associated with the NET ID in non-volatile memory. The MET then sends the MMA SU to the GC. The MET stores multiple NET IDs, and an ASK is stored with each NET ID.

Upon receipt of the NET ID Attribute SU, the MET performs operations indicated in the SU. The MET sends the MMA SU to the GC. The MET examines the Tag number contained in the NET ID Attribute SU (NA.sub.-- SU) and, provided the Operator field equals a predetermined number, uses this number to determine the Tag position of the NET ID Selector switch to associate with that particular NET ID. For example, for a Tag number of zero the MET stores the NET ID in Tag location 00, which is reserved for Private Mode. If the Operator field in the NA.sub.-- SU equals a predetermined number, for example 1, the MET erases the specified NET ID from memory.

The MET supports the following responses to the Monitor codes contained in the NA.sub.-- SU. The MET provides a means for the user to select one of the NET IDs and "lock-on" to it. When so selected, the MET does not respond to the NET ID assignments with monitor code 00 or 01, but responds to assignments with 11 code.

The sequence of information exchanged between the MET, GC, and FES is for the purpose of demand period circuit assignment for Net Radio service, Private Mode service, Priority 1 service and Broadcast service calls. A call is described in five parts; channel assignment, call establishment, call monitoring, call supervision and call release. Channel assignment includes the network access procedures. Call establishment includes the procedures followed by the FES and the MET to initiate a Net Radio call. Call monitoring includes the procedures performed by the MET during a call. Call supervision includes procedures, performed by the FES, which provide contention resolution for MET access to the inbound channel. Call release includes those procedures used by the FES to terminate a call and release the demand period circuits.

METs place and accept voice calls to/from members of the closed user group and a private network connected at a base FES. The GC controls access to the satellite resources. The base FES provides the Net Radio function of re-transmitting the mobile transmissions so that all member METs participating in the call can hear both sides of the conversation. The FES provides access to the private network.

MET originated Net Radio calls are established using the sequence of messages shown in FIG. 28. The protocol employed is as specified in the event tree in FIG. 29. Upon receiving a NRACR-SU, the GC verifies, based on the requesting MET RTIN that:

the MET is an operational Net Radio user;

the MET is authorized to originate a Net Radio call using the NET ID included in the NRACR.sub.-- SU;

the required satellite capacity is available;

the call type in the NET ID data base file is for Net Radio service.

The GC verifies that the MET which requested the Net Radio call is in a beam included for the NET ID. If for any reason the call cannot be completed the GC sends a Call Failure SU using MGSP to the mobile terminal with the cause of failure indicated in the cause indication parameter.

Once the GC determines that the call can be completed it will select frequency assignments for a FES-C communication channel and a MET-C communication channel and format a NRCHA SU with the NET ID for the call, and the call type set to Net Radio service. The FES begins transmitting Net Radio SUs (NR.sub.-- SU) using the In-band signaling mode. The NET ID and requesting MET Directory Number are included in the NR.sub.-- SU. The FES starts the Lost Speaker timeout (Nominally, for example, 3.5 secs). The FES also connects the Net Radio call to a dispatcher, as appropriate.

Upon reception of the NRCHA.sub.-- SU on the GC-S channel, the MET stops timer T.sub.M 24 and checks the call type. For Net Radio service call types, the MET tests the NET ID to determine what action to take. If the NET ID received matches one of the NET IDs assigned to the MET and if one of the following conditions is true, the MET accepts the Net Radio channel assignment and tunes to the assigned frequencies. If the NET ID does not match any NET ID assigned to the MET, or if none of the following case is true, then the MET ignores the NRCHA.sub.-- SU and remains tuned to the GC-S channel.

Case 1: The Monitor code for the NET ID indicates a mandatory response.

Case 2: The Monitor code for the NET ID indicates a conditional response and the condition criteria permit the MET to respond to the assignment.

If the MET accepts the Net Radio channel assignment, then it alerts the user to the Net Radio call with appropriate audio and/or visual displays. The MET then starts timer T.sub.M 1. (Nominally, for example, 10 seconds). If timer T.sub.M 24 expires, or a call failure is received, the MET indicates call failure to the user. Upon acquisition of the FES-C channel, the MET stops timer T.sub.M 1 and decodes the NR.sub.-- SU using the scrambling vector determined from the Access Security Key. If the MET has a Net Radio call request outstanding, it verifies the NET ID and confirms that its user's Directory Number matches the Speaker ID. If there is no outstanding request, the MET only verifies the NET ID.

The MET tests the speaker ID and if it matches its DN, it generates an audio and/or visual alert to the user and enable transmission. If T.sub.M 1 expires or the NET ID received on the communications channel does not match the assigned NET ID, the MET indicates call failure to the user and retunes to the GC-S channel.

MET Call Monitoring Procedure

MET Call Monitoring defines the procedures followed by a MET while assigned to a Net radio call. The MET monitors the FES-C channel and operates timers on loss of the carrier. The procedures determine when to permit PTT requests, disable transmission, or re-tune to the GC-S channel. After accepting a NRCHA.sub.-- SU and tuning to the assigned frequencies for a net radio call, a MET follows the call monitoring procedures specified herein and as shown in FIG. 31.

Upon accepting the NRCHA.sub.-- SU the MET starts timers T.sub.M 20, the Lost FES-C channel timeout (Nominally, for example, 10 secs), and T.sub.M 22, the Transmit inhibit timeout (1 superframe). The MET monitors the FES-C channel and generally only enables transmission if all the following conditions are true:

the MET is in receipt of the FES-C channel, indicated when timers T.sub.M 20, and T.sub.M 22 are not expired;

the MET is a member of the NET ID;

the Speaker ID is the vacant ID or is equal to the MET user's DN;

the user initiates PTT signaling.

The transmitting MET continues transmitting provided all of the following conditions are true:

the MET is in receipt of the FES-C channel, indicated when timers T.sub.M 20, and T.sub.M 21 are not expired. (T.sub.M 21 is defined in MET Call Supervision Procedure below);

the current speaker as saved by the MET (see below) matches the MET's DN; and

the PTT remains active.

The MET tests for a valid subframe at each FES-C subframe interval. When the MET receives a valid subframe, the MET restarts timers T.sub.M 20 and T.sub.M 22. A valid subframe is a voice subframe or a subframe having a message type recognized by the MET as a Net Radio message type and no errors are detected in the packet. If the subframe received is a voice frame, or a NR.sub.-- SU where the Speaker ID matches the MET's DN, (i.e. the MET is confirmed as the "speaker"), the MET restarts timer T.sub.M 21, "loss of speaker status timeout".

If the subframe received is a NR.sub.-- SU, the MET tests the NET ID. If the NET ID is not valid for the MET, the MET shall retune to the GC-S channel. If the NET ID is valid, the MET saves the Speaker ID as the current speaker. If the Speaker ID matches the MET's DN, the MET confirms, or maintains it's status as the "speaker". If the Speaker ID does not match the MET's DN, the MET ceases transmitting, if it was transmitting, and negates it's status as the speaker.

If the subframe received is a Net Radio Call Release (NRCR) SU, the MET ceases transmitting and retunes to the GC-S channel. On expiration of timer T.sub.M 22, the MET checks its speaker status. If the MET has the speaker status it ignores the timeout and continues transmitting. If the MET's speaker status is negated, it inhibits further PTT requests until all of the conditions listed above to enable transmission are satisfied.

On expiration of timer T.sub.M 21, the MET stops transmitting, and negates or clears it's status as the current speaker. The MET indicates to the user that transmission has ceased. The MET remains on the assigned Net Radio channel. On expiration of timer T.sub.M 20, the MET retunes to the GC-S channel.

MET Call Supervision Procedure

MET call supervision defines the procedures followed by a MET when the PTT button is pressed or released. The procedures, together with the FES Net Radio procedures provide contention resolution of the inbound channel. The MET accesses the MET-C channel for transmission when the PTT is activated by the user in accordance with the MET call monitoring specified above and the call supervision specified herein, and by the event tree given in FIG. 32.

To access the MET-C channel, the MET transmits a PTT.sub.-- SU using the In-band signaling mode for one frame as shown in FIG. 33 until an NR.sub.-- SU is received with the Speaker ID not equal to the vacant code. The PTT.sub.-- SU includes the MET user's DN and the NET ID. The MET then switches to voice mode and starts timer T.sub.M 23, the contention window timer (Nominally, for example, 1 second).

The MET continues transmitting on the MET-C channel and monitoring the FES-C channel. On detection of In-band signaling subframes with NR.sub.-- SUs, the MET tests the Speaker ID. If it matches the MET's DN, the MET saves the Speaker ID as the current speaker. The MET is then confirmed as the speaker. If the Speaker ID does not match the MET's DN, the MET ceases transmitting. The MET saves the Speaker ID as the current speaker. The MET negates or clears its speaker status.

If the MET detects voice mode subframes on the FES-C channel instead of In-band Signaling subframes, it assumes that these voice frames are either its own, or the dispatcher's and that the Speaker's ID SU was missed. In this case the MET continues transmitting. An NR-SU is sent to the MET in the next superframe. If an NR.sub.-- SU with the MET's DN as speaker ID is not received before the expiration of T.sub.M 23, the MET ceases transmitting. The MET then negates its speaker status.

