Communications Protocol for Switching Systems

This application is related to the following U.S. Patent Applications:

Application Ser. No. 08/020,031 entitled "Language Independent Self-Centering Menu Handling of Traffic Recording Presentation" and application Ser. No. 08/107,337 entitled "Monitor Screen Graphic Value Indicator System". This application is also related to U.S. Pat. No. 5,163,055 entitled "Communication System Using a Fault Tolerant Protocol" and U.S. Pat. No. 5,181,204 entitled "Method and Apparatus for Error Tracking in a Multitasking Environment".

All cross referenced applications have been filed on even date herewith and assigned to the assignee of the present invention. All of these ralated applications are hereby incorporated herein by reference.

1. Field of the Invention

The present invention relates to interfaces within communications systems and, more particularly, to a protocol that may be used between a private automatic branch exchange (a "PABX") and voice and data terminals connected to the PABX.

2. Description of Related Art:

Voice and data switching systems typically comprise a central system and end point devices connected to the central system via extension lines. The end point may be either analog devices or digital devices. Examples of analog end point devices are modems and rotary (or tone based) telephone sets. Examples of digital end point devices are terminal adaptor units ("TAU's", which are also referred to as data circuit equipment or "DCE") and digital telephones.

In general, analog devices communicate with the central system via manipulations of the electrical interface characteristics of the extension line. With such a communication scheme, features and functions are generally restricted to those that are available within the central system and which can be reached by such a limited signalling capability. Digital devices, on the other hand, which are usually restricted to a given PABX, typically incorporate advanced signalling channels over the extension line interface. These advanced signalling channels can operate to increase the communication level between the end point devices and the system.

Digital lines now supported by a number of PABX's are examples of the aforementioned extension lines. These digital lines can allow better control of transmission parameters to and from digital telephones. Further, these digital lines are capable of allowing implementations of more sophisticated protocols than those presently used. In addition, as the interfaces between the TAU's and the system, and between the TAU's and the terminals, are constantly evolving the family of TAU's is rapidly expanding. This is potentially advantageous as the more sophisticated the protocol used to communicate between systems and, e.g. , digital telephones, the more sophisticated the features that can be implemented into the digital telephones or other such voice and/or data terminals.

The protocol used on a digital extension between a PABX and its associated feature phones and TAU's is always unique to each PABX manufacturer because feature phones and data interfaces are always custom designed and proprietary. Because price comparisons among PBX's are typically done based upon cost per line, heretofore it has been common to minimize cost of feature phones and TAU's by providing them with only simple features and by using simple protocols to communicate their activities to the central software corresponding to the state of the device known by the central software.

Became development heretofore has progressed based upon the simple feature/simple protocol philosophy discussed above, presently, each time a new data device is introduced with new features, new state tables need to be introduced in the call processing software. Because compatibility with all previous devices is also generally maintained, call processing software has been growing and continues to grow larger and larger. Each feature addition or improvement involves a change in both the terminal adaptor firmware and in the state tables in the call processing software. Needless to say, the above methods for dealing with changes are inefficient and have become ungainly. It is a shortcoming and deficiency of the prior art that a better method for dealing with improved TAU's has not been developed.

Although no prior art materials which either disclose or suggest the protocol disclosed and claimed herein are known, there are a number of prior art references which bear some relation to the subject matter of the present invention. These references are U.S. Pat. Nos. 4,530,051 and 4,256,926. Each of these references is discussed briefly below.

U.S. Pat. No. 4,530,051 to Johnson et al. is directed to a method and apparatus for executing parts of a program process on two processors of a multiprocessor system. Johnson et al. describe a complex messaging system where intraprocess messages need to be sent among different processors.

U.S. Pat. No. 4,256,926 to Pitroda et al. is directed to a microprocessor control complex for a telecommunication switching system. Pitroda et al. describe a then-new Wescom PABX and its protocol between the attendant console and the PABX.

Review of the above-described references reveals no teachings of a solution such as that presented herein to the inefficiencies, shortcomings and deficiencies of the prior art discussed above.

The present invention overcomes the shortcomings and deficiencies of the prior art by providing a switching system protocol including a plurality of signals that may be transmitted from an end point device to a central system and a plurality of signals that may be transmitted from the central system to the end point device. The various signals relate to device and system functions, parameters and states.

The present invention provides a grouping of high level messages which are function oriented and not device specific. Using such messages, in systems practicing the protocol of the present invention the number of state tables in the call processing software are reduced and smarter terminal adapters which can process their own low level state tables may be accommodated.

Accordingly, it is an object of the present invention to provide a protocol that allows early introduction of additional features as well as new data devices in certain communication systems.

Another object of the present invention is to provide a protocol that increases system real-time processing capacity due to decentralization of the low level processing load.

