Abstract:
The present invention provides a system and method for reliably transferring Dual Tone Multiple Frequency (DTMF) signals originating at a MS through an IP based GSM network. In general, when a MS sends a DTMF request, it is processed in the IP network by a logical application module in a MSC, which, based on the disclosed processing, activates another logical application module in an appropriate gateway (for independent, remote, tone generation), and then the logical application module in the gateway directs the production of the DTMF signal towards the interworking or destination network.

Description:
TECHNICAL FIELD 
     The invention relates generally to telecommunications and more particularly to a system and method of sending Dual Tone Multiple Frequency (DTMF) tones through a Global System for Mobile Communications (GSM) network having an Internet Protocol (IP) based backbone transport network. 
     BACKGROUND OF THE INVENTION 
     Dual Tone Multiple Frequency (DTMF) tones are used to allow a telephone network user to, for example, interact with voice mail systems, to perform electronic banking, or to direct the functioning of an Advanced Intelligence Network (AIN) service. Traditionally, in a Public Switched Telephone Network (PSTN), DTMF tones are generated by the terminal (hand set). However, in GSM, if DTMF tones were transmitted from a Mobile Station (MS) handset, the DTMF signals would be mutilated by the GSM voice transcoder, and could not pass recognizably through the network. Thus, for a MS in a GSM network to send DTMF tones, a tone generation request message (rather than the actual tone) is sent from the MS to a Mobile Switching Center (MSC). The tones are then typically generated by the MSC and sent to a destination device. 
     Networks utilizing Internet Protocols (IP) are readily available, offer defined system interface protocols, and have the ability to reliably transmit voice data. IP-based transport networks may also simultaneously support the transport of other data types, such as Internet traffic or voice over IP (VolP) traffic for wireline networks. IP transport networks typically have lower capital costs, lower recurring costs, and lower tariffs than traditional circuit-switched networks. Accordingly, IP networks may soon be used as a communications backbone suitable for providing a platform to carry GSM network traffic, thus providing the same functionality as a circuit-switched network at lower cost. The benefits provided by the IP network, however, comes at a cost. 
     Since the voice data is being carried through an IP network, the circuit-switched devices in the MSC are no longer operable. Therefore, the MSC cannot directly insert DTMF tones on request from the MS. Therefore, there does not exist a reliable system or method of transferring a DTMF tone through an IP based GSM network. Therefore, there exists the need for a system and method of sending DTMF tones reliably through a GSM based telecommunications network that uses an IP network as a backbone. 
     SUMMARY OF THE INVENTION 
     The present invention provides a system and method for reliably transferring DTMF tones through an IP based GSM network. In general, when a MS sends a DTMF request (typically a DTAP message called “Start DTMF”), it is processed in the IP network by an MSC. The MSC activates an internal software module and an appropriate gateway (for independent, remote, tone generation), and then a processor in the gateway directs the production of the DTMF signal towards the destination network or MS. 
     According to one aspect of the present invention, provided is a system for sending DTMF tones through an IP based GSM network. The system generally comprises a mobile switching center having a first logical application module which receives a Direct Transfer Application Part (DTAP) message and converts the DTAP message into a Device Control Message (DCM). The system also contains a gateway coupled to the mobile switching center and the IP transport network, and which has a second logical application module that directs the generation of the tone. 
     The system may provide the capacity for the first logical application module to process the DTAP message and send a corresponding device control message to the second logical application module. In addition, the second logical application module may send a failure message to the first logical application module when tone generation is not possible to attempt or the attempt fails (e.g. congestion in tone-generating equipment). The second logical application module may also select the tone generation method and direct the creation and routing of the tone to the interworking or destination communication system. The gateway of the system may be in communication with a PSTN, an IP network, or another MS. 
     The method of supporting DTMF tone sending in an IP based GSM network utilizes the steps of receiving a DTAP command from a GSM MS, converting the DTAP command at the MSC into a device control message to the gateway, instructing a tone generator to generate a tone, and sending the tone to the interworking communication system. The interworking communication system utilized in this method could be a PSTN or other circuit-switched network. 
     Likewise, another method of supporting DTMF tone sending in a IP based GSM network utilizes the steps of receiving a DTAP command from a GSM MS, converting the DTAP command at the MSC into a device control message to the gateway, and selecting a tone generator method compatible with the interworking IP network. The tone generator method could comprise the steps of ordering a tone generator to generate a tone delivered as voice payload to the interworking IP network. The voice payload may be in the form of UDP, RTP, or other standard IP-based payload format, in accordance with the voice payload format of the interworking IP network. Alternatively, the tone generator method could comprise the step of converting the device control message to an IP telephony control message that is routed to the interworking IP network&#39;s control node (e.g. an H.323 Gatekeeper) for this call. 
     Alternatively, another method of supporting DTMF tone sending in an IP based GSM network could comprise the steps of receiving a DTAP command from a GSM MS, converting the DTAP command at the MSC into a device control message to the gateway, ordering a tone generator to generate a DTMF tone, and delivering the DTMF tone from the tone generator to a destination GSM MS. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other aspects of the invention, including specific embodiments, are understood by reference to the following detailed description taken in conjunction with the drawings in which: 
     FIG. 1 shows a prior art GSM configuration; 
     FIG. 2 illustrates a GSM network having an Internet Protocol (IP) network for its backbone; 
     FIG. 3 is a flow diagram showing the steps for communicating a DTMF tone from a mobile station in a GSM network having an IP backbone to a PSTN; 
     FIG. 4 provides a block flow diagram illustrating the steps for communicating a DTMF tone from a mobile station in a GSM network having an IP backbone to an IP based network; and 
     FIG. 5 depicts the flow of logic for communicating a DTMF from an MS to another MS across a GSM having an IP backbone. 
    
    
     References in the detailed description correspond to like references in the figures unless otherwise indicated. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 shows a prior art GSM network denoted generally as  100 . Within the network  100 , a MS  120  communicates with a Base-station Transceiver Substation (BTS)  130  via radio communications (illustrated in FIG.  1  and other Figures as a lightning bolt). The BTS  130  then communicates with a Base Station Controller (BSC)  140 . The BSC  140  then routes the communications between the BTS  130  and a Mobile Switching Center (MSC)  150 . Although only one BTS  130  is shown, in a typical GSM network, a plurality of BTSs are connected to a BSC. Likewise, a plurality of BSCs are typically attached to a MSC  150 . The MSC  150  may then be connected to a standard GSM circuit switched network backbone which carries calls from the MS  120  to a destination device through a destination network  160 , (which may be a PSTN, an IP, or a PLMN (Public Land Mobile Network). 
     In a prior art GSM network, DTMF tone sending is not done directly by a MS. This is because a DTMF tone, if sent by a MS, would be mutilated by the transcoding processor. Because they are mutilated by the voice transcoder, the tones would not then be recognizable by an application that needs to interpret them. 
     Instead, when a user of the MS  120  attempts to send a tone from the MS  120 , instead of the tone being sent from the MS  120  to the BTS  130 , a Direct Transfer Application Part (DTAP) message, “Start DTMF”, is sent from the MS  120  to the BTS  130 . The Start DTMF message routes through the BSC  140 , and then to the MSC  150 . The MSC  150  then connects an appropriate internal tone sending device and instructs the tone sending device to insert a tone into the speech path towards the network  160 . If the MSC  150  detects that the tone sending was successful, the fact that the tone sending was successful is reported to the MS  120  with a “Start DTMF Acknowledge” message. If the tone generation fails, the failure is reported to the MS  120  using a “Start DTMF Reject” message. 
     FIG. 2 illustrates a GSM network having an IP network  270  for its backbone. MS  220  is in communication with BTS  222  that is wire connected to an IP network  270 . MS  220  may communicate with a variety of destination networks. Accordingly, another mobile station  266  is shown in radio communication with another BTS  264  that is wire coupled to the IP network  270 . In addition, MSC  230  having a DTMF MSC processor (DMSCP)  232  therein is in communication with the IP network  270 . 
     Also attached to the IP network  270  is a Gateway (GW)  260  having therein a DTMF Media Gateway Processor (DMGP)  262  for directing tone generation and signal evaluations. Another GW  240  is coupled between the IP network  270  and a PSTN  244 , the GW  240  having therein a DMGP  242  for directing the routing of a tone to the PSTN  244  and for evaluating whether or not the tone was successfully sent. Furthermore, the system of the present invention comprises a GW  250  coupled between the IP network  270  and an Internet Protocol based Network  254 , the GW  250  having therein a DMGP for directing the generation of a tone into the IP network  254  and for evaluating signal sending success. Thus, from FIG. 2, it can be seen that the present invention can be used to route a tone originating from a mobile station through an IP based network backbone, and then send the tone to, for example, a PSTN, an IP, or another MS. 
     CASE ONE 
     FIG. 3 is a flow diagram that shows the steps for communicating a DTMF tone from a MS  220  to a PSTN  244  in a GSM network having an IP backbone  270 . In an initialization, step  310 , the MS  220  sends a “Start DTMF” message to the Logical Application Module (LAM) known as the DTMF MSC Processor (DMSCP)  232 , which resides in the MSC  230 . Next, through a conversion, step  312 , the DMSCP  232  processes the start DTMF into a device control message, which is then transported to a LAM called a DTMF Media Gateway Processor (DMGP)  242  (the DMGP  242  is stored and executed in the GW  240 ) in step  314 . 
     Next, the DMGP  242  checks to determine if the generating device (not shown) is available in a ready check, step  320 . If the device is not ready or able to send a DTMF tone, the DMGP  242  sends a notice to the MSC  230  of the failure in a rejection notice, step  324 . To report the failure to the MS, the DMSCP  232  then sends a “Start DTMF Reject” notice to the MS  220  in a MS rejection notice, step  326 . 
     If the DMGP  242  is ready, in an appropriate state, and has available tone resources, then the DMGP  242  directs the tone generation. How the tone is generated depends on the devices available for tone generation, which are analyzed in a gateway tone, step  330 . In this case, if the GW  240  can generate a tone, then the GW  240  generates the tone in a GW tone generation device, step  332 . Then, the tone is routed to the appropriate destination device in a tone routing, step  338 . If the GW  240  cannot generate a tone, then the DMGP  242  commands a tone generation device, such as another GW  260 , to generate the tone in a tone command, step  334 . In a tone generation, step  336 , the tone generation device produces the tone. The tone routing is then directed by the DMGP  242  in a tone routing step  338 . 
     Following the tone routing, step  338 , the DMGP  242  detects whether or not the tone was sent in a success check, step  340 . If the tone generation is unsuccessful the DMGP  242  sends a rejection notice to MSC  230  in a rejection notice, step  324 . Next, the DMSCP  232  sends a “Start DTMF Reject” notice to the MS  220  to report the failure in a MS rejection notice, step  326 . If the tone generation is successful the DMGP  242  notifies the DMSCP  232  of the successful tone transmission in a success notice, step  342 . Then, the DMSCP  232  notifies the MS  220  of the tone generation by sending a “Start DTMF Acknowledge” message in a MS success notice, step  344 . 
     CASE TWO 
     FIG. 4 provides a block flow diagram illustrating the steps for communicating a DTMF tone from a MS  220  to an IP based network  254  through a GSM network having an IP backbone  270 . In an initialization, step  410 , the MS  220  sends a “Start DTMF” message to the logical application module DMSCP  232  in the MSC  230 . Next, through the conversion, step  412 , the DMSCP  232  processes the start DTMF into a device control message, which is transported to a LAM, DMGP  252 , in the GW  252  in step  414 . 
     The DMGP  252  then checks to determine if the generating device (not shown) is available in a ready check, step  420 . If the device is not ready or able to send a DTMF tone, the DMGP  252  sends a rejection notice to the MSC  230  in a rejection notice, step  424 . The DMSCP  232  then sends a “Start DTMF Reject” notice to the MS  220  to report the transmission failure in a MS rejection notice, step  426 . 
     If the DMGP  252  senses that the generating device can send a DTMF tone, then the DMGP  252  directs the tone generation, depending on available tone generation techniques, which are analyzed in the gateway, step  430 . If the GW  250  shall generate a tone directly, as in Case One, the GW generates the tone in a GW tone generation, step  432 , which places UDP, RTP, or other IP-format data packets into the IP network data stream. The tone is then routed to the appropriate destination device in a tone/message routing step, step  438 . If the GW  250  shall not generate a tone, but shall send a tone request message, then the DMGP  252  composes the request message toward the destination network, step  436 . The routing of the message is accomplished in the tone/message routing, step  438 . 
     Following the tone/message routing, step  438 , the DMGP  252  detects whether or not the tone/message was sent, in a success check, step  440 . If the tone generation fails, the DMGP  252  sends a rejection notice to MSC  230  in a rejection notice, step  424 . Next, the DMSCP  232  sends a “Start DTMF Reject” notice to the MS  220  to report the failure in a MS rejection notice, step  426 . If the tone generation is successful, the DMGP  252  notifies the DMSCP  232  of the tone in a success notice, step  442 . Then, the DMSCP  232  notifies the MS  220  of the tone generation by sending a “Start DTMF Acknowledge” message in a MS success notice, step  444 . 
     CASE THREE 
     FIG. 5 depicts the flow of logic for communicating a DTMF tone from a MS  220  to another MS  266  across an IP based backbone  270  in a GSM network. In an initialization, step  510 , the MS  220  sends a start DTMF message to the LAM DMSCP  232  in the MSC  230 . Next, through the conversion step the DMSCP  232  changes the.start DTMF into a device control message, which is transported to a LAM, DMGP  262 , which is in the GW  260 , in step  514 . 
     The DMGP  262  then checks to determine if the generating device (not shown) is available in a ready check, step  520 . If the destination device is not ready or able to receive a DTMF tone, the DMGP  262  sends a rejection notice to the MSC  230  in a rejection notice, step  524 . The DMSCP  232  then sends a “Start DTMF Reject” notice to the MS  220  to report the failure in a MS rejection notice, step  526 . If the generating device can send a DTMF tone, then the DMGP  262  directs the tone generation. 
     Tone generation is implemented by first issuing a generate tone command in a tone command, step  534 . The selected tone generating device then produces the tone in a tone generation, step  536 . Next, the DMGP  262  routes the tone to the appropriate destination device in a tone routing, step  538 . 
     Following the tone routing, step  538 , the DMGP  262  detects whether or not the tone was sent in a success check, step  540 . If the tone generation step fails, the DMGP  262  sends a rejection notice to the MSC  230  in a rejection notice, step  524 . The DMSCP  232  then sends a “Start DTMF Reject” notice to the MS  220  to report the failure in a MS rejection notice, step  526 . If the tone generation is successful, the DMGP  262  notifies the DMSCP  232  of the tone in a success notice, step  542 . Then, the DMSCP  232  notifies the MS  220  of the tone generation by sending a “Start DTMF Acknowledge” message in a MS success notice, step  544 . 
     While the invention has been described with preferred embodiments it should be understood that modifications will become apparent to those of ordinary skill in the art and that such modifications are intended to be included with the scope of the invention as defined by the following claims.