When the MET is confirmed as the speaker, the MET starts timer T.sub.M 21, the Lost Speaker Status timeout (Nominally, for example, 3.5 secs). In addition the MET disables passing voice output to either the extended speaker or the handset speaker. The MET continuously transmits while the PTT button is active and conditions specified in the MET call monitoring procedures are met.

When the user releases the PTT button and the MET has been transmitting, the MET finishes transmitting any voice subframes remaining in the buffer, and then switches to In-Band signaling mode as shown in FIGS. 33 and 34. The MET transmits one frame using the In-band Signaling mode consisting of PTT.sub.-- SUs. The PTT.sub.-- SU identifies the MET user's DN and the NET ID and the PTT Release Code. The MET then ceases transmitting, but remains tuned to the net radio frequencies, and continues to monitor the FES-C channel for the NET ID in accordance with the MET call monitoring procedures. After the user releases the push to talk, the MET waits for a time equal to or greater than the delay time before enabling the loudspeaker again.

Call Release

Upon receiving the Net Radio Call Release SU, the MET tuned to the FES-C channel retunes to the GC-S channel and deactivates the Net Radio call indicator to the user. The FES operates a hangtimer. When no activity has occurred for the hangtime duration, the FES releases the call. The hangtimer, perceived by a MET user is shown in FIG. 35.

Private Mode Service Call Procedures

The Network Control System procedures for MET originated Private Mode Service calls allow mobile CUG members to originate a call using a Net Radio channel configuration for the purpose of private communications with another member of the CUG. More than one NRC may be configured at a FES using the same NET ID. This permits more than one Private Mode call to be in progress at the same time.

Channel Assignment

MET originated Private Mode service calls are established using the sequence of messages shown in FIG. 36. The protocol employed is as specified for Net Radio service in the event tree given in FIG. 29. On selection of Private Mode service, and on receipt of dialed digits, a MET, suitably equipped for Private Mode service formats and sends a Net Radio Access Request SU using MGSP on the MET-SR channel. The NRACR.sub.-- SU includes the NET ID private mode with the called DN. If no NET ID with a NET ID Tag number of `00 hex` has been assigned to the MET, the MET indicates call failure to the operator.

Upon receipt of the NRACR.sub.-- SU the GC performs all the verifications as specified for MET originated Net Radio service calls. Once the GC determines that the call can be completed it selects the frequency assignments required for the NET ID and formats a NRCHA.sub.-- SU with the call type field set for Private Mode and the MET FTIN number of the calling MET in place of the NET ID. The GC sends the assignment SU three times as for Net Radio service on the GC-S channel.

The GC formats a second Private Mode call type NRCHA.sub.-- SU using the called MET FTIN number in place of the NET ID. The GC sends this assignment SU three times as for Net Radio service on the GC-S channels required for the NET ID. In the event there are no NRC's available to handle the call, the GC sends a Call Failure Message with no resources as the cause indication to the requesting MET. Upon receipt of the NRCHA.sub.-- SU with the Private Mode call type, a MET compares it's FTIN with the FTIN in the NUCHA.sub.-- SU. If the numbers match, the MET tunes to the assigned frequencies. The MET then proceeds as for Net Radio service calls.

Call Establishment, Call Monitoring, Call Supervision and Call Release

The MET uses the call establishment, call monitoring, call supervision and call release procedures as specified for Net Radio service calls.

Priority 1 Service Call Procedures

The MET shall follow the Priority 1 procedures as specified in this section and as shown by the event tree given in FIG. 37. The MET supports a Priority One mode of operation called the normal mode.

Priority One Normal Operation

When the MET user initiates Priority 1 service, the MET takes one of three actions based on the state of the MET at the time. The three states are:

Case 1: Net radio call is not in progress.

Case 2: Net Radio call in progress and the current

Speaker ID is equal to the vacant code.

Case 3: Net Radio call in progress and the current

Speaker ID is not the vacant code.

Case 1

In the case where the Net Radio call is not in progress and the MET user has selected a Net ID, the MET originates the Net Radio Call. The MET appends the Priority 1 code to the Net ID in the NRACR.sub.-- SU. The Net ID included in the NRACR.sub.-- SU is that which the MET user has selected. The MET then proceeds with call establishment, call monitoring, call supervision, and call release as for MET originated Net Radio service.

Case 2

In this case the MET responds as in case 1, except that the NET ID included in the NRACR.sub.-- SU is retrieved from the NVRAM location specifically tagged by the MET user for this situation.

Case 3

In the case where the Net Radio call is in progress and the speaker ID is not the vacant code and not equal to the MET's DN, the MET tunes to the GC-S channel and sends a NRACR.sub.-- SU with the Priority 1 code appended to the Net ID as for Case 1.

In the case where the Net Radio call is in progress and the speaker ID is not the vacant code but is equal to the MET's DN, the MET sends a PTT.sub.-- SU request with the Priority One code appended.

Upon receipt of the NRACR.sub.-- SU, the GC follows the call setup procedures as for MET originated Net Radio Calls. The GC rebroadcasts the NRCHA.sub.-- SU on all GC-S channels identified in the Net ID or that are active (per dynamic beam allocation). The GC sends the NRCHA.sub.-- SU three times in three consecutive superframes as for Net Radio Service channel assignments. The GC sets the Priority 1 code and includes the call identifier of the established call in the GC-I channel assignment message to the FES.

The requesting MET tunes to the assigned frequencies and proceeds as for MET originated Net Radio calls. The MET presently transmitting on the MET-C channel detects that the speaker ID no longer matches its DN and ceases transmitting in accordance with the MET call monitoring procedures. The Priority 1 requesting MET then proceeds as for Case 1.

Priority One Default Operations

When the MET user initiates Priority One Default service via the Priority One button, the MET expediently performs the following actions:

The MET tunes to the GC-S channel and sends a NRACR.sub.-- SU with the Priority One code appended on the corresponding MET.sub.-- SR channel.

The MET retrieves the NET ID included in the NRACR.sub.-- SU from a NVRAM location specifically tagged by the MET user for this situation.

Upon receipt of the NRACR.sub.-- SU, the GC follows the call setup procedures as for MET originated Net Radio Calls. The GC rebroadcasts the NRCHA.sub.-- SU on all GC-S channels identified in the Net ID or that are active (per dynamic beam allocation). The GC sends the NRCHA.sub.-- SU three times in three consecutive superframes as for Net Radio Service channel assignments.

The GC sets the Priority 1 code and includes the call identifier of the established call in the GC-I channel assignment message to the FES.

The requesting MET tunes to the assigned frequencies and proceeds as for MET originated Net Radio calls. If the Net ID selected for Priority One default operations is in use and the Speaker ID is not vacant, the MET transmitting on the MET-C channel detects that the Speaker ID no longer matches its DN and ceases transmitting in accordance with MET call monitoring procedures.

The MET proceeds with call establishment, call monitoring, call supervision and call release as for MET originated Net Radio service.

NET Radio Security Generation and Verification Process

The MET beneficially includes the option of providing the service with a verification process that utilizes a security code. The security code NET ID ASK is stored in the MET memory as encrypted. The MET recovers or derives the Net ID ASK from the encrypted Net ID ASK using the following process illustrated in FIG. 38.

The 64-bit MET ASK and the concatenation of the 24 bit MET electronic serial number (ESN) and 10 "A" hexadecimal fill digits to form a 64-bit word are input into the DES encryption process. Both the MET ASK and the DES encryption process are described in detail in copending patent applications entitled "Fraud Detection and User Validation System for Mobile Earth Terminal Communication Device," to William R. Tisdale and C. Edward Sigler, application serial number 08/565,036 filed on Nov. 30, 1995, and application serial number 08/601,912 filed on Feb. 15, 1996, both of which are incorporated herein by reference. A description is also provided hereinafter.

For the basic fraud detection and user validation system, the following process is implemented. A MET authenticates its identity upon each commissioning event, performance verification event, and call setup event. The authentication process is based upon the use of an encryption function and a MET Access Security Key (ASK) to form an authorization code (the Access Security Check Field) from a random variable (the MET transmit and receive frequency assignments) at the beginning of each event.

The encryption algorithm is preferably the Data Encryption Standard (DES) defined by ANSI X3.92-1981/R1987, used in the Electronic Codebook Mode (ECB) and is built into both the MET and the NCC. The ASK for each MET is generated by the MSS system operator. FIG. 39 illustrates the ASK generation process using a Seed ASK (SASK) provided by the MSS system operator, and a random number (EFTIN). The CRC-8 parity check algorithm is used to protect the integrity of the ASK. The parity check is generated over all of the hexadecimal digits comprising the ASK. The NOC provides a logically separate master database for the METID numbers (the MET electronic serial numbers) and the MET ASKs. The NCCs maintain slave ASK databases, and also provide protection from access by NCC processing functions other than the legitimate authorization processes.

The MET SASK is supplied to the MET user prior to commissioning. The MET provides a "user friendly" means, using alphanumeric prompted, audible tones, and key strokes, for the user to enter the SASK into the MET and verify its correctness. The MET verifies the correctness of the SASK via the CRC-B parity check. The MET uses the process detailed in FIG. 39 to generate the ASK from the inputted SASK. The MET stores the ASK in NVRAM. There is no means provided to read out or display the ASK once it is entered. Any attempted access to the ASK will preferably render the MET inoperable. It is possible, however, to enter or reenter the SASK at will.

For either MET originated or terrestrial network originated calls, the NCC compute a 64-bit cipher text block by using the ASK stored in its secure database and the DES algorithm in the ECB mode to encode a 64-bit input variable comprised of the 16-bit receive frequency assignment in the least significant bit positions, the 16-bit transmit frequency assignment in the next least significant positions, the 24 Access Security Fill Bits, and the 8 most significant positions filled with the hexadecimal "A" (1010) characters. The most significant 32 bits of the resulting cipher text block are designated the Access Security Check Field (ASCF). The least significant 32 bits are designated the Secondary Security Check Field (SSCF). The Access Security Check Field and the Secondary Security Check Field generation process is depicted in FIG. 40. The Access Security Check Field is transmitted from the GC to the terminating FES in the SU.

The MET independently generates the Access Security Check Field using an identical process to encode the transmit and receive frequency assignments received in the MET Channel Assignment SU received from the NCC. Following the establishment of the MET-FES communication link, the MET transmits the Access Security Check Field to the FES in the scrambling Vector SU.

The FES compares the MET and NCC generated Access Security Check Fields on a bit-by-bit basis. If the values are identical, the MET is declared authenticated, and the call setup is completed normally. If the values are not identical, the MET identity is declared non-authenticated, and the FES terminates the call process. The FES sends a channel release message to the NCC, as well as the call record, with authentication failure indicated as the call clearing reason.

During commissioning or PVT, the MET generates the Access Security Check Field from the transmit and receive frequency assignments included in the Set Loopback Request SU received from the NCC, and returns it to the NCC in the scrambling vector SU. The NCC compares the locally generated value of the Access Security Check Field with the value returned by the MET on a bit-by-bit basis. If the values are identical, the MET identity is declared authenticated, and commissioning or PVT continues. If the values do not compare, the MET identity is declared non-authenticated, and the NCC terminates the process, declare PVT failure, and sends an authentication failure alert message to the NOC.

A "clear mode" is provided to facilitate system troubleshooting on an individual MET basis. This mode is invoked at the NCC (with suitable password control), and causes the authentication system to accept and complete all calls for the specific MET, with or without a valid Access Security Check Field.

An "override mode" is provided that permits system operation without authentication, in case of failure or other problems. This mode is invoked at the NCC through operation of a hardware or software switch, with suitable protection (i.e., physical key, password).

The "Authentication Subsystems" at the NOC (which maintains the master MET ASK database), and at the NCC (which maintains the slave MET ASK database and generates the Access Security Check Field) are preferably both logically and physically separated from other NOC and NCC processors, and provide both physical and password security to prevent unauthorized access to the MET ASK databases. The NCC processors access the NCC Authentication Subsystem with the MET ID and the transmit and receive frequency assignments, and the NCC Authorization Subsystem returns only the MET ID and the Access Security Check Field.

A MET generally authenticates its identity upon each commissioning event, performance verification event, and call setup event. The authentication process is based upon the use of an encryption function and MET Access Security Key (ASK) to form an authorization code (the Access Security Check Field) from a random variable (the MET transmit and receive frequency assignments) at the beginning of each event.

The encryption algorithm is preferably the Data Encryption Standard (DES) defined by ANSI X3.92-1981/R1987, used in the Electronic Codebook Mode (ECB), and is built into both the MET and the NCC. DES is well known, well documented, and is in the public domain. Its performance is also well known, and is generally approved for U.S. Government application. The algorithm is defined in Federal Information processing Standard (FIPS) Publication 46-1, 15 Jan. 1977, Reaffirmed 22 Jan. 1988 (Approved as American National Standard X3.92-1981/R1987), incorporated herein by reference. While a purely software implementation of DES would require significant processing power for a continuous stream encryption, we have discovered that for the MET, only the generation of a single "codeword" is needed. Thus, for the MET system, the software implementation is feasible and not processing intensive. Additional discussion of the DES algorithm can be found in the following references, all of which are incorporated by reference herein: Federal Information Processing Standards Publication 74, 1 Apr. 1981; Federal Information Processing Standards Publication 81, 2 Dec. 1981; Robert V. Meushaw, "The Standard Data Encryption Algorithm, Part 1: An Overview", BYTE Magazine, March 1979; and "The Standard Data Encryption Algorithm, Part 2: Implementing the Algorithm", BYTE Magazine, April 1979.

The following relates to an enhanced or more detailed version of the fraud detection and user validation process. The ASK for each MET is independently generated at both the MET and the NOC/NCC using the DES algorithm. The inputs to the generation process is a Seed ASK (SASK) provided by the MSS system operator, and a random number (EFTIN KEY) generated by the MET at the time of commissioning and used to encrypt the FTIN. The SASK for each MET will be generated by the CMIS at the time of MET registration. As indicated above, FIG. 39 illustrates the ASK generation process using the SASK and EFTIN variables. A standard CRC-8 parity check algorithm will be used to protect the integrity of the SASK. The parity check is generated over all of the hexadecimal digits and incorporated into the SASK.

The NMS provides the processing capability necessary to generate the SASK and any needed parity check. Note that inclusion of the parity check bits as part of the SASK yields a 64 bit binary word which is the length of key required by the DES. The SASK parity check sequence is generated by the polynomial G(X)=X.sup.8 +X.sup.7 +X.sup.4 +X.sup.3 +X+1. The input to the parity checker is the information portion of the SASK. The SASK is supplied to the MET subscriber prior to commissioning. The key distribution scheme is not a requirement of this specification. The MET provides a "user friendly" means, using alphanumeric prompts, audible tones, and key strokes, for the user to enter the SASK into the MET. The MET verifies the correctness of the SASK as described below. If the SASK is incorrect, the user is prompted to enter the SASK again. The MET does not enter the "Ready for Commissioning" state prior to entry of a valid SASK.

At the time of commissioning, the MET uses the DES algorithm in the ECB mode to generate the "active" ASK. The EFTIN KEY is extended to additional bits by filling the leading positions and is used as the plain text input to the algorithm. The SASK is used as the key. The resulting cipher text block is from the ASK. The forms of the elements used in the key generation process are shown in FIG. 39. It is impossible for the MET to initiate recommissioning either with or without reentry of the SASK. Importantly, the CGS can selectively command at will a MET that has been detected as potentially fraudulent to reinitiate the commissioning process, thereby creating a new ASK and CCV. Therefore, if a fraudulent MET has gained access to CGS, the CGS can selectively "remove" the fraudulent MET upon detection. The MET stores the SASK and the ASK in NVRAM. There is no means provided to read out or display either the SASK, or the ASK once it is generated and stored.

The keying process is illustrated in FIGS. 41A-41C. FIG. 41A is a flow chart of the keying process, FIG. 41B is an illustration of the keying process in the satellite communication system, and FIG. 41C is a signal/data diagram of the keying process. In FIG. 41A, the MET subscriber registers or requests to become a subscriber of the satellite communication system in step S2. Registration information is sent to CMIS and a customer service representative enters the registration information in the CMIS system that handles subscriber billing, contact and the like, in step S4. CMIS then generates the Seed ASK which is supplied to the NOC/NCC and the subscriber/distributor of the MET prior to commissioning in step S6. The subscriber/distributor enters the SASK into the MET in step S8, and the MET stores the SASK for commissioning in step S10.

The NOC/NCC stores the ESN and SASK and assigns a Forward Terminal ID (FTIN) for each MET in step S12. The NOC/NCC also receives an FTIN Key from the MET which is a random number generated by the MET when the MET requests to be commissioned, and uses the FTIN key and the SASK to generate the ASK in step S14. The NCC stores the ASK in step S16. The NCC uses the FTIN Key and the FTIN to generate the EFTIN in step S18 and transmits the EFTIN to the MET. The MET uses the EFTIN and the FTIN key to recover the FTIN in step S20. The MET also uses the SASK and the FTIN Key to generate the ASK in step S20. The MET then stores the ASK and FTIN in step S24 to be used later during the registration or call connect process. The commissioning process is then completed in step S26, providing the necessary security codes in the MET associated with a specific ESN and in the NCC/NOC. Also, at the time of MET commissioning, the NCC duplicates the process of MET ASK generation. The NCC process is entirely automatic, and is protected from access by, the MSS system operators.

The NCC computes a cipher text block (see FIG. 40) by using the ASK stored in its secure database and the DES algorithm to encode an input variable comprised of the receive frequency assignment in the least significant positions, the transmit frequency assignment in the next least significant positions, the Access Security Fill Bits (transmitted in the Bulletin Board, see, for example, FIG. 42), and the most significant positions filled with predesignated characters. The 32 most significant bits of the resulting cipher text block are designated the Access Security Check Field, and the least significant is designated the Secondary Security Check Field. The MET also generates the Access Security Check Field from the transmit and receive frequency assignments included in the Set Loopback Request SU received from the NCC, and returns it to the NCC in the scrambling vector SU. The NCC compares the locally generated value of the Access Security Check Field with the value returned by the MET on a bit-by-bit basis. If the values are identical, the MET identity is declared authenticated, and commissioning or PVT continues. If the values do not coincide, the MET identity is declared non-authenticated, and the NCC terminates the process, declares PVT failure, and sends an authentication failure alert message to the NOC.

As illustrated in FIG. 38, the MET ASK is the DES `key` and the concatenation of the ESN and fill bits is the DES `Plaintext`. The least significant 16-bits of the resultant cryptovariable is then exclusive-"or"-ed with the encrypted Net ID ASK to form the cleartext Net ID ASK that is stored in the NVRAM of the MET.

Once the MET has derived the NET Radio (NR) ASK, the MET then proceeds to determine the scrambling vector used to initiate the MET scrambler for NET Radio calls. The generated NET Radio scrambling vector is applied to both the MET transmit and receive scrambling units. The MET determined the NR scrambling vector using the following process.

As illustrated in FIG. 43, the 16-bit MET Transmit and Receive frequency assignments are concatenated with 8 "A" hexadecimal fill digits. This concatenated array is used as the "Plaintext" input to the DES process. The NET Radio ASK is also concatenated with 12 "A" hexadecimal fill digits. This second concatenated array is used as the "Key" input to the DES process. The NET Radio scrambling vector is, for example, the 15 least significant bits of the resultant 64-bit DES "ciphertext" output therefrom. When a MET wants to join a NET Radio group, then the MET is able to enter the group via the scrambling vector.

Dual Standby Operation

The MET includes the capability of dual standby operation when configured, registered and commissioned for both MTS and NR service. Dual standby operation is defined as MET operation whereby the MET responds to either MTS page requests or NR Channel Assignments as transmitted on the GC-S channel. To effectuate the dual standby operation, the MET is not required to monitor the GC-S channel for service requests of another type while the MET is responding to a service request of either type. This feature is user selectable: either MTS only, NR only, or Dual Standby. The MET, of course, determines whether an MTS call or NR call is desired via the appropriate entries by the MET user or by receiving the appropriate signaling units discussed previously.

When the "MTS only" of the dual standby mode feature is selected, the MET will undertake the authentication process after the MET ASK has been generated. The authentication process indicates that the MET is ready to gain access to CGS for voice/data communication using the real-time authentication process described hereinafter. According to the authentication process, the Access Security Fill Bits are transmitted in the MET bulletin board. The NOC operator can manually change this field to any desired pattern. It is recognized that when the Access Security Fill Bits are changed there will be a short period during which METs will attempt to access the system with Authentication Codes generated using the "old" fill bits, which may result in those METs being denied service. As one option to prevent this problem, the NOC operator will have the option to disable the access security check for a short time when the fill bits are changed. The NCC computes a cipher text block (see FIG. 40) by using the ASK stored in its secure database and the DES algorithm to encode an input variable comprised of the receive frequency assignment in the least significant positions, the transmit frequency assignment in the next least significant positions, the Access Security Fill Bits (transmitted in the Bulletin Board, see, for example, FIG. 42), and the most significant positions filled with predesignated characters. The 32 most significant bits of the resulting cipher text block are designated the Access Security Check Field, and the least significant is designated the Secondary Security Check Field. The Access Security Check Field and the Secondary Security Check Field are transmitted to the terminating FES in the Channel Assignment SU.

The MET independently generates the Access Security Check Field and the Secondary Security Check Field using an identical process to encode the transmit and receive frequency assignments received in the MET Channel Assignment SU received from the NCC. Following the establishment of the MET-FES communication link, the MET transmits the Access Security Check Field in the Scrambling Vector SU.

The FES compares the MET and NCC generated Access Security Check Fields on a bit-by-bit basis. If the values are identical, the MET identity is declared authenticated, and the call setup shall be completed normally. If the values are not identical, the MET identity is declared non-authenticated. If nonauthenticated, the FES terminates the call process, and sends a channel release message to the NCC with authentication failure indicated as the call clearing reason. Upon receiving the channel release message with authentication failure as the call clearing reason, the GC generate an authentication failure event. The NCC treats this as an alarm condition. The NCC provides a real time display to the MSS operator console indicating that the call was failed due to authentication failure.

A "clear mode" is provided to facilitate system troubleshooting on an individual basis. This mode is invoked at the NCC (with suitable password control), and causes the authentication system to accept and complete all calls for the specific MET with or without a valid Secondary Security Check Field.

An "override mode" is also provided which permits system operation without authentication, in case of failure or other problems. This mode is invoked at the NCC through operation of a hardware or software, with suitable protection (i.e., physical key, password).

An option is provided in which the "Authentication Subsystem" at the NOC/NCC (which maintains the MET ASK database) is both logically and physically separated from mother NOC and NCC processors, and which provides both physical and password security to prevent unauthorized access to the MET ASK databases. The NCC processors access the NCC Authentication Subsystem with the MET ESN (RTIN) and the transmit and receive frequency assignments and fill bits. The NCC Authorization Subsystem returns only the MET ESN, the Access Security Check Field and the Secondary Security Check Field.

A MET is required to authenticate its identity upon each request to invoke an advanced calling feature which redirects the source or destination of a call or adds participants. To effectuate authentication, the MET includes the least significant ("right most") bits of the Secondary Security Check Field in the AFR SU ("Hook Flash") transmitted in an Advanced Features Request Sequence. The serving FES compares the these least significant bits of the Secondary Security Check Field received from the NCC in the Channel Assignment SU. If the values are identical, the MET identity is declared reauthenticated, and the advanced features request is processed normally. If the values are not identical, the MET identity is declared non-reauthenticated, and the FES denies the advanced features request, and provides a suitable indication, such as a tone or recorded voice announcement, to the MET subscriber. The FES sends a reauthentication failure alert message to the NCC.

The MSS system provides for a Call Count Variable (CCV) in the authentication process. The CCV is a count of calls made by each MET, and is separately and independently maintained by the individual METs and the NCC. The CCV is a 16 bit binary number, and is set equal to the value of the least significant 16 bits of random EFTIN KEY when the MET is commissioned or recommissioned. The CCV is incremented at the completion of each call setup. The CCV is also incremented at the MET when the change from transmission of the Scrambling Vector SU to voice/data frames is made. The CCV is also incremented at the NCC when the call Setup Complete SU is received from the serving FES.

At the time of call initiation, the NCC adds (i.e., the logical XOR operation) the CCV to the least significant bits of the Secondary Security Check Field. The resulting CCV Check Field is included in the Channel Assignment SU sent to the serving FES. The MET independently generates a CCV Check Field using an identical process, and includes the result in the Scrambling Vector SU sent to the serving FES during call setup.

The FES verifies the MET CCV. The FES declares the CCV to be authenticated if the absolute value of the error is equal to or less than a configurable threshold. Provision is made for selection of the error threshold by the NOC/NCC operators. The nominal value of the threshold is zero, and the range is at least zero to 15 (decimal). If the absolute value of the error is greater than the threshold, the FES declares the CCV non-authenticated. The FES terminates the call process, and sends a channel release message to the NCC, with CCV authentication failure indicated as the call clearing reason. Upon receiving the channel release message with authentication failure as the call clearing reason, the GC generates an authentication failure event. The NCC treats this as an alarm condition. The NCC provides a real time display on the MSS operator console indicating that the call was failed due to authentication failure. FIGS. 44A and 44B are diagrams of this described authentication process using the authentication security key generated by the process described in FIGS. 41A-41C.

Advantageously, the fraud detection and user validation system optionally includes an enhanced MET authentication process through the use of a Personal Identification Number (PIN) entered by the MET subscriber at the initiation of each call. The PIN is not to be used for MET terminated calls. The PIN is provided to the MET subscriber by the MSS operator and must be entered whenever the MET initiates a call. The NOC/NCC makes provision to enter and store the PIN in the MET ASK secure database.

The NOC/NCC software architecture makes provision for a "PIN REQUIRED" Flag to be included in the data base for each MET, and in the calling sequence and software used to invoke generation of the Access Security Check Field by the Authentication Subsystem. The PIN Required flag can be set by CMIS or the NOC operator. If the use of the PIN is required, the NCC authentication subsystem replaces the most significant Access Security Fill Bits with the PIN characters. Generation of the cipher text block comprising the Access Security Check Field and the Secondary Security Check Field and subsequent actions is then proceeded as described above.

Generation of the cipher text block comprising the Access Security Check Field and the Secondary Security Check Field and subsequent actions is then performed as described above. The form of the "plain text input" used in the PIN-inclusive ASCF generation process is shown in FIG. 45. Transmission and verification of the various Security Check Fields, and subsequent actions, is implemented as described above.

When the "NR only" of the dual standby mode feature is selected, the MET undertakes the authentication process if it is the initiator of the NR call, or generates a scrambling vector for the NET Radio service using the MET ASK and the NR ASK to join the NET group.

When the "Dual Standby" of the dual standby mode feature is selected, the MET will undertake either the authentication process indicating that the MET is ready to gain access to CGS for voice/data communication or the scrambling vector generation process indicating that the MET is ready to gain access to a NET Radio group. As soon as the MET dedicates itself for one of the MTS or NET Radio services, then the MET is generally no longer able to receive the other service, with the exception of receiving preferably a unique tone indicating that a call on the other service is waiting, i.e., a modified call waiting feature. In this manner, the MET is able to advantageously utilize both the standard MTS voice service and the NET Radio service.

Although a number of arrangements of the invention have been mentioned by way of example, it is not intended that the invention be limited thereto. Accordingly, the invention should be considered to include any and all configuration, modifications, variations, combinations or equivalent arrangements falling within the scope of the following claims.

Actual GSI

Definition: Current GSI based on TDM changes during MET operation. This field is populated by the NOC based on actions on the CGS. The CMIS cannot create or update this field.

Call Barring Inbound/Outbound Flag

Definition: Describes the call barring entry as applying to incoming or outgoing calls. If the Call Barring List is flagged as inbound, it applies to calls the MET is receiving. If the Call Barring List is flagged as Outbound, it applies to calls the MET is making.

Call Barring Include/Exclude Flag

Definition: Describes the call barring entry as an included (legal) call or an excluded (illegal) call. When a Call Barring List is flagged as include, the MET may only make calls to the numbers or NPAs on the list. Any other call would be denied. Conversely, if a Call Barring List is flagged as Exclude, the MET may make calls to any number or NPA except those on the list.

Call Barring List Value

Definition: Numbering plan area or phone number in the call barring list. The values that appear in the list are the phone numbers or NPAs that the MET's restriction apply to. The types of restrictions are dictated by the flags for Include/Exclude and Inbound/Outbound Call Barring.

Call Trap Flag

Definition: Indicates call trapping has been initiated for the MET. The GC will trap MET states as they change during MET CGS activity. This information will be provided to the CMIS on a call record.

Call Type

Definition: Service available on the MET. There are four service types: voice data (2400 or 4800 baud), fax, and alternate voice data (avd). For each service the mobile is registered, a service record is created with a single call type indicated. This call type in turn has a unique mobile identification number (min) associated with it.

Carrier

Definition: Name of preferred IXC carrier. This field is a switch field used to support equal access to long distance carriers.

Cellular ESN

Definition: 32 bit ESN that is used by the switch. For dual mode cellular/satellite phones it is the ESN for the cellular portion of the phone and would match the ESN used by the home cellular carrier to identify that mobile terminal.

CGS Time Stamp

Definition: Time stamp was created/modified. Part of the notification of success or failure of CGS action. Not created or updated by CMIS.

Channel Spacing

Definition: Multiple of frequency step size. This element is a characteristic of the MET Class. CMIS will only have the MET Class ID that a particular METs equipment maps to. NE originates this and other data that describes the MET Class and sends it to the NOC.

Check String

Definition: Constant used by the GC to validate the encryption/decryption algorithm. This element is related to the ASK.

Commanded GSI

Definition: Set by CMIS this is the original GSI stored as a NVRAM (non-volatile RAM) parameter by the MET. Required for each new MET registered for service. This element is used by the MET to tune to a GC-S channel during commissioning on the CGS. Without the GSI the MET is incapable of logging on to the CGS.

Configuration File

Definition: A file containing the contents of a working configuration that has been saved to disk under a unique name.

Current Configuration

Definition: The set of resources that exist in the configuration most recently sent to or received from the NOC. This is assumed to be the actual configuration of the traffic bearing network at any given time.

Commit a Resource

Definition: Explicit engineer action to add a fully provisioned interim resource to the working configuration.

Control Group ID

Definition: The CGS is divided into Control Groups that contain circuit pools, signaling channels, bulletin boards, METs, and VNs. A MET may only belong to one Control Group. The control Group assignment is based on the virtual network membership. All VNs a MET is a member of must be in the same control group.

Cust Group

Definition: Identifier for a specialized routing information used at the switch (e.g., 1024 available cust groups per MSR). Dialing plans will be implemented for groups of customers through a Customer Group (Cust Group).

Data Hub Id

Definition: Used to route messages during PSTN to IVDM call setup to the proper data hub. This is only applicable for METs that are participating in the Mobile Packet Data Service.

Date Last Tested

Definition: Time stamp of most recent commissioning test. This field is populated by the NOC and cannot be created or updated by CMIS.

Default VN

Definition: VN selected if user does not specify VN during dialing. For METs that belong to only one VN, this can be populated with the VN ID the MET is assigned to by default.

EIRP

Definition: Equivalent Isotropic Radiated Power--power level required for a MET to receive a satellite signal. This element is a characteristic of the MET Class. CMIS will only have the MET Class ID that a particular METs equipment maps to. NE/SE originates this and other data that describes the MET Class and sends it to the NOC.

Event Argument Id

Definition: Part of the Event Record received from the NOC. CMIS has no part in creating or updating events--they arrive unsolicited from the NOC.

Event Argument Type

Definition: Part of the event Record received from the NOC. CMIS has no part in creating or updating events--they arrive unsolicited from the NOC.

Event Argument Value

Definition: Part of the Event Record received from the NOC. CMIS has no part in creating or updating events--they arrive unsolicited from the NOC.

Event Argument VMS Type

Definition: Part of the Event Record received from the NOC. CMIS has no part in creating or updating events--they arrive unsolicited from the NOC.

Event Code

Definition: Part of the Event Record received from the NOC. CMIS has no part in creating or updating events--they arrive unsolicited from the NOC.

Event Severity

Definition: Network impact assessment of the trouble event.

Event Time

Definition: Time the event occurred within the network.

Event Type

Definition: Part of the Event Record received from the NOC. CMIS has no part in creating or updating events--they arrive unsolicited from the NOC.

External Date Time Stamp

Definition: CMIS generated time stamp used for CMIS audit purposes in exchanging messages with the CGS.

External Transaction Id

Definition: CMIS generated transaction id used for CMIS audit purposes in exchanging messages with the CGS.

Feature Set

Definition: Identifies MET features within a specific VN. Fixed features are set up during order processing and require no action by the MET user to invoke a feature. MET activated features must also be set up during order processing but will only be available through some action on the part of the MET use during call process.

Fixed Features Include

Calling Line Id Presentation (CLIP)--display the calling party's number to a MET.

Calling Line Id Restriction (CLIR)--prohibition from displaying the METs number when it is calling another party.

Connected Line Id Presentation (COLP)--display the number the calling MET is connected to.

Connected Line Id Restriction (COLR)--prohibit display of the connected MET's number to the calling party.

Sub-addressing (SA)--allows one or more attachments to the MET to be addressed. This is being accomplished through unique phone numbers for service types requiring different equipment.

Call Waiting (CW)--notification to a MET engaged in the call that another call is waiting. MET may accept the other call or ignore it.

Call Barring (CB)--restricts the MET user's from making or receiving one or more types of calls.

Operator intervention (OI)--allows an operator to break into a call in progress for the MET.

Operator Assistance (OA)--allows the MET to access an MSAT operator to receive assistance

Call Priority (CP)--used in conjunction with the system's call queuing function (trunk access priority) presence of this feature gives a MET access to channels at times of congestion ahead of MET's with lower priority. Priority applies only to MET initiated calls.

MET Activated (Dynamic) Features Include

Call Transfer (CT)--allows sa MET user to transfer an established call to a third party.

Call Forwarding Unconditional (CFU)--permits a MET to have all calls forwarded to another MET or PSTN number.

Call Forwarding Busy (CFB)--permits a MET to have all incoming calls attempted when the MET is busy to another MET or PSTN number.

Call Forward Congestion (CFC)--permits the MET to have all incoming calls attempted when the signaling channels are congested answered with a recorded announcement intercept.

Call Forward No Reply (CFN)--permits a MET to have all incoming calls attempted when the MET is not answering to another MET or PSTN number. This applies if the MET is blocked, turned off or not answering.

Call Holding (CH)--allows a MET to interrupt call communication on an existing connection and then re-establish communications.

Alternate Voice Data Operation (AVD)--allows a MET user to toggle between voice and data mode during a call. Requires that the call be initiated in voice mode. Only the MET user may toggle between voice and data. This requires a special service type in addition to the activation at set-up of the feature.

Conference calling (CC)--allows a MET to communicate with multiple-parties including METs and PSTN concurrently.

Three Party Service (3PS)--allows a MET to who is active on a call to hold that call, make an additional call to a third party, switch from one call to the other (privacy being provided between the calls) and/or release one call and return to the other.

Malicious Call Trace (MCT)--enables an MSAT operator to retrieve the complete call record at a MET's request for any terminated call in real-time. The operator can then identify the calling party to the MET and take appropriate action.

Voice Mail (VM)--allows call forwarding to a voice mail box and retrieved of messages by the MET.

Alternate Accounts Charging (ACC)--allows the MET user to enter in an account code to charge the call to after entering the dialed digits

Fully Provision

Definition: Supply values to all attributes of a resource

Frequency Step Size

Definition: Minimum tuning increment acquired for a MET to tune in an assigned channel. CMIS will only have the MET Class ID that a particular MET's equipment maps to. NE originates this and other data that describes the MET Class and sends it to the NOC.

From MET Call Barring Flags

Definition: Describe actions available to a user originating a call from a MET. These call Barring flags relate to specific types of calls at an aggregate level to indicate if the MET can make or receive a call of a particular type. When this list indicates that an Inclusion or Exclusion to particular numbers or area codes is allowed, the values for those restrictions are indicated on a Call Barring List.

FTIN

Definition: Forward Terminal Identification Number--Downloaded to MET from NOC during commissioning. Used for MET to GC signaling.

Internal Data Time Stamp

Definition: NOC generated time stamp used for NOC audit purposes.

Internal Transaction Id

Definition: NOC generated transaction is used for NOC audit purposes.

Interim Resource

Definition: The resource currently being modified by the engineer. Changes made to an interim resource are not added to the working configuration until the resource is committed to the working configuration

L Band Beam

Definition: Current beam MET is logged into. Determined by the GC during commissioning. CMIS has no role in creating or updating this field.

LCC

Definition: Line Class Code--type of phone, required by the switch.

MCC Class Id

Definition: Part of the Event Record received from the NOC. CMIS has no part in creating or updating events--they arrive unsolicited from the NOC.

MCC Instance

Definition: Part of the Event Record received from the NOC. CMIS has no part in creating or updating events--they arrive unsolicited from the NOC.

MCC Instance Id

Definition: Part of the Event Record received from the NOC. CMIS has no part in creating or updating events--they arrive unsolicited from the NOC.

MCC Instance Type

Definition: Part of the Event Record received from the NOC. CMIS has no part in creating or updating events--they arrive unsolicited from the NOC.

Message Status 1

Definition: Used in the message initiated by the NOC to acknowledge success or failure of a previously transmitted CMIS request. Used by the DM.

Message Status 2

Definition: Used in the message initiated by the NOC to acknowledge success or failure of a previously transmitted CMIS request. Will be used by the DM.

Message Verb

Definition: Action required at the NOC on data passed in a message from CMIS. This field is in the message relaying the results of a CMIS request.

Modulation Scheme

Definition: Non-standard modulation schemes. CMIS will only have the MET Class ID that a particular MET's equipment maps to. NE/SE originates this and other data that describes the MET Class and sends it to the NOC.

MSA

Definition: Mobile Servicing Area--identifies the last call's servicing area. Atomic data element within MSR. Transient data maintained in call processing not on the cellular switch table. Same as MSR.

MSR

Definition: Mobile Servicing Region id (table) contains multiple MSA assignments for the MET. For a roamer, the operator will input the MSR for temporary assignment. Allows up to 1024 cust groups--At CGS startup there will be 1 MSR.

MET ASK

Definition: Access Key MET must match during call setup/validation.

MET Class ID

Definition: Identifies the operating characteristics of the MET. Associated to MET by CMIS during registration from data supplied by NE/SE. The technical characteristics the MET Class ID encompasses are not needed by CMIS. These are stored on a table in the NOC and referenced by having the ID on the MET Information record. This ID applies to MET level regardless of how many services, etc. the MET has tied to it.

MET Commanded State

Definition: Current CGS status of MET.

MET Fraud Flag

Definition: indicates fraud has been detected on the MET. Updated by GC and CMIS only. This field is set at the MET level regardless of the number of services, etc. the MET has.

MET ID

Definition: CMIS assigned unique MET identifier. This can be a unique random number assigned to each MET registered for service. This is a MET level characteristic set once for the MET regardless of how many services, etc. the MET has. The MET ID is used by the NOC to identify METs. It does not have to be used within CMIS as a key field. MET ID cannot be updated once it has been assigned. A MET that requires a new MET ID for any reason would have to go through the registration process anew.

MET Signaling Code

Definition: Dialed digits from MET that identifies VN selection. Signaling codes would be assigned when a MET has multiple Virtual Network memberships. After the MET user enters the destination phone number, the pound key is hit and then the signaling code is entered if the caller wants to associated the outbound call with a particular virtual network. When no signaling code is entered, implies default VN be associated with the call.

Net Radio Monitor Code

Definition: Controls MET responses to specific channels after hang time limit is exceeded. A NR Net selection is made at the MET by the user.

Net Radio MET Directory Number

Definition: Net radio MET directory number. Assigned during registration.

Net Radio Net Id

Definition: Net ID

Net Radio MET Directory Number

Definition: Tag number on the MET equipment that identifies a particular net radio net.

Pending NVRAM Init Flag

Definition: Instructs the GC to download/initialize parameters for a MET.

Pending PVT Flag

Definition: This flag indicates that a PVT is required following next MET access. If CMIS requests a PVT to help diagnose customer troubles, an update would be sent to NOC with the Flag set to Perform PVT after Next MET access (1).

Picsel

Definition: Flag indicating if user has asked for a preferred IXC carrier. Carrier name is contained in CARRIER field.

Record Type

Definition: Type of record defined by object. Part of the Update Results Record.

Remote

Definition: Remote user--not required by the switch for MSAT Application.

Recent Configuration Event

Definition: This is a serial list of events received from the NOC that pertain to configuration database changes.

Referential Integrity

Definition: Database "key field" relationships that bind record within the databases, and create dependencies for additions and deletions of table instances.

RF Pin

Definition: Remote feature personal identification number. A user is prompted for a pin when attempting to use a remote feature.

Roam

Definition: Roam Capable--not required by the switch for MSAT Application.

RTIN

Definition: Reverse Terminal Identification Number which is also the satellite electronic serial number on satellite only and dual mode cellular/satellite METs. This is a unique identifier assigned by manufacturer for each piece of equipment. Within CGS processing the RTIN is used by the GC to signal the MET.

Satellite Id

Definition: Satellite Id of current L-band beam. The NOC populates this field based on MET commissioning. CMIS does not ever create or update this field.

SCM

Definition: Station Class Mark.

Secure Disable Flat

Definition: Channel Unit security check flag. Setting this flag to bypass security would disable ASK verification during call processing for a MET. CMIS cannot change this flag.

Signaling Priority

Definition: Number of MET signaling requests to the GC during network congestion. Assigned at the MET level--each MET may have only one signaling priority regardless of the number of VN memberships it has. The highest priority level is 0 and the lowest is seven.

TDM Change Enable Flat

Definition: Restriction on MET from changing TDM (TDM is the GSI)

Telephone Number

Definition: Phone number associated with a call type (voice, data, fax, avd) in a given virtual network.

Template

Definition: An initial set of default attribute values for each resource being added.

To MET Call Barring Flags

Definition: Describes actions available to a user receiving a call at their MET.

Trunk Access Priority

Definition: Satellite trunk queuing priority used during network congestion. Determines access to channels.

Virtual Network Id

Definition: identifies the Virtual Network that the service and feature profiles relate to. Within a single VN a MET may have one voice, data, fax and/or avd service type. Features and restrictions for those services are defined on the basis of the METs membership in that VN. If the MET required an additional instance of a service that it already subscribed to, (e.g. a second voice number), a second virtual network assignment would be required. Features and restrictions for that second membership can be defined with no relation to the existing VN membership, but all elements that relate to the MET level cannot change without a ripple effect to the other services.

VMS Instance Type

Definition: Part of the Event Message

Vocoder Id

Definition: Vocoder version currently installed in the MET. CMIS will only have the MET Class ID that a particular METs equipment maps to. NE/SE originates this and other data that describes the MET Class and sends it to the NOC.

Working Configuration

Definition: The set of resources currently being modified by the engineer. This may be an existing, complete configuration which the engineer is modifying, or may be a new, partial (or initially empty) configuration.

A Availability

AAC Airline Administrative Communications

AARM Access Authentication Request

ABH Average Busy Hour

AC Alternating Current

ACU Access Channel Unit

ACU Antenna Control Unit

AD Attribute Dictionary

AEDC After Effective Date of Contract

AFC Automatic Frequency Control

AFS Antenna/Front-end Subsystem

AGC Automatic Gain Control

AIOD Automatic Number Identification Outward Dialing

AMI Alternative Mark Inversion

AMPS North American Analog and Digital Cellular Networks

AMSC American Mobile Satellite Corporation

AMS(R)S Aeronautical Mobile Satellite (Route) Service

AMSS(R) Aeronautical Mobile Satellite Services (Reserved)

ANI Automatic Number Identification

ANSI American National Standards Institute

ANT Antenna

AOC Aircraft Operational Communications

APC Airline Passenger Communications

API Applications Program Interface

AR Automatic Roaming

ARC Atlantic Research Corporation

ASK Access Security Key

ASN.1 Abstract Syntax Notation One

AT Command set for a DTE to communicate with asynchronous host

ATC Air Traffic Control

AVD Alternate Voice/Data Calls

AWGN Additive White Gaussian Noise

AZ Azimuth

B8ZS Bipolar with 8 Zeros Substitution

BB Bulletin Board

BBS Bulletin Board Service

BER Bit Error Rate

BERT Bit Error Rate Tester

BID Beam Identifier Code

BIT Built In Test

BITE Built-In Test Equipment

BPS Bits Per Second

BS Base Station

BSPU Baseband Signaling Processing Unit

BSS Base Station Switch

C/No Carrier to Noise Power Density Ratio

CAC Channel Access and Control

CAF Call Failure Message

CCCS Command, Control, and Communications Subsystem

CCIR Consultative Committee International de Radio

CCITT Consultative Committee International Telegraph and Telephone

CCU Communications Channel Unit

CD Call Delivery

CDR Call Detail Record

CDR Critical Design Review

CDRL Contract Data Requirements List

CE Common Equipment

CG Control Group

CGID Control Group Identification Number

CGS Communications Ground Segment

CHA Channel Assignment Message

CHREL Channel Release Message

CHREQ Channel Request Message

CI Configuration Item

CIBER Cellular Intercarrier Billing Exchange Roamer

CIC Carrier Identification Code

CM Configuration Management

CMIP Common Management Information System

CMIS Configuration Management Information System

CMIS Customer Management Information System

COTS Commercial off-the-Shelf

CP Circuit Pool

CPD Call Processing Demonstration

CPS Circuit Pool Segment

CPU Central Processing Unit

C/PV Commissioning/Performance Verification

CRC Cyclic Redundancy Check

CS Communications System

CSC Computer Software Component

CSCI Computer Software Configuration item

CSDT Channel Switchover Detection Time

CSF Critical System Functionality

CSMA/CD Carrier Sense Multiple Access with Collision Detection

CSMP Circuit Switch Management Processor

CSMPCS Circuit Switch Management Data Processor Equipment Communications System

CSPU Channel Signal Processing Unit

CSR CAC Statistics Request

CSREP Call Status Reply Message

CSREQ Call Status Request Message

CSU Computer Software Unit

CSUG Computer Software Unit Group

CTB Customer Test Bed

CTN Cellular Telephone Network

CTN Cellular Terrestrial Network

CTNI Cellular Telephone Network Interface

CU Channel Unit

CUD Call User Data

CUG Closed User Group

CUP Channel Unit Pool

CUS Channel Unit Subsystem

CVR Cellular Visitor Registration

CVRACK Cellular Visitor Registration Acknowledge

CW Carrier Wave

CWCHA Call Waiting Channel Assignment Message

DAMA Demand Assignment Multiple Access

db Database

dbc Decibel Relative to Carrier

dB decibels

dBi dB Relative to Isotropic

dBm dB relative to 1 milli watt

dBW decibels relative to 1 watt

D bit `Data Configuration` bit in X.25

DBMS DataBase Management System

dBw dB Relative to 1 Watt

DC Direct Current

DCE Data Circuit Terminating Equipment

DCE Data Communications Equipment

DCL Digital Command Language

DCN Down CoNverter

DCR# Document Control Release #

DCU Data Channel Unit

DD Design Document

DDCMP Digital Data Communications Message Protocol

DDS Direct Digital Synthesis

DEC Digital Equipment Corporation

DECmcc Digital's Network Management System

DEQPSK Differential Encoded Quadrature Phase Shift Keying

DET Data Equipment Terminal

DFD Data Flow Diagram

DH Data Hub

DH-D Outbound Time Division Multiplex Channel from Data Hub to Mobile Terminal

DHP Data Hub Processor

DHSI DH-D Selector Identification Code

DID Direct inward Dialing

DlDs Data Item Descriptions

DME Dial-Up Modem Emulation

DMQ DEC Message Queue

DMS Digital Multiplex System

DN Directory Number

DNS Digital Name Service

DOC Canadian Department Of Communications

DOD Direct Outward Dialing

DPSK Differential Phase Shift Keying

DQPSK Differentially Encoded Quadrature Phase Shift Keying

DS0 Digital Service Level Zero (single 64K b/s channel)

DS 1 Digital Service Level One (twenty four voice channels)

DSP Digital Signal Processing

DSSS 1 Digital Subscriber Signaling System 1

DTC Digital Trunk Controller

DTE Data Terminal Equipment

DTE Data Terminal Element

DTMF Dual Tone Multiple Frequency

DVSI Digital Voice Systems, Inc.

Eb/No Bit Energy to Noise Power Density Ratio

ECN Engineering Change Notice

EFD EF Data, Inc.

EFTIN Encrypted Forward Terminal Identification Number

E-I Exchange-Interexchange

EIA Electronic industries Association

EICD Element Interface Control Document

EIE External Interface Equipment

EIRP Equivalent Isotropic Radiated Power

E1 Elevation

EMC ElectroMagnetic Compatibility

EMI ElectroMagnetic Interference

eng engineer or engineering

EO End Office

EO External Organizations

EOD End of Data

ESN Electronic Serial Number

FAX Facsimile

FCA Functional Configuration Audit

FCC Federal Communications Commission

FCS Fading Channel Simulator

FDMA Frequency Division Multiple Access

FEC Forward Error Correction

FES Feederlink Earth Station

FES-C Inbound Communication channel from Feederlink Earth Station to Mobile Terminal

FES-I Interstation signaling channel from Feederlink Earth Station to Group Controller

FES/MT Feederlink Earth Station/Mobile Terminal

FES-RE Feederlink Earth Station-Radio Frequency Equipment

FES-TE Feederlink Earth Station Terminal Equipment

FFT Fast Fourier Transform

FIS Feederlink Earth Station Interface Simulator

FIT Fault Isolation Tests

FIU Fax Interface Unit

FMT Fixed Mobile Terminal

FMA Field Programmable Gate Array

FPMH Failures per Million Hours

FRO Frequency Reference Oscillator

FT Fault Tolerant

FTE Fax Terminal Equipment

FTIN Forward Terminal Identification Number

G/T Gain to System Noise Ratio

GBF Gateway/Base Function

GBS Gateway Base System

GC Group Controller

GC-I Interstation signaling channel from Group Controller to Feederlink Earth Station

GC-S Time Division Multiplex Signaling channel from Group Controller to Mobile Terminal

GCSST GC-S Search Time

GEN Generator

GHz Giga (1,000,000,000) Hertz (cycles per second)

GMACS Graphical Monitor And Control System

GPIB General Purpose Instrument Bus

GPS Global Positioning System

GS Gateway Station

GSI GC-S Selector Identifier

GW Gateway

GWS Gateway Switch

GWS/BSS Gateway Switch/Base Station Switch

H/W Hardware

HCHREQ Handoff Channel Request

HDP Hardware Development Plan

HLR Home Location Register

HMI Human Machine interface

HOT Hand-off Test

HPA High Power Amplifier

HRS Hardware Requirements Specification

HWCI Hardware Configuration Item

HW/SW Hardware/Software

Hz Hertz

I In Phase channel

IAW In Accordance With

IC Interexchange Carrier

ICD Interface Control Document

ICI Instrument Control Interface

ICP Intelligent Cellular Peripheral

ICU Interstation Channel Unit

ICWG Interface Control Working Group/Interface Coordination Working Group

ID Identification

IEEE Institute of Electrical and Electronics Engineers

IF Intermediate Frequency

IFIS intermediate Frequency Subsystem

IFL Interfacility Link

IF IFL Intermediate Frequency Internal Facility Link

IHO Interstation Hand-Off

IICD Internal Interface Control Document

IICWG Internal Interface Control Working Group

IM Intermodulation

IMBE Improved Multiband Excitation

IOC Input/Output Controller

IP Internet Protocol

ISCU Interstation Signaling Channel Unit/Interstation Channel Unit

ISDN Integrated Services Digital Network

ISL Interstation Signaling Link

ISO International Standards Organization

IVDCPD Integrated Voice & Data Call Processing Demonstration

IVDM Integrated Voice/Data Mobile Terminal

KBPS Kilo (1,000) Bits per Second

kHz Kilohertz

KLNA K-band Low Noise Amplifier

KP Key Pulse

LAN Local Area Network

LAP Link Access Procedure

LAPB Link Access Procedure using a balanced mode of operation

LATA Local Access and Transport Area

LBP Local Blocking Probability

LCN Logical Channel Number

LLCSC Lower Level Computer Software Component

LLNA L-band Lowe Noise Amplifier

LLS Lower Level Specification

LNA Low Noise Amplifier

LOI Level of Integration

LPP Link Peripheral Processor

LRU Line Replaceable Unit

LRU Lowest Replaceable Unit

LSSGR Loyal Access and Transport Area Switching Systems Generic Requirements

MAP Maintenance Administrative Position

MAP Mobile Application Part

M bit `More Data` bit in X.25

M&C Monitor and Control

MCC Management Control Center

MCGID Mobile Data Service Control Group identification Number

MDLP Mobile Data Service Data Link Protocol

MDS Mobile Data Service

MDSR MDLP Statistics Request

MEA Failure Modes and Effects Analysis

MEF Minimum Essential Functionality

MELCO Mitsubishi Electronic Company

MET Mobile Earth Terminal (a.k.a. MT)

MET-C Communication Channel Between Mobile Terminal and Feederlink Earth Station

MET-DRd Inbound Slotted Aloha Data Channel

MET-DRr Inbound Slotted Aloha Reservation Channel

MET-DT Inbound Packet Time Division Multiple Access Channel

MET-SR Random Access Signaling Channel from Mobile Terminal to Group Controller

MET-ST Time Division Multiple Access signaling channel from Mobile Terminal to Group Controller

MF Multiple Frequency

MFID Manufacturer Identification

MGSP Mobile Terminal to Group Controller Signaling Protocol

MHz Mega Hertz (cycles per second)

MIB Management Information Base

MIR Management Information Region

MIRQ MT Initialization Request

MIS Mobile Terminal Interface Simulator

MIS Mobile Earth Terminal Interface Simulator

ML Message Layer

MLCSC Mid Level Computer Software Component

MLP Multilink Procedure

MMI Man Machine Interface

MMRS Mobile Road Service

MMSS Maritime Mobile Satellite Services

MNMS Mobile Data Service Network Management Subsystem

MNP Multi Network Protocol

MODEM MODulator/DEModulator

MOS Mean Opinion Score

MOV Method of Verification

MPLP Mobile Data Service Packet Layer Protocol

MPR MPR Teltech Inc.

MRI Minimum Request Interval

MRS Mobile Radio Service

MSAT Mobile Satellite

MSC Mobile Switching Center

MSS Mobile Satellite Service

MSSP Mobile Terminal Specialized Services Protocol

ms millisecond

MT Mobile Terminal

MT-C Communication Channel Between Mobile Terminal and Feederlink Earth Station

MT-DRd Inbound Slotted Aloha Data Channel

MT-DRr Inbound Slotted Aloha Reservation Channel

MT-DT Inbound Packet Time Division Multiple Access Channel

MT/NR Mobile Terminal/Net Radio

MT ASK Mobile Terminal Access Security Key

MTBF Mean-Time Between Failures

MTBRA Mean-Time Between Restoral Actions

MTCRS Mobile Telephone Cellular Roaming Service

MT-MET Mobile Terminal to Mobile Terminal

MT-MT Mobile Terminal to Mobile Terminal

MTP Mobile Data Service Transaction Protocol

MT-PSTN Mobile Terminal/Public Switched Telephone Network

MTS Mobile Telephone Service

MT-SR Random Access Signaling Channel from Mobile Terminal to Group Controller

MTSR MTP Statistics Request

MT-ST Time Division Multiple Access Signaling Channel from Mobile Terminal to Group Controller

MTTR Mean-Time to Repair

MTX Mobile Telephone Exchange

MULP Mobile Data Service Unacknowledged Link Protocol

MUSR MULP Statistics Request

NACN North American Cellular Network

NADP North American Dialing Plan

NANP North American Numbering Plan

NAP Network Access Processor

NAP-C Network Access Processor for the Communications Channel

NAP-CU Network Access Processor-Channel Unit

NAP-D Network Access Processor for the Data Channel

NAP-N Network Access Processor for the Network Radio Channel

NAP-S Network Access Processor for the Signaling Channel

NAS Network Access Subsystem

NASP National Aerospace Plan

NCC Network Communications Controller

NCC Network Control Center

NCC-RE Network Communications Controller Radio frequency Equipment

NCC-TE Network Communications Controller Terminal Equipment

NCS Network Control System

NCU Net Radio Control Unit

NCU Net Radio Channel Unit

NE Network Engineering

NEBS New Equipment Building System

NE/SE Network Engineering/System Engineering

NIM Network Module

NM Network Module

NMP Network Management Process

NMS Network Management System

NMS/CMIS Network Management System/Customer Management Information System

NOC Network Operations Center

NOC-FES Network Operations Center-Feederlink Earth Station

NPA Numbering Plan Area

NR Net Radio

NRCHA Net Radio Channel Assignment

NRCHREL Net Radio Channel Release

NRCHREQ Net Radio Channel Request

NRDVI Net Radio Dispatcher Voice Interface

NRS Net Radio Service

NRZ Non-Return to Zero

NT Northern Telecom

NTL Northern Telecom Limited

NTP Northern Telecom Practice

NVM Non-Volatile Memory

OA&M Operation, Administration, and Maintenance

O&M Operations and Maintenance

OJJ On the Job Training

OM Operational Measurements (from GWS)

OS Operating System

OSF Open Software Foundation

OSI Open Systems Interconnection

OSR Operational Support Review

PA Product Assurance

PAC Pre-emption Acknowledge Message

PAD Packet Assembler/Disassembler

PAP Product Assurance Plan

PBX Private Branch Exchange

PC Process Control

PCM Pulse Code Modulation

PC-RFMCP PC Based RFM Control Processor

PC-SCP PC Based Systems Control Processor

PCSTR Physical Channel Statistics Request

PCT Provisioning Criteria Table

PCU Pilot Control Unit

PCU Pilot Channel Unit

PDAMA Priority Demand Assignment Multiple Access

PDN Packet Data Network

PDR Preliminary Design Review

PDU Protocol Data Unit

PE Protocol Extension

PER Packet Error Rate

PERSP Packet Error Rate Sample Period

PERT Packet Error Rate Threshold

PIP Program Implementation Plan

PLP Packet Layer Protocol

PLT Pilot

PMR Project Management Review

PMT Pre-emption Message

PN Private Network

PN Pseudo Noise

PNIC Private Network Identification Code

PPM Pulses per Minute

PS Processor Subsystem

PSDN Private Switched Data Network

PSDN Public Switched Data Network

PSTN Public Switched Telephone Network

PTT Push-To-Talk

PVC Performance Virtual Circuit

PVT Permanent Verification Test/Performance Verification Test

Q Quadrature Phased Channel

QA Quality Assurance

Q bit `Qualified Data` bit in X.25

QPSK Quadrature Phase Shift Keying

RAM Random Access Memory

RAM Reliability, Availability, Maintainability

RDB Relational DataBase

REMS Remote Environmental Monitoring System

Req Requirement

Rev Revision

RF Radio Frequency

RFE Radio Frequency Equipment

RF IFL Radio Frequency Inter Facility Link

RFM Radio Frequency Monitor

RFP Request For Proposal

RFS Radio Frequency Subsystem

RHCP Right Hand Circularly Polarized

RMS Remote Monitoring Station

RMS Remote Monitor Subsystem

RNO Remote NOC Operator

ROM Read Only Memory

RR Receiver Ready

RS Requirements Specification

RS-232C Electronics Industry Standard for unbalanced data circuits

RSP Radio Standard Procedure

RTIN Reverse Terminal Identification Number

RTM Requirements Traceability Matrix

RTP Reliable Transaction Protocol

RTR Reliable Transaction Router

RTS Reliable Transaction Service

RTS Receiver/Tuner System

Rx receive

S/W Software

SCADA Supervisory Control and Data Acquisition

SCCP Signaline Connection Control Part

SCPC Single Channel Per Carrier

SCR Software Change Request

SCS System Common Software

SCU Signaling Channel Unit

SDD Software Design Description

SDID Seller Data Item Description

SDLC Synchronous Data Link Control

SDP Software Development Plan

SDPAP Software Development Product Assurance Plan

SDR System Design Review

SDRL Seller Data Requirements List

SE Systems Engineering

SEC Setup Complete Message

SEDP Software Engineering Development Plan

SEE Software Engineering Environment

SEEP Software Engineering Environment Plan

SID System Identifier Code

SIF System Integration Facility

SIT Special Information Tones

SLOC Source Lines of Code

SLSS Station Logic and Signaling Subsystem

SM Site Manager

SMAC Station Monitor Alarm and Control Subsystem

SMDS Satellite Mobile Data Service

SMP Software Management Plan

SMRS Satellite Mobile Radio Service

SMSC Satellite Mobile Switching Center

SMTS Satellite Mobile Telephone Service

SNA Systems Network Architecture

SNAC Satellite Network Access Controller

SNACS Satellite Network Access Controller Subsystem

SNMP Simple Network Management Protocol

SNR Signal to Noise Ratio

SOC Satellite Operation Center

SOW Statement of Work

SP Start Pulse

SPAP Software Product Assurance Plan

SPP Satellite Protocol Processor

SQL Software Query Language

SRR Systems Requirements Review

SRS Software Requirements Specification

SS7 Signaling System No. 7

SSA Sloppy Slotted Aloha

SSTS Satellite Transmission Systems, Inc.

STP Signal Transfer Point

STP System Test Program

STS System Test Station.

STSI Satellite Transmission Systems, Inc.

SU Signaling Unit

SUES Shared-Use Earth Station

SVC Switched Virtual Circuit

SVVP Software Verification and Validation Plan

SVVPR Software Verification and Validation Plan Review

S/W Software

›TI! Top Level Specification

T-1 Digital Transmission link, 1.544 Mega-bits per second

TCP/IP Transmission Control Protocol/Internet Protocol

TCAP Transactions Capabilities Application Part

TCF Training Check Frame

TD Transmission Demonstration

TDM Time Division Multiplex

TDMA Time Division Multiple Access

TDMSI Time Division Multiplex Selector ID

TE Terminal Equipment

Telecom Telephonic Communications

TDM Time Division Multiplex

TDMA TDM Access

TID Terminal Identification

TIM Timing

TIM Technical Interchange Meeting

TIN Terminal Identification Number

TIS Terrestrial Interface Subsystem

TLCSC Top Level Computer Software Component

TLS Top Level Specification

TMI Telesat Mobile incorporated

TMS Test and Monitor Station

TNI Terrestrial Network Interface

TPP Test Plan and Procedure

TT&C Telemetry, Tracking and Control

Tx Transmit

UCN Up CoNverter

UDS Unacknowledged Data Delivery Service

UIS User Interface Subsystem

UPC Uplink Power Control

UTR Universal Tone Receiver

UW Unique Words

V&V Verification and Validation

VAC Value-Added Carrier

VAX Model Identification of a Digital Equipment Corporation system

VAX Virtual Address extension (proprietary name used by DEC for some of its computer systems)

VCN Virtual Circuit Number

VF Voice Frequency

VLR Visitor Location Register

VN Virtual Network

VPN Virtual Private Network

VUP VAX Unit of Processing

V.22bis Modem Standard for 24()0 Baud Service Over Telephone Lines

V.25 Procedure for setting up a data connection on the Public Switched Telephone Network

V.26, V.28 Electrical specification of interchange circuits at both the Data Terminal Equipment and Data Communications Equipment sides of the interface (similar to RS-232-C)

V.32 High Speed Serial Link, Physical Layer Definition

V.35 X.25 physical layer interface used to access wideband channels (at data rates up to 64 kbit/s)

WAN Wide Area Network

XCR X.25 Configuration Request

XICD External Interface Control Document

XICWG External Interface Control Working Group

X.3 Specification for facilities provided by the Packet Assembler/Disassembler

X.21 X.25 physical layer interface for Data Terminal Equipment and Data Communications Equipment using synchronous transmission facilities

X.21b is X.25 physical layer interface for Data Terminal Equipment designed for interfacing to synchronous V-series modems to access data networks

X.25 Specification for interface between Data Terminal Equipment and Data Communications Equipment for terminals operating in packet mode

X.28 Specification for interaction between loval terminal and Packet Assembler/Disassembler

X.29 Specification for interaction between Packet Assembler/Disassembler and remote packet mode terminal