Yet another object of the present invention is to provide a protocol that obviates the need for a change in call processing software and/or terminal adapter firmware each time a feature in a system is enhanced or optimized.

Still yet another object of the present invention is to provide a protocol that allows implementation of more flexible maintenance and fault recovery within certain systems because terminal adapters within such system take care of low level tasks.

A further object of the present invention is to facilitate and enhance communication by automated devices became such devices can be easily interfaced to terminal adapters for unattended automatic functions and for taking advantage of the local processing power.

For a more complete understanding of the present invention, and for further objects and advantages thereof, reference may now be had to the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram of a conventional switching system including line interface modules;

FIG. 2 is a block diagram of a line interface module such as those shown in FIG. 1;

FIG. 3 depicts certain data communications aspects of the system of FIG. 1;

FIG. 4 is a block diagram of an equipment function request signal according to the teachings of the present invention;

FIG. 5 is a block diagram of an equipment data message signal according to the teachings of the present invention;

FIG. 6 is a block diagram of an equipment function activate signal according to the teachings of the present invention;

FIG. 7 is a block diagram of an equipment data request signal according to the teachings of the present invention; and

FIG. 8 is a block diagram of a call status indication signal according to the teachings of the present invention.

Although the present invention is hereinafter described with reference to a particular environment and application, those skilled in the art will recognize and appreciate that the protocol of the present invention has wide applicability to situations in which two intelligent devices are interconnected for communication, data transfer and similar purposes. The specific embodiment described below thus merely constitutes one embodiment of the present invention, which embodiment has actually been implemented and found to work extremely well.

With the above understanding, referring now to FIG. 1, shown therein is a block diagram of portions of a certain communications system 10, designated the MD110 Intelligent Network, manufactured by the assignee of the present invention. At the heart of this system 10 is one or more line interface modules 12 (or "LIMs"), five of which are shown in the system depicted in FIG. 1. The various LIMs are interconnected by a group switch 14 using links 16 carrying a standard PCM format.

System 10 software is divided into central and regional operating segments. Each LIM contains all of the necessary regional software to ensure complete control of call processing within the LIM (intra-LIM communications ). Inter-LIM communications are controlled by central software, which is accessed as required by a LIM originating call processing to another LIM. Central software is duplicated in multiple LIMs for added reliability.

Referring now to FIG. 2, further details regarding LIMs are set forth in the form of a typical LIM block diagram. Each LIM consists of five hardware subsystems: (1) a line signalling subsystem containing interface circuit 18 (connecting the LIM with voice/data devices) and the service circuits for call processing functions; (2) a switching system 20 to permit two-way communication between the station trunks, and other equipment; (3) a processor subsystem 22 to direct all functions of the LIM processor; (4) an input/output subsystem 24 to provide a man-machine interface for system administration and maintenance; and a service/maintenance subsystem 26 to monitor system hardware and software, detect faults, generate alarms, and aid in fault clearing. Also shown in FIG. 2 are a multitude of various peripheral devices that can be connected to LIMs. These peripheral devices may be seen in FIG. 2 to include analog telephones 28, digital telephones (e.g., telephone 30), TAUs (e.g., TAU 32), as well as a number of other devices.

Referring now to FIG. 3, shown therein is a block diagram depicting data communication aspects of system 10. Internally, the system 10 may be seen to make no distinction between data and voice transmissions. Voice and data communications are performed independently or simultaneously using only a single twisted pair of wires. Data devices and digital telephone sets utilize the same digital line card. Data communications capability can be added or relocated using TAUs, e.g., the TAU models TAU 2520 34, TAU-S 36, and TAU-D 38, all manufactured by the assignee of the present invention, shown in FIG. 3.

Typical conventional TAUs, like models TAU-S and TAU-D manufactured by the assignee of the present invention, allow both asynchronous and synchronous operation. In an environment involving a system such as system 10, digital-to-analog or analog-to-digital conversion is not necessary for internal data switching. All TAUs operate in either full or half duplex modes. Typical TAUs have the flexibility to enable appropriate signals on the RS-232-C interface on data terminal equipment with various control requirements. In addition, conventional TAUs provide the proper characteristics such as speed, number of start/stop bits, interface type, and modes of transmission.

As mentioned in the description of related art section above, stimulus-response signaling is presently the standard method for propagating signals in switching system environments.

As also mentioned in the description of related art section above, such signalling has a number of shortcomings and deficiencies, which shortcomings and deficiencies are accentuated by certain relatively recent developments. For example, TAUs with increasingly sophisticated features, such as keyboard dialing and directories, are now being developed. Heretofore, to deal with these features more states have been added to the central software. This can and has required in some cases updates to the firmware of old devices so that they remain compatible with new software releases. Also, this method of handling increasingly sophisticated TAU residence features has required increasingly large amounts of real time.

