Transmitting messages across telephony protocols

[0001] This application claims the benefit of the priority of U.S. Provisional Application Ser. No. 60/626,775, entitled “System and Method for Integrating Enterprise and Cellular Telecommunications Services,” filed Nov. 10, 2004 and of U.S. patent application Ser. No. ______, entitled “Seamless Transitions of Active Call between Enterprise Telecommunications Networks and Licensed Public Telecommunications Networks” filed Jan. 5, 2004.

[0002] The present description relates generally to integrating enterprise telephony systems with public telephony systems. More particularly, this description relates to signaling between a subscriber terminal of a licensed wireless system, for example a public cellular telephone system, and a switching center of a private enterprise system, such as an enterprise voice over IP wireless exchange.

[0003] Licensed wireless telecommunications systems provide mobile wireless communications to users mobile transceivers. Licensed wireless systems may be public cellular telephone systems, Personal Communication Services (PCS) telephone systems, or other types of mobile telecommunications systems. Wireless transceivers may include cellular telephones, PCS telephones, wireless-enabled personal digital assistants, wireless modems, etc.

[0004] Licensed wireless systems use wireless signal frequencies that are licensed from governments, quasi-governmental agencies, or other official licensing agencies. Large fees may be paid for access to these frequencies or there may be complex application procedures making the frequency resources expensive and scarce. In a cellular telephone and data system, expensive base station equipment is used to support communications on licensed frequencies. So the number of base stations and the amount of frequency bandwidth allocated to each use is limited by the cost of obtaining frequencies and installing transceivers. As a result, the quality of service (voice quality and speed of data transfer) in licensed wireless systems may be considerably less than the quality of service provided by landline (wired) connections.

[0005] Landline (wired) connections are extensively deployed and generally perform at a lower cost with higher quality voice and higher speed data services. The problem with landline connections is that they constrain the mobility of a user. Traditionally, a physical connection to the landline is required. Enterprises may implement a landline telecommunications system with a telephone switch, such as a PBX (Private Branch Exchange) and a number of wired subscriber units, such as desk telephones. An IP (Internet Protocol) PBX may integrate the telephone network with a data network and communicate voice and data over one wired network. Additional switches may be used for additional user terminals or to connect with additional sites.

[0006] Unlicensed frequencies may be used to provide mobility to wired users in the landline network. Unlicensed radios are typically low power and short range to avoid interference with neighboring unlicensed radios. The lack of licensing costs and the low power of the radios greatly reduce the cost as compared to, for example a cellular telephone system. Due to the large amount of frequency spectrum available in unlicensed systems and the low power of the radios, common unlicensed telecommunications systems offer higher quality of service than, for example, cellular telephone or data modem service. Most current systems, such as WiFi, WLAN (wireless local area network), Bluetooth PAN (Personal Area Networks), and IEEE (Institute of Electrical and Electronics Engineers) 802.11 systems, provide a modest range from a base station and do not support fast moving mobile stations. Wireless LANs are used with an IP PBX to communicate telephone voice signals over the wireless data network through wireless IP telephones.

[0007] In order to use high quality low cost unlicensed telecommunications when possible and high cost, high mobility, low quality, licensed telecommunication when necessary, a user may use a mobile station that is capable of operating in both the licensed and unlicensed wireless domain. If a user has an active call that is communicating through the licensed domain, however, the unlicensed switching system may not be able to signal the subscriber terminal. This may prevent the user from enjoying features of the unlicensed system. If the call originated in the unlicensed system and was transferred to the licensed system, the licensed system may prevent important call control signaling from being sent between the unlicensed switching system and the subscriber station.

[0008] Call control and related messaging may be communicated between systems that operate using different protocols. In one version, a process is described that includes generating a message in a first telephony signaling protocol, wrapping the message in a message of a second telephony signaling protocol, and sending the wrapped message to a telephony switch using the second telephony signaling protocol.

[0009] The invention may be more fully appreciated in connection with the following detailed description taken in conjunction with the accompanying drawings, in which like reference numerals refer to corresponding parts throughout the several views of the drawings, and in which:

[0010] FIG. 1 is a block diagram of an enterprise communications network coupled to a cellular communications network according to an embodiment of the present invention;

[0011] FIG. 2 is a block diagram of a user terminal according to an embodiment of the present invention;

[0012] FIG. 3 is a block diagram of an interworking facility according to an embodiment of the present invention;

[0013] FIG. 4 is a flow diagram of handing over an active call from an unlicensed wireless system to a licensed wireless system from the perspective of an interworking facility according to an embodiment of the present invention;

[0014] FIG. 5 is a flow diagram of handing over an active call from an unlicensed wireless system to a licensed wireless system from the perspective of a mobile station according to an embodiment of the present invention;

[0015] FIG. 6 is a diagram of messages for handover from an enterprise system to a licensed communications system according to an embodiment of the present invention;

[0016] FIG. 7 is a diagram of messages for handover from a licensed communications system to an enterprise system according to an embodiment of the present invention;

[0017] FIG. 8 is a diagram of messages for signaling between a licensed communications system and an enterprise system according to an embodiment of the present invention; and

[0018] FIG. 9 is a flow diagram of communicating encapsulated messages according to an embodiment of the present invention.

[0019] An unlicensed wireless enterprise communication system may be seamlessly connected to a licensed wireless system, so that a user may move from one system to the other without interruption. The unlicensed wireless system may be a short-range wireless voice or data system or both that covers an office, an office suite, a building or a campus using a wireless network and a switch to establish circuit switched or packet switched connections between subscribers on the network and with external devices. The external connection may be to the PSTN (Public Switched Telephone Network), the Internet, a WAN (Wide Area Network) or any other external connection.

[0020] A mobile station for the unlicensed wireless system may be, for example, a wireless telephone, a smart phone, a personal digital assistant, or mobile computer with a built-in or attached radio or wireless NIC. The mobile station may also support a fixed wireless device that resembles a conventional desk phone or cordless base station.

[0021] FIG. 1 shows a simplified block diagram of unlicensed and licensed telecommunications systems in proximity to each other. On the left side of the diagram is an enterprise system 111 and on the right side of the diagram is a licensed wireless system such as a cellular telephone network 113. In between the enterprise domain and the cellular domain is a transitional domain 115 in which a user may have access to both networks. The PSTN (Public Switched Telephone Network) 117 and the Internet 119 are also shown as between the two domains. Both systems may be coupled to the PSTN, to the Internet or to both to allow voice and data user to communicate outside their respective networks.

[0022] The three domains of FIG. 1 are conceptual signaling and traffic domains and do not necessarily correspond to physical space. A radio located in any one domain may be able to receive transmissions from either the enterprise domain or the public domain. In some implementations, the enterprise domain may have a radio system sufficient to cover a building and its parking lot, while the public domain may also cover the same building and parking lot. In such a case, the radio coverage overlaps completely. It is not necessary to the invention that the radio coverage overlap nor that it be separate.

[0023] In the example of FIG. 1, the enterprise telecommunications system 111 has an IP PBX 121 and a WLAN (Wireless Local Area Network) AP (Access Point) coupled together through an enterprise network 125. The enterprise network may be a data network, a voice network or both. The IP PBX may be used to establish circuit switched connections, packet switched connections or both among subscribers on the network. In one embodiment, the enterprise network is a data packet network, such as a CSMA/CD (Carrier Sense Multiple Access with Collision Detection) network, such as Ethernet. The IP PBX uses the data network to establish packet switched voice connections that carry voice traffic over the network in a VoIP (Voice over Internet Protocol) format.

[0024] MSs (Mobile Station) 127, 129, 131 may communicate with the WLAN AP through radio, voice, or data channels. The MSs may take any of a variety of different forms suitable for the intended application. Some possible forms include a cellular telephone, a cordless telephone, a personal digital assistant and a portable computer with a radio interface. The enterprise network may support all of these forms and more in order to meet the needs of different subscribers in the enterprise. The enterprise network may also support FS (Fixed Station) terminals 133, 135. The fixed stations may be in the form of a desktop telephone, a desktop computer terminal or a control center.

[0025] The radio channel may also take a variety of different forms. In the example of FIG. 1, the radio channels are those typical for WLAN applications, most commonly a version of IEEE 802.11, such as 802.11g, often referred to as WiFi, or a variation on such a standard such as AirPort Extreme. Other wireless data or voice network channels may be used instead such as Bluetooth PAN (Personal Area Network), a PCS (Personal Communication System) standard or any other wireless voice or radio network. The particular choice of radio channel is not essential to the present invention.

[0026] Through the IP PBX, any one of the stations, fixed or mobile, may request a connection to any one or more other stations. So for example, a FS 133 user may dial a three-digit extension corresponding to a MS 127 user. The FS sends the three digit extension as a connection request to the IP PBX which polls the intended MS. The user at the intended MS may hear a ringing tone and can respond by picking up a handset or pushing a talk or answer button. If the user at the intended MS indicates that the user or the MS is available, then the IP PBX establishes a connection and the two terminals communicate through the enterprise network, with or without further involvement by the IP PBX.

[0027] The right side of FIG. 1 shows a simplified block diagram of a licensed wireless public telecommunications system, such as a cellular telephone network. The licensed wireless telecommunications system may take any of a variety of different forms. In the example of FIG. 1, a MSC (Mobile Switching Center) 141 is coupled through a cellular network 143 to a BSS (Base Station Subsystem) 145. Typically there will be several MSCs in the cellular network and several BSSs for each MSC. Each BSS may include a BSC (Base Station Controller) coupled to several BTSs (Base Transceiver Station). The cellular network may be a national, international, or local.

[0028] The particular design of the network will depend upon many different factors and in many situations there will be several different licensed wireless public telecommunications systems that overlap in the same area. These system may use different and incompatible wireless interfaces. In many metropolitan areas of the United States, there may be a dual-mode AMPS/DAMPS (Advanced Mobile Phone System/Digital AMPS), network, a GSM (Global System for Mobile Communications) network, including GPRS (GSM Packet Radio Service), a PCS (Personal Communication System) network, and a CDMA/UMTS (Code Division Multiple Access/Universal Mobile Telephone Service) network all covering the same physical area. Different carriers may operate on the same interface and other interfaces may be introduced as they are developed. In other locations, other interfaces may alternatively be used, such as PHS (Personal Handyphone System) or other public and proprietary interfaces. Any one or more of these system may be used with the present invention.

[0029] Between the Enterprise network 125 and the cellular network 143, FIG. 1 shows an interworking function (IWF) 147. The interworking function may be located with the enterprise domain 111, for example, it may be collocated with or be a part of the IP PBX, a router or other network device. It may also be an independent device on the enterprise network. Alternatively, the IWF may be integrated into the cellular network at the MSC, at a BSS or as a separate device. The IWF is shown as coupled directly to the enterprise network 125 and the cellular network 143, however other connections are also possible. For example, the IWF may connect to the enterprise domain 111 or the public wireless domain 113 or both through the Internet 119 or even through the PSTN 117.

[0030] A MS may be able to wander away from the enterprise domain 111. FIG. 1 provides an example of a MS 131 with a radio 153 for the enterprise domain WLAN AP and another radio 151 for the public wireless domain 113. Such a MS may be able to wander freely between all three domains and still have access to communications through the appropriate radio. Embodiments of the present invention may be used to allow the user to wander between the different domains and maintain an active call with no apparent interruption in service. The different domains appear to be seamless as the active call is handed off from one system to the other and back again as the user moves between the three domains.

[0031] FIG. 2 shows an example of a MS 131 that may be used according to some embodiments of the present invention. The MS of FIG. 2 may be in a form that resembles a dual mode cellular telephone, a cordless telephone, a PDA, a portable computer or a communications card in a larger computer. The functions of the MS are managed by a controller 213 that is coupled to a display 215, a user input device 217, a microphone 219 and a speaker 221. While these components are shown as incorporated into the MS, as may be done for example in a dual mode portable telephone, one or more of the components may be external. The microphone and speaker may be in an external wired or wireless headset or handset, the input device may be an external pointing device or keyboard, and the display may be a standalone monitor. External components may be wired to the device or wirelessly attached, as with a WLAN or Bluetooth radio connection. Any one or more of the illustrated user interface components may be removed for particular applications.

[0032] The controller may also be coupled to one or more other I/O (Input/Output) devices 223. These may be a synchronization port, an accessory port, a wired network interface, a docking port, a port replicator that permits further external devices to be attached or an interface to a base station. If the MS is adapted for use as a component of a larger computer system, then the display, input, microphone or speaker may be removed in favor of a bus interface 223. The bus interface may be a PC cardbus, PCI (Peripheral Component Interconnect) bus, a USB (Universal Serial Bus), IDE (Integrated Device Electronics), ATA (Advanced Technology Attachment) or other type of bus. The bus interface may be combined with a display 215, such as status LEDs (Light Emitting Diodes) and a speaker 221.

[0033] The controller 213 is further coupled to one or more storage devices 225 such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, a disk drive and an optical drive. The storage may be used to store operating instructions, applications, and data that is communicated with the enterprise and public domains. The controller is also coupled to a host DSP (Digital Signal Processor). The host DSP communicates data with the controller that is to be carried by the radios. The data may represent voice, text, graphics, applications, etc. The host DSP 227 controls the flow of the data to and from the radio and controls the radios themselves through an RF controller 229. The RF controller controls timing, frequencies, and other aspects of the radios.

[0034] The MS of FIG. 2 shows two radio paths from a single antenna 233. More radio paths may be used and, if the radio systems are sufficiently similar, then different radio interfaces may be carried by a single path. The antenna is coupled to a duplexer 231 controlled by the RF controller that routes signals from the appropriate system to the appropriate radio. The duplexer may be a passive frequency multiplexer and demultiplexer or it may be an active device. The duplexer is coupled to an enterprise radio 237 capable of communicating in the enterprise domain 111 and to a licensed band radio 241 capable of communicating in the public domain 113.

[0035] The radios 237, 241, controlled by the RF controller, may contain amplifiers, frequency converters, multiplexers, demultiplexers, equalizers, analog and digital converters, encoders and decoders, splitters and combiners, spreaders, despreaders and other elements. The radios are each coupled to voice and data codecs 235, 239 which are, in turn, coupled to the host DSP. Data or voice received from the antenna propagates through the duplexer to the appropriate radio, through the codec, to the host DSP and then to the controller for display, output, play or storage. Data or voice to be transmitted follows the opposite path from the controller through the DSP to the appropriate codecs and radio, through the duplexer and the antenna. The particular type of radio and transmission and reception chain may be adapted to suit different applications. More or less components than those shown in FIG. 2 may be used in a MS. The transmit and receive chains may be combined, as shown or separated.

[0036] FIG. 3 shows an example of an IWF 147 that may be used according to an embodiment of the invention to seamlessly interconnect a private enterprise telephony system 111 with a licensed public wireless telephony system 113. The IWF has a controller 313 that is coupled to one or more storage devices 315 such as RAM, ROM, flash memory, and disk drives, and to one or more I/O devices 317, such as user interface devices or remote administration and management interfaces. The storage may contain operating and application instructions for the controller as well as data to be communicated by the device.

[0037] A private interface 321 is coupled to one or more enterprise systems, such as an IP PBX 121. The interface may be coupled through a dedicated private line, a LAN, a WAN (Wide Area Network), the Internet or through any of a variety of other means. The private interface includes a signaling interface 323 to communicate signaling with the PBX and the user stations, such as handover requests, channel assignments and resource allocations and de-allocation. The signaling interface is coupled through a signaling line 324 which may be a shared connection, such as an IP interface through the Internet or it may be a dedicated connection, such as a private line or a backplane channel.

[0038] The private interface also includes a media interface 325 to send and receive traffic with user stations of the enterprise network over a media line 326. The media line may be shared with the signaling line or it may be a separate line. The traffic, as mentioned above, may be voice, text, data ,graphics, applications, instructions and more. In one embodiment, the private interface couples to the enterprise network and, using networking protocols, routes signaling and traffic to the appropriate device, such as the IP PBX or an MS.

[0039] Similarly, a public interface 327 is coupled to one or more public communications systems 113. The public interface has a signaling interface 329 for sending signaling over a signaling line 330 to the public system. In one embodiment, the signaling interface converts all signals to the SS7 (Signaling System 7) protocol and transmits them to an SS7 network of the public system. SS7 is used by many licensed public telephony systems. In another embodiment, the signaling interface adapts all signals to a unique protocol used by the particular public telephony system.

[0040] The public interface also includes a media interface 331 to carry traffic between the IWF and the public system over a traffic line 332. The public interface may be coupled to TDM (Time Division Multiplexed) trunks, such as T1 lines or any other type of traffic line, depending on the nature of the public system.

[0041] Using the two interfaces for each system, the IWF can communicate with each system using protocols and formats that are native to each system. As a result it may not be necessary to perform any modifications to either the enterprise domain or the public domain. A media converter 319 converts traffic between the two formats. Traffic received on the public interface is reformatted for transmission to the private domain through the private interface. Similarly traffic received on the private media interface is converted for transmission to the public domain. Alternatively, these conversions may be performed in the respective interface. Signaling may also be converted by the controller, the interfaces, or a signaling converter (not shown).

[0042] FIG. 4 shows an example of a how an interworking function may handle a seamless handover of a MS from the enterprise system 111 to the public wireless system 113 according to one embodiment of the invention. As shown in FIG. 4, the IWF first receives a handover request from a MS at block 410. In the example of FIG. 4, it may be assumed that the MS is in an active call on the enterprise network. The handover request is a request to hand the active call over from the enterprise network to the public network. Such a handover request may occur when, for example, the user is moving from the enterprise domain 111 to the transitional domain 115 and toward the public domain 113. The MS detects this as the signal for the enterprise domain active call grows weaker and signals from the public network, such as cellular BCH (Broadcast Channel) signals grow stronger. The handover request may be received by the IWF at its private signaling interface through the IP PBX and include information typically required by the public network. This information may include various identification and registration codes, RSSI (Received Signal Strength Indication) measurements made from various public network BCHs and other information.

[0043] Upon receiving the handover request, the IWF may establish a wireless channel between the PBX and the MS though a cellular BS (base station) at block 420. The BS is the one that the MS will be handed over to. This connection allow the active call to continue through the PBX to other party on the line through the BS to which the MS will be assigned. The connection may be made in several steps. For example, the IWF may first open a connection using its public signaling interface to a switching center, such as an MSC, of the public network at block 421. The IWF may also open a connection to the IP PBX at block 423 using its private signaling interface. Then the IWF may bridge the two connections at block 425.

[0044] With the connections established, the IWF may transfer the active call to the established wireless channel at block 430. This may by done by sending a handover request to the MSC at block 431 through its public signaling interface. The IWF may then receive a handover command in reply from the MSC at block 433 on its public signaling interface. The handover command will typically indicate the BS to which the MS is to be handed over, the traffic channel to be used and other administrative information. The IWF, using its private signaling interface may forward the handover command to the MS through the PBX at block 435. The MS after it acts on the command sends a message to the public system and the IWF may then receive a message from the MSC that handover is complete at block 437. After the call is successfully transferred, the IWF may then close the connection between the PBX and the MS at block 439. During the active call, and while it is being carried by the public domain, the IWF may carry the traffic between the public domain and the private domain through its media interfaces and media converter.

[0045] The process of FIG. 4 may also be applied to a handover from the public domain to the private domain. In such a case, the IWF receives the handover request instead through the MSC. The IWF then communicates with the IP PBX to establish a wireless channel between the enterprise network and the MS. After the channel is established, the active call is transferred to the established channel. In both cases, the IWF may appear to the public domain as an MSC. In other words, in such an embodiment, the IWF, using the public system interface, spoofs the protocols that an MSC would use for an inter-MSC handover.

[0046] FIG. 5 describes a handover similar to that described above from the perspective of the MS. In brief, the MS sends a handover request through the enterprise network to the IWF at block 510. The MS then receives a handover command through the enterprise network at block 520. Using the handover command, the MS then transfers the active call to the assigned cellular channel at block 530.

[0047] In generating the handover request, the MS may typically perform all of the steps that are normally involved in generating a handover request within the public domain. Such steps may include scanning the cellular system for available channels at block 511, and sending a cell identity list with the handover request at block 513 that includes measurements made on signals from different base stations.

[0048] At some point after the IWF and MSC have performed their appointed tasks, the MS can transfer its active call. In one embodiment, it will first receive a cellular channel assignment through the enterprise network at block 531. The assigned channel will typically be a traffic channel. It will then acquire the assigned cellular channel at block 533. After sending some signaling on the acquired cellular channel, it will send a completed handover message through that cellular channel at block 535. The MS may then signal the completed handover through the enterprise network to the PBX at block 537. This message will also be received at the IWF. The MS may then transfer its voice traffic to the successfully acquired cellular channel at block 539, and release the enterprise network traffic channel at block 541.

[0049] As with the example of FIG. 4, the example of FIG. 5 may be adapted for handovers from the public network to the enterprise network. In such a case, the MS will perform the necessary operations for finding a radio channel on the enterprise network. It may then send a handover request message through the public network. The MSC may interpret this as a request to handover to the IWF which is spoofing protocols that would be used by another MSC. After the IWF, IP PBX and MSC have performed the necessary operations, the MS will receive a handover command from the MSC. It can then transfer the active call from the public domain to an assigned channel in the enterprise network indicated in the handover command.

[0050] FIG. 6 shows a more complete and detailed sequence of messages that may be exchanged in a seamless handover from an enterprise system to a public system according to an embodiment of the invention. The diagram shows different elements of the enterprise system and the public system across the top row. Arrows between the elements show messages between the elements. Double sided arrows show traffic.

[0051] Line a shows an active call as a double sided arrow between an ES (enterprise station), such as a FS 133 or MS as shown in FIG. 1 and the E side of an MS 131. The MS is shown as having two parts labeled as G for a GSM cellular radio section and E for an enterprise radio. In line b, the quality of the WLAN enterprise radio signal drops below some threshold. There are a variety of different way for determining when this occurs. Some systems rely on measurements by the WLAN AP or base station and others use mobile station measurements while other systems may use a combination of both. At line c, the MS signals on its enterprise connection to the IP PBX that a handover is required.

[0052] The IP PBX and IWF then set about establishing a channel between the ES and the public network. The IP PBX forwards the handover request to the IWF for further handling. At line d the IWF allocates its own resources and assigns trunk identifiers such as CICs (Carrier Identification Code) to a particular enterprise network address. At line d, the address is sent to the IP PBX which instructs the ES to add this address to its active connections. At line f, the ES acknowledges the connection as established to the IP PBX and the IP PBX informs the IWF. At line g, this established connection is registered by the IWF.

[0053] The IWF also establishes a connection to the public domain. At line h, the handover request is sent to the public domain on a signaling channel as a request to prepare a handover. The MSC sees this as a request from another MSC of the system and responds back to the IWF on line i, the response including the handover command which specifies the licensed channel that the BSS has allocated for the handover. On line j, the IWF provides the connection information to the MSC, such as an ISUP (Integrated Services Digital Network User Part) IAM (Initial Address Message). The MSC, after making appropriate provisions to its network, can then reply at line k with the equivalent of an acknowledgement command, such as an ISUP ACM (Address Complete Message). The IWF then forwards the handover command received in line i through the IP PBX to the MS on its enterprise side.

[0054] The handover command provides the MS with the information it needs to access the public network. The MS then tunes its public network radio to the assigned channel and sends an access message at line l directly to a base transceiver station of the public network. The public network responds with the signals appropriate to establishing the wireless channel between the BTS and the MS (not shown).

[0055] When the MSC is signaled that the MS has successfully accessed the public network directly, it can signal the IWF that an access has been detected at line m and provide an ISUP ANM (Answer Message) to complete the ISUP signaling exchange. The IWF and MSC have now established a traffic channel between the ES and the MSC through the IWF media interfaces as shown on line o. Note that in this example, there are now two voice paths between the MS and the ES. The original path through the enterprise network alone is still active. The new path through the IWF to the public domain is also active. Briefly maintaining both paths reduces the chances that the call will be interrupted or dropped.

[0056] At line p, the MS has received traffic on the traffic channel from the ES and signals to the public network that the handover is complete. In some public networks, such a signal is sent in-band on the traffic channel. The MSC accordingly signals to the IWF that the handover is complete at line q. The IWF alerts the IP PBX and this allows the enterprise resources to be released.

[0057] To release the resources of the original call, the IP PBX signals the ES to delete the original enterprise connection of the active call at line r. The ES acknowledges the message at line s and the final traffic channel is established as shown at line u. The traffic path connects the ES wired or wirelessly through the enterprise network to the IWF and through the media interfaces of the IWF to the MSC. From the MSC, the path is connected through a cellular base station wirelessly to the MS.

[0058] FIG. 7 shows an example of handing an active call over to the enterprise network from the public network. FIG. 7 has the same format as FIG. 6 and the traffic path of lines a and b of FIG. 7 is the same as the traffic path of lines t and u of FIG. 6. The process of FIG. 7 may be performed independently of the process of FIG. 6. One process may be performed before the other and vice versa. From a user's perspective, the MS may allow a call that originated on the public network to be handed over to the enterprise network and it may also allow a call that originated on the enterprise network to be handed over to the public network. Once handed over to one domain it may also be handed back to the original domain and back again as needed to accommodate the movements of the user.

[0059] In FIG. 7, the active call is through the public licensed telecommunications service and at line c, the signal quality at the WLAN rises above some threshold. This may be determined by the WLAN AP, by the MS or by both. The MS then signals to the PBX that a handover is requested at line d. Note that in the example of FIG. 7, this message is sent using the enterprise side of the MS after the MS has gained access to the enterprise network. With the MS already on the network, the call can be carried by the enterprise network as soon as a connection is created with the ES.

[0060] The IP PBX allocates resources to accommodate the active call within the enterprise network and at line e assigns a new address to the ES that is already active in the call. At line f, the ES acknowledges the signal and at line g, the PBX signals the MS that the connection is complete by acknowledging the handover request. At line h, the MS transfers the traffic of the active call over to the enterprise network as indicated by the traffic path at line l.

[0061] The MS acknowledges the handover to the PBX at line i and the PBX can then clear unused resources. The PBX signals the ES to release the original connection to the MS at line j. This is acknowledged at line k. The PBX also signals the IWF to release the original connection with the ES at line l. The IWF releases internal resources at line m and then signals the MSC to release the connection to the IWF and to the MS at line n. The MSC then signals the IWF to release its channels from the original connection at line o and the IWF acknowledges to the MSC at line p. With the connection through the public network released, the IWF signals its acknowledgment back to the PBX at line q. The active call continues on the one open connection shown on line l.

[0062] FIG. 8 shows an example of communicating between the mobile station and the enterprise network through the public network. FIG. 8 has the same format as FIGS. 6 and 7 and the traffic path of lines a and b of FIG. 8 is the same as the traffic path of lines a and b of FIG. 7. The process of FIG. 8 may be performed independently of the processes of FIGS. 6 and 7. One process may be performed before the other and vice versa. From a user's perspective, the MS may receive signaling from the enterprise network while using the public network. When a call that originated on the enterprise network is handed over to the public network, the enterprise network may signal the MS (or vice versa). The signaling may allow all of the enterprise network features to be supported while the call is carried through the public network.

[0063] In FIG. 8, the active call is through the public licensed telecommunications service and at line c, there is a message for the mobile station 131 to be sent from the IP PBX 121 through the MSC 113. The signal can be conveyed to the mobile station wrapped in a standard cellular message envelope that flows unobstructed and unchanged between the IWF 147 and the mobile station. At line d, the IP PBX sends a request message or any other type of message to the IWF using its normal signaling protocol. At line e, the IWF wraps the message in a GSM message envelope and forwards the message to the MSC 113. One such wrapper is a GSM DTAP (Direct Transfer Application Part) Facility message, which in turn is encapsulated in a GSM MAP (Mobile Application Part) Forward Access Signaling message; however, other message types and formats may also be used.

[0064] The MSC 113 receives this message and interprets it as a conventional DTAP Facility message from another MSC. It removes the GSM MAP Forward Access Signaling wrapper. It then forwards the message to the addressed mobile station 113 at line f over the GSM air interface as a conventional GSM DTAP Facility message. The mobile station receives the message and at line g unwraps the message and interprets it based on the protocols of the originating enterprise system 121.

[0065] Similarly, the mobile station may send a message to the enterprise system through the MSC. At line h, the mobile station 131 generates a message to be sent to the IP PBX 121 of the enterprise system. The mobile station wraps the message in a GSM DTAP Facility message and at line i sends this message to the MSC over the GSM air interface.

[0066] The MSC interprets the message as a conventional message for the originating MSC, encapsulates the DTAP Facility message in a GSM MAP Process Access Signaling message, and forwards the message to the IWF 147 at line j. The IWF unwraps the message and transmits it to the IP PBX 121 in the appropriate format for the IP PBX at line k. The IP PBX may apply the message to its own processes or it may forward the message to another part of the enterprise system as indicated in the message. The message may be directed to another terminal on the system or to some other destination.

[0067] By wrapping messages in conventional GSM messages, a wide range of enterprise system messages can be conveyed between the enterprise system and the mobile station. If the call originated with the enterprise system and was then transferred to the MSC, then these messages may include call control signaling to end a call, signal that another incoming call to the mobile station is waiting, conference another caller, put a call on hold, forward the call to another enterprise station, to an external station, or to voice mail, or any other feature supported by the enterprise system. Other types of call control signaling may also be supported depending on the system. The signals listed here are provided as examples and the invention is not limited to the particular examples that are mentioned. By wrapping the messages in GSM messages, the enterprise system can continue to communicate with the mobile station using its native signaling protocols even though the messages must be conveyed through a different protocol system.

[0068] In one example, the IP PBX uses SIP [Session Initiation Protocol, an IETF (Internet Engineering Task Force) standard] signaling and the IWF wraps SIP messages into GSM DTAP Facility messages and then wraps the DTAP Facility messages in MAP Forward Access Signaling messages. However, other types of messages may be wrapped into DTAP Facility or other types of messages. Embodiments of the invention may be adapted to accommodate a wide range of different types of protocols and signaling conventions.

[0069] In a GSM protocol there are a number of different messages that can be used to encapsulate a message. As mentioned above, one such message is a DTAP Facility message. In other protocols, other messages may be used. One example of a DTAP Facility message is provided in the table below (Note: The complete specification of this message can be found in 3GPP TS 04.08 and 3GPP TS 04.80). The message is based on the Facility message of GSM that is designed to request or acknowledge a supplementary service. Alternatively, an unstructured supplementary service data (USSD) message format may be used. The message has an information element that specifies the supplementary service to be invoked and its associated parameters.

TABLE 1
Field	Value	Sequence
Protocol	Call Control	0011
Discriminator
Transaction	Varies	Any four bit value
Identifier
Message Type	Facility message	0011 1010
	type
Information	Facility IE type	0001 1100
Element
Length of IE	Varies	Depends on encapsulated
		message size
Component Type	Invoke type	1010 0001
Tag
Component Length	Varies	Depends on encapsulated
		message size
Invoke ID Tag	Invoke ID tag	0000 0010
Invoke ID Length	Length of Invoke ID	0000 0001
Invoke ID	Set by IWF or MS	Any one octet value
Operation Code	Operation code tag	0000 0010
Tag
Operation Code	Length of Op Code	Any
Length
Operation Code	Pre-defined for	A sequence of integers,
	this message	each encoded in binary
	forwarding service	format
Parameters	Encapsulated	Depends on the
	enterprise	encapsulated enterprise
	message	message

[0070] In Table 1, the Field indicates the type of message that is required in the GSM standard to create the DTAP Facility message. The value column is an example of a value that might be selected for each field and the Sequence column shows the sequence of bits corresponding to the selected value. Different values may be chosen depending on the application. The values shown are provided only as an example to illustrate an embodiment of the invention.

[0071] Most of the values and codes are set in accordance with the standard in order to emulate a conventional DTAP Facility message that will successfully be passed through. The transaction identifier is used to identify a particular transaction between the sender and the receiver and is set by the sender at the beginning of the transaction. The transaction identifier is not reused by that sender and receiver pair until the corresponding transaction is released. The length of message will be determined by the sender of the message based on its actual length. The operation code may be selected to have a value that distinguishes the encapsulated message from other standardized operations that may be sent in a conventional DTAP Facility message. The operation code may be used to instruct the MS or IWF to unwrap the message and interpret the unwrapped message as a SIP message.

[0072] Finally the message itself is transmitted. The encapsulated message is in a format appropriate for another protocol and may take any of the forms mentioned above. The example of Table 1 is provided to illustrate how a message from one protocol may be encapsulated in a message of another protocol. The particular protocols, messages and approach to the encapsulation may be modified to suit different applications.

[0073] FIG. 9 shows an example process flow according to an embodiment of the present invention. In FIG. 9, a mobile station formulates a message at block 911. This message is formulated in the format of a first telephony signaling protocol. As mentioned above, one such protocol used for Voice over IP systems is SIP. The message may be any one of the various types of messages mentioned above or any other type of call control or maintenance message.

[0074] At block 913, the mobile station wraps the message in a signaling protocol of a second telephony signaling protocol. This may be the protocol used by the switching center through which the mobile station is communicating. For example, if the mobile station is in a wireless call through a GSM base station, then the second telephony signaling protocol may be a GSM protocol. If the mobile station is in a call with a WCDMA (Wideband Code Division Multiple Access) base station or an 802.11 base station, then the message may be wrapped in a message format for that protocol.

[0075] At block 915, the mobile station sends the encapsulated message to the switching center to which it is connected. The switching center, at block 917, interprets this message as a standard message and forwards the message to another switching center. In one example, the call is controlled by the switching center that uses the first telephony protocol. The connected switching center, seeing that the message relates to call control or maintenance forwards the message to the switching entity that controls the call. The message may be further encapsulated according to the applicable protocols for communication between switching entities.

[0076] At block 919, the switching entity that uses the first telecommunications protocol receives the message and reads or applies it according to the standards of its native protocol. In one example, an intermediate device, such as the IWF shown in the Figures unwraps the message so that the message is presented to the switch in the format of the first telecommunications protocol. In another example, the switching entity unwraps the message.

[0077] While FIG. 9 shows messages flowing from a subscriber terminal to a switch, the switch may also send messages to the mobile station as suggested by FIG. 8. In either direction the messages may be requests or acknowledgments. The message stream may be originated by either device. The wrapping or encapsulating may similarly be performed either by the device that generates the message or by some other device. By encapsulating the message, it may be carried by the second telephony system without any changes or accommodations being made to the second telephony system that carries the message.

[0078] The particular sequence of events and types of signals are provided as examples only. The example of FIGS. 6, 7 and 8 are presented in the context of a VoIP IP PBX and a GSM cellular network. Appropriate modifications may be made to comply with other types of networks.

[0079] The particular sequence of events and types of signals are provided as examples only. The example of FIGS. 6 and 7 are presented in the context of a VoIP IP PBX and a GSM cellular network. Appropriate modifications may be made to comply with other types of networks.

[0080] It is to be appreciated that a lesser or more equipped interworking facility, mobile station, enterprise station, enterprise network, and PBX than the examples described above may be desirable for certain implementations. Additional or different components, interfaces, buses and capabilities may be used and additional devices may be added to any of these components. Some of the illustrated components may also be removed from the devices. The configuration of the interworking facility, mobile station, enterprise station, enterprise network and PBX may vary with different implementations depending upon numerous factors, such as price constraints, performance requirements, technological improvements, or other circumstances.

[0081] Although the description of the various embodiments refers primarily to transitioning active calls between a VoIP enterprise network and a GSM cellular telecommunications system, the various embodiments may also be used with other types of enterprise communications systems and with other types of public telecommunications networks. The various embodiments may be applied to voice networks, data networks and combined networks whether they are circuit switched or packet switched.

[0082] Embodiments of the present invention may be provided as a computer program product which may include a machine-readable medium having stored thereon instructions which may be used to program a control station, a microcontroller or other electronic device to perform a process. The machine-readable medium may include, but is not limited to, floppy diskettes, optical disks, CD-ROMs, and magneto-optical disks, ROM's, RAM's, EPROM's, EEPROM's, magnet or optical cards, flash memory, or other type of media or machine-readable medium suitable for storing electronic instructions. Moreover, embodiments of the present invention may also be downloaded as a computer program product, wherein the program may be transferred from a remote computer or controller to a requesting computer or controller by way of data signals embodied in a carrier wave or other propagation medium via a communication link (e.g., a modem or network connection).

[0083] In the description above, numerous specific details are set forth. However, embodiments of the invention may be practiced without these specific details. For example, well-known equivalent components may be substituted in place of those described herein, and similarly, well-known equivalent techniques may be substituted in place of the particular processes disclosed. In other instances, well-known structures and techniques have not been shown in detail to avoid obscuring the understanding of this description.

[0084] While the embodiments of the invention have been described in terms of several embodiments, those skilled in the art will recognize that the invention is not limited to the embodiments described and illustrated, but may be practiced with modification and alteration within the spirit and scope of the appended claims. The description including the drawings is thus to be regarded as illustrative instead of limiting.