In order to manage the increased complexity of TAUs and to keep the compatibility of old devices with an everchanging central software, the inventors of the present invention decided several fundamental technical changes were appropriate. First, it was recognized that distribution of some system intelligence, e.g., manipulatable or otherwise usable data stored in a memory, at the device level would be desirable. Such distribution could allow such a device (e.g., TAU 36 in FIG. 3) to locally process its own state table or sub-states of the main table in the control element 22 of the appropriate LIM 12 (see FIG. 2). Such a state table could be stored in a memory subcomponent (designated by reference numeral 37 in FIG. 3) of TAU 36. In making such a distribution, trade-offs in separating main-states from sub-states were deemed prudently made, recognizing that main-states should be stable, that is, not updated at each software release. Second, a higher level of communication protocol, comprising state-oriented signals, was developed.

The present invention effectively glows end point devices to track states simultaneously with central software. Having such state data readily available within a TAU (e.g., in the memory 37 of TAU 36) allows system intelligence also, i.e., means for acting upon the state information, to also be stored in the TAU. Advantages of such a distribution are numerous.

As should occur to those persons skilled in the relevant art upon reading this document, the distribution of the state tables and the functionally oriented signalling taught herein allow both state-machine control of TAUs, increased functionality, and more flexibility in the design of both TAUs and central software. Noteworthy advantages of state-machine control include isolation from digital telephone sets, more independent development evolution from the central software, and better fault recovery because the state machine is better defined and the messages are state oriented. Noteworthy advantages of increased functionality include end-to-end compatibility (equipment configuration per call basis, class of service functionality restriction, accommodation of a larger range of data devices and improved maintenance functions).

By way of example only, set forth below is a technical description of one possible embodiment of the present invention. This example should be of significant utility for those skilled in the art to understand and appreciate the structure and operation taught herein. It may be helpful to read this description while referring to FIGS. 4, 5, 6, 7 and 8, wherein the various signals are schematically shown.

Implementation Description

The signals described in the following sections of this document are intended to cover a broad range of applications and contain features/functions which are not fully supported in present day switching systems. The intention is to provide an open-ended signal design which can be expanded as new features are supported without affecting already designed devices.

In the following descriptions, the signals are defined with parameters for all possible feature/function applications.

Equipment Function Request

The Equipment Function Request signal is multipurpose signal with a unique signal number followed by a number of parameters. Each parameter has a specific meaning and is located in a fixed position within the signal.

Equipment Data Message

The Equipment Data Message signal is used to inform the system of changes in the local data parameters with respect to the RS-232 interface (Note: of course, any number of interfaces can also be used with the protocol of the present invention, such interfaces specifically including RS-422 and X 21 interfaces). This signal is sent whenever a change in the RS-232 interface parameters is detected by the device (typically as a result of local autobaud/format detection). 1 This signal is also sent in response to an Equipment Data Request (EQUDATREQ).

Equipment Function Activate

The Equipment Function Activate signal is used by the system to activate/deactivate local functions in the device such as key board dialing, menu interfaces, TX/RX data speeds and formats, etc.

Equipment Data Request

The Equipment Data Request signal is used by the system to request the current RS-232 interface parameters, data format and speed.

Call Status Indication

The Equipment State Update is used by the system to inform the device of a change in state. More specifically it is used to transfer call progress information such as the CP codes now displayed on existing data equipment.

Referring now to FIGS. 4, 5, 6, 7 and 8, the five signals described above may be schematically seen. Specifically, the above-described equipment function request signal is depicted in FIG. 4, the equipment data message signal is depicted in FIG. 5, the equipment function activate signal is depicted in FIG. 6, the equipment data request signal is depicted in FIG. 7, and the call status indication signal is depicted in FIG. 8. It may be noted that all five signals include portions 40 identifying the number of bytes in the signal, identity of the relevant device and signal number. Additionally, each signal contains a checksum portion 42, that is, a redundant check in which groups of digits may be summed without regard for overflow, which sum may then be checked against a previously computed sum to verify accuracy. Finally, each signal except that shown in FIG. 7 contains a unique, operative portion 44 which gives the signal its individual functionality as described above.

It should now be fully appreciated by those skilled in the art that the present invention provides a new and useful protocol comprising signals that are function oriented. Using the protocol of the present invention, in systems such as system 10 described herein the number of state tables in the call processing software can be reduced and smarter TAUs accommodated. The present invention facilitates system improvement and performance. Also, the protocol of the present invention allows implementation of a more flexible maintenance and fault recovery because terminal adapters can take care of low level tasks. Still further, the protocol of the present invention facilitates and enhances communication by automated devices became such devices can be easily interfaced to terminal adapters for unattended automatic functions and for taking advantage of local processing power.

Obviously, numerous modifications and variations are possible in view of the above teachings. Accordingly, within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein.