Abstract:
An apparatus in one example comprises a receiver of a first mobile switching center. The receiver is configured to receive an input signal in a first encoding format. The input signal has an input payload. The first encoding format is a dual-mode InterSystem Link Protocol (ISLP)/Enhanced Variable Rate Coding (EVRC) codec. The apparatus further comprises a transcoder operatively coupled to the receiver. The transcoder is structured to transcode in a single channel the first encoding format to a second encoding format. The transcoder is configured to generate an output signal in the second encoding format for transmission over an internet protocol (IP) network to a second mobile switching center based on the input signal. The output signal has an output payload based on the input payload. The transcoder is configured to switch between a default voice handling mode for the EVRC codec and a clear channel mode for the ISLP codec to form the output payload.

Description:
TECHNICAL FIELD 
     The invention relates generally to telecommunication systems, and more particularly to methods of transcoding between a dual-mode InterSystem Link Protocol/Enhanced Variable Rate CODEC (ISLP/EVRCx) (where EVRCx is either EVRC-A or EVRC-B) codec and a G711 codec in an Internet Protocol (IP) Packet Network. 
     BACKGROUND 
     A coder-decoder (CODEC) is essentially a data compression algorithm that selectively throws away information that it deems to be unimportant, while retaining the data that it deems necessary. The CODEC plays important role in the communications link. The CODEC must be robust enough to withstand a certain degree of data degradation during transmission. The better the CODEC is able to recover from bit errors, the more natural the reproduction will be over a wide range of conditions. 
     The original Code Division Multiple Access (CDMA) CODEC was not particularly robust, and as such it made even low Bit Error Rates audible to a discerning listener. CDMA providers began implementing a new CODEC called EVRC (which stands for Enhanced Variable Rate CODEC). EVRC permits more compressed signals (subscribers) to be stuffed into the same bandwidth. EVRC manages to produce reasonable audio quality in only 8 kilobits. Since individual EVRC users consume less bandwidth than users of the old CODEC, a CDMA “carrier” can accommodate more of them. 
     SUMMARY 
     Existing solutions for transcoding between a dual-mode InterSystem Link Protocol (ISLP)/EVRCx (where EVRCx is either EVRC-A or EVRC-B) codec and a G711 codec in an Internet Protocol (IP) Packet Network suffer from a variety of disadvantageous limitations. For example, such solutions for transcoding between dual-mode ISLP/EVRCx codec and a G711 codec require the usage of two distinct channels. That is, while ultimately packets containing EVRCx voice or ISLP datagrams are transcoded to Packets containing G.711 voice or ISLP adapted data encapsulated in G.711 packets, respectively, and similarly, packets containing G.711 voice or ISLP adapted data encapsulated in G.711 packets are to be transcoded to Packets containing EVRCx voice or ISLP datagrams respectively, two distinct channel are required to accomplish that task. One channel performs a packet to and from circuit function to transcode between EVRCx voice or ISLP datagrams and Time Division Multiplexing (TDM) data. A second channel performs a packet to and from circuit function to transcode between G.711 voice or ISLP adapted data encapsulated in G.711 packets and TDM data. A TDM network is required to connect the channel resources together. The two channels are connected via the TDM network to provide the overall solution. 
     Thus, current solutions suffer from drawbacks including: requiring two (2) channel resources to perform the overall solution, and requiring a TDM network to connect the channel resources together. In addition, the latency of each channel is on the order of 40 ms, so the overall latency for the two (2) channel solution is approximately 80 ms. For a mobile to mobile call using this solution at each end, the total latency will approach 340 ms which will contribute to a poor voice quality/user experience. 
     Embodiments provided herein implement the transformation between data formats within a single channel element. By enabling transcoding in a single channel, the software framework scheduling algorithm may be optimized to sequentially process each step of the transcoding operation. As a result, the latency contribution of the transcoding function may be reduced. Furthermore, the transcoding channel described herein is also independent of any TDM network, and thus can be used as a standalone solution in an IP Packet network. 
     One implementation provided herein encompasses an apparatus, which comprises: a receiver configured to receive an input signal in a first encoding format, the input signal having an input payload; and a transcoder operatively coupled to the receiver, the transcoder structured to transcode in a single channel the first encoding format to a second encoding format, the transcoder configured to generate an output signal in the second encoding format based on the input signal, the output signal having an output payload; and wherein the transcoder is configured to switch between providing encrypted data in the output payload and non-encrypted data in the output payload. 
     Another implementation encompasses an apparatus, which comprises: a receiver configured to receive a respective input signal having a respective payload in a first encoding format; and a transcoder that effects transcoding, in a single channel, of the first encoding format to a second encoding format, the transcoder configured to generate an output signal having a payload in the second encoding format based on the input signal, wherein the first encoding format is InterSystem Link Protocol (ISLP), and wherein the second encoding format is G.711. 
     A further implementation encompasses an apparatus, which comprises a first network system operatively coupled to a second network system via an IP network. The first network system has: a receiver, configured to receive an input signal having a payload in a first encoding format, that accepts a respective first signal having a respective payload in the first encoding format; a transcoder that effects transcoding, in a single channel, of the first encoding format to a second encoding format, the transcoder configured to generate a second signal having a payload in the second encoding format based on the input signal; and transmitter for sending the second signal on the IP network. The second network system has: a receiver, configured to receive an input signal having a payload in a first encoding format, that accepts the second signal from the IP network, the second signal having the respective payload in the second encoding format; and a transcoder that effects transcoding, in a single channel, of the second encoding format to the first encoding format, the transcoder configured to generate a further first signal having a payload in the first encoding format. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The features of the embodiments of the present method and apparatus are set forth with particularity in the appended claims. These embodiments may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which: 
         FIG. 1  depicts Mobile-to-Mobile call with G.711 in an example system. 
         FIG. 2  depicts Mobile-to-Mobile call with G.711 in an example system, according to descriptions of methods and apparatuses described herein. 
         FIG. 3  is a general diagram of an embodiment according to the descriptions of the method and apparatus described herein. 
         FIG. 4  depicts a mobile-to-mobile bearer path example for an MSC. 
         FIG. 5  depicts a Mobile-to-Mobile Bearer Path example for an IOS BSC/MSC. 
     
    
    
     DETAILED DESCRIPTION 
     The following abbreviations are used herein: 
     AEC acoustic echo control 
     API application programming interface 
     BSC base station controller 
     CDMA code division multiple access 
     CV circuit vocoders 
     DSP digital signal processor 
     DTMF dual tone multifrequency 
     EVRC enhanced variable rate coding 
     IOS inter-operability standard 
     IP Internet protocol 
     ISLP intersystem link protocol 
     MMC mobility manager center 
     MSC mobile switching center 
     NPH network protocol handler 
     OFI optical facility interface 
     PCM pulse code modulation 
     PFS packet frame selector 
     PHV7 protocol handler for voice 
     PS professional services 
     PV packet vocoder 
     SH speech handlers 
     TDM time division multiplexing 
     TS time slot 
     VT voice transparency 
     VTTS voice transparency transmission system 
     According to the methods and apparatuses described herein, instead of performing ISLP encoding in one channel and transcoding between the TDM and G.711 in another channel, one single channel is utilized instead. A speech handler and a circuit vocoder are combined into a packet vocoder. A DTMF portion may be added on the circuit vocoder. 
     Embodiments according to the present method and apparatus provide, for example, a low-latency method to transcode between a dual-mode ISLP/EVRCx (where EVRCx is either EVRC-A or EVRC-B) codec and a G.711 codec in an Internet Protocol (IP) Packet Network. Packets containing EVRCx voice or ISLP datagrams may be transcoded to Packets containing G.711 voice or ISLP adapted data encapsulated in G.711 packets, respectively. Similarly, packets containing G.711 voice or ISLP adapted data encapsulated in G.711 packets may be transcoded to Packets containing EVRCx voice or ISLP datagrams, respectively. 
     One feature of the embodiments described herein is that both of two channel functions are combined into a single channel, the transformation between data formats taking place within the same channel element. Also, by combining both of the channel functions into a single channel, the software framework-scheduling algorithm is now optimized to sequentially process each step of the transcoding operation. Such optimization of the function reduces its latency contribution. In one example embodiment, this optimization will reduce the latency contribution of the function from 80 ms to 40 ms. The resultant combined transcoding channel is also now independent of any TDM networks, and can be used as a standalone solution in an IP Packet network. As another benefit, embodiments provided support an ISLP codec in an IP Packet network. 
     Embodiments of the present method and apparatus may have, for example, the following capabilities: Support for voice transparency feature for the packet loop-around and G.711 IP trunking configuration (International Federation for Information and Documentation (FID) 13025.3); Support for media negotiation only to G.711 for the mobile-to-mobile calls that are established between switches (requires G.711 between MSCs) (FID 13025.3); Provide the packet vocoder (PV) with the capabilities of performing “ISLP adaptation” or “reverse ISLP adaptation” for handling the VTTS calls (FID 13025.3); and Support for AEC on the PHV7 PVs (FID 13025.4). 
       FIG. 1  depicts Mobile-to-Mobile call w/G.711 in an example system, DURING ALERTING. Mobile A  102  communicates with mobile B  104  via a base station  106 , a first MSC  108 , an IP network  110 , a second MSC  112  and a base station  114 . The first MSC  108  is operatively coupled to a first MMC  116  via a MMC-DC8 interface  118 . The second MSC  112  is operatively coupled to a second MMC  120  via a MMC-DC8 interface  122 . 
     The first MSC  108  may have a PFS  124 , which receives an input signal having a payload in a first encoding format. The PFS  124  is operatively coupled to a PV  126 , for example PHV7 PV  126 , which may for example convert EVRC to G.711. An EVRC packet stream may contain ISLP encrypted data. The PHV7 PV  126  may be operatively coupled to a series pair of NPH  128 ,  130  for packet loop around (G.711), followed by a PHV7 PV  132 . The PHV7 PV  132  is operatively coupled to a NPH  134  that transmits an output signal having a payload in a second encoding format over IP network  110 . 
     The second MSC  112  may have an NPH  136 , which receives a signal from the IP network  110 . The NPH  136  may be operatively coupled to a PHV7 CV  138 , which may be operatively coupled to a PFS  140 . The base station  114  may be operatively coupled to the PFS  140  in the second MSC  112 . 
       FIG. 2  depicts Mobile-to-Mobile call w/G.711 in an example system, TALKING according to an embodiment of the present method and apparatus. Mobile A  202  communicates with mobile B  204  via a base station  206 , a first MSC  208 , an IP network  210 , a second MSC  212  and a base station  214 . The first MSC  208  may be operatively coupled to a first MMC  216  via a MMC-DC8 interface  218 . The second MSC  212  may be operatively coupled to a second MMC  220  via a MMC-DC8 interface  222 . 
     The first MSC  208  may have a PFS  224 , which receives an input signal having a payload in a first encoding format. The PFS  224  may be operatively coupled to a PHV7 PV  226 , which may for example convert EVRC to G.711. The PHV7 PV  226  may be operatively coupled to a NPH  234  that transmits an output signal having a payload in a second encoding format over IP network  210 . 
     The second MSC  212  may have an NPH  236 , which receives a signal from the IP network  210 . The NPH  236  may be operatively coupled to a PHV7 PV  238 , which may be operatively coupled to a PFS  240 . The base station  214  may be operatively coupled to the PFS  240  in the second MSC  212 . 
     Embodiments according to the descriptions provided herein may include one or more of the following: 
     Supported MSC, such as integrated MSC, single-DCS and multiple-DCS; 
     Supported PS platform, such as PS and PS-C platforms; 
     Supported PHV, PHV6 (PFS) and PHV7 (PFS, PV, and CV); 
     Supported call origination and call termination (with ‘conditional’ loop-around capability such as that implemented by Transcoder Free Operation/Remote Transcoder Operation (TrFO/RTO) features); 
     Supported media negotiation only to G.711 for calls established between PSs; 
     Supported bearer interworkings, such as, pkt-in to pkt-out, pkt-in to ckt-out, ckt-in to pkt out, and ckt-in to ckt-out; 
     Supported transcoding capabilities, such as, EVRC-to-G.711, G.711-to-EVRC, G.711-to-G.711, EVRC-to-PCM, PCM-to-EVRC, PCM-to-G.711, G.711-to-PCM; 
     An example scenario of one embodiment is as follows: 
     The following pre-conditions apply to the example scenario: an EVRC call has been successfully established between mobile A and mobile B; the established call is not involved in any service; and A and B decide to apply VT to the call, and both A and B push the VT button. 
     The serving BS receives a VT request message (i.e., ServiceRequestMsg) (e.g., 80b0H or 80a0H) from the traffic channel. 
     If the associated Feature Control (FAF) is enabled, the serving BS sends a VT Service Request message (e.g., FS_Transport message) to the PS via the Cell-PS interface. 
     Upon receipt of the VT Service Request message from the serving BS, PS would verify if this is a SH call (SH assigned) or a PFS call (PFS assigned). If it is a PFS call, PFS would transparently transfer the received data (VTTS-encrypted data) to the egress side. 
     If this is a PFS call, the inserted Packet or Circuit Vocoder (PV or CV) will be notified of the VTTS mode change. In this example, PV should perform ISLP adaptation and should convert EVRC to G.711 (for PV) or TDM (for CV). The ISLP-adapted data stream would then be transmitted to the network. 
     PS would then return with an ACK message (FS_Transport message) to the serving BS. 
     The SH calls may follow the mechanism developed by FID 13025.2. Failure scenarios may follow the mechanism developed by FID 13025.2. 
     A Null PV (if inserted) transparently transfers the data received from the ingress side to the egress side. 
     Upon receipt of the ISLP-adapted data stream, CV (if inserted) may process the data based on the codec used by the opposite side (Supported in FID 13025.2). If the opposite side uses un-compressed codec (e.g., G.711 or PCM), CV should transparently send the ISLP-adapted data to the egress side, and should switch to the ‘Clear Channel’ mode. If the opposite site uses compressed codec (e.g., EVRC), CV should perform reverse ISLP adaptation and then send the “VTTS-encrypted data” to the egress side. 
     In addition, the PS call processing may be notified of the VTTS mode change (for debugging purpose). 
     For FID 13025.4, support may be added of AEC on PHV7 PV&#39;s as follows: 
     Use same AEC algorithm currently deployed for SH and CV channels on PHV7; 
     Support EVRC to and from G711 PV type (no capacity degradation); 
     Support usage of AEC on both sides of a PV; near-end (EVRC side) cancels acoustic echo from Mobile, and far-end (G711 side) cancels acoustic echo from Mobile/PHS on other side of the network if no AEC enabled on other side of the network; 
     Added to FC/PS/DSP interfaces for PV call setup and PV switch codec; 
     New provisioning field to enable PV&#39;s; near-end (EVRC-side of PV) enable (near-end bulk delay (60-800 ms), and near-end echo path dispersion (5-200 ms)); 
     Far-end feature (G711-side of PV) enable; far-end feature Bulk Delay (e.g. 60-800 ms), and far-end feature echo path dispersion (e.g., 5-200 ms)); and 
     AEC is automatically disabled for calls in VTTS mode. 
       FIG. 3  is a general diagram of an embodiment according to methods and apparatuses described herein. A first MSC  306  is operatively coupled to a second MSC  308  via a network  310 , which may be for example an IP network. The first MSC  306  may have a receive module, for example a PFS, that receives an input signal  302 . The input signal  302  may, for example, have voice packets. The receive module  312  may be operatively coupled to a transcode module  314  that is operatively coupled to a transmit module  316 . The transcode module may be, for example, a packet vocoder. The transmit module may be, for example, an NPH. An output signal from the transmit module  316  may be in the G.711 format. 
     The second MSC  308  may have corresponding components receive module  318 , transcode module  320  and transmit module  322  that provides an output signal  304  that may have, for example, voice packets. Of course, for transmission of signals in the opposite direction functions of the modules are correspondingly reversed. 
     The above-described switching function of the transcoder is described in the embodiments of the packet vocoder/transcoder paradigm. However, embodiments may alternatively use a DTMF method of triggering the switch in a TDM-to-packet/packet-to-TDM paradigm. Embodiments may further include voice transparency. 
     In general Speech Handlers (SHs) are used for all mobile calls. The TrFO feature is turned on for the MSC but no cells have TrFO active. SHs provide acoustic echo cancelling for the near end mobile. G.711/IP trunking is provided by using Circuit Vocoders (CVs) to interwork circuit-to-packet and by using NPHs to connect to the packet network. CVs are setup using the existing G.711 codec. Interaction with VTTS described later. For the traditional MSC configuration, loop-around circuit trunks are used at both the originating MSC and the terminating MSC to connect the SHs to the CVs. The terminating MSC treats all calls as “circuit redirection”. For the IOS configuration, A2 trunks are used at both the originating MSC and the terminating MSC in place of loop-around trunks. 
       FIG. 4  depicts a mobile-to-mobile bearer path example for an MSC. Communication is provided in this example between mobile A  402  and mobile B  404 . 
     An INCALL or first MSC  406  performs an HLR query and routes calls to at least a second MSC  408  over an IP core  410  (e.g., via Top Level Domain Name (TLDN) routing). CVs  412 ,  414  are setup at call establishment time with a standard G.711 codec. The CVs  412 ,  414  provide echo cancellation, gain adjustment, etc. and may be PHV7 CVs. The terminating or second MSC  408  treats all incoming packet calls via “circuit redirection”. 
     Each MSC  406 ,  408  has a SH  416 ,  418  operatively coupled to a series pair of OFIs  420 ,  422  and  424 ,  426 , which are in turn operatively coupled to the PHV7 CV  412 ,  414  that in turn is operatively coupled to the NPH  428 ,  430 . The NPHs  428 ,  430  are operatively coupled to the IP core  410 . 
       FIG. 5  depicts a Mobile-to-Mobile Bearer Path example for an IOS BSC/MSC. Communication is provided in this example between mobile A  502  and mobile B  504 . A first IOS BSC  505  is operatively coupled to a first IOS MSC  506 . Signals from mobile A  502  are received at the SH  516 , which is operatively coupled to an OFI  520 . The OFI  520  in the IOS BSC  505  is operatively coupled to an OFI  522  in the IOS MSC  506  by a trunk. The OFI  522  in the IOS BSC  505  is operatively coupled to a CV  512 , which is operatively coupled to an NPH  528 . 
     The second IOS BSC  507  similarly has a SH  518  and an OFI  524 . The second IOS MSC  508  similarly has an NPH  530 , a CV  514  and an OFI  526 . The NPHs  528 ,  530  are operatively coupled to an IP core  510 . 
     For initial deployment, when VTTS is invoked, all transcoding and echo cancellation in the voice path may be disabled and ISLP supported. For the traditional MSC, a hard handoff will be made from the initial SH to a SH on a PHV6 which supports ISLP for VTTS. MSCs are equipped primarily with PHV7 SHs and a few PHV6 SHs for VTTS support. For the IOS BSC, a non-hard handoff solution may be provided where the initial SH switches to an ISLP mode upon VTTS activation. IOS BSCs may only be equipped with PHV6 SHs. 
     The CVs must also change to a “clear channel” mode where no echo cancellation or gain adjustments are done. The CV cannot be setup initially in clear channel mode as it must support echo cancellation for scenarios where the CV is connected to a TDM network as a result of some feature interaction, such as call transfer, etc. 
     Since the CVs are part of a call independent from the mobile (SH) portion of the call (e.g., isolated by a loop-around trunk or an A2 trunk), no signaling or internal control messaging option is possible for changing the mode of the CV to a clear channel. Two in-band DTMF tones may be used to cause the CV to change to clear channel mode. These may be 2 hard-coded digits from the A-D DTMF range. A two digit combination may be used as a single A through D digit that may be used by certain network nodes or applications, such as voice mail systems. CVs may be modified to recognize this 2 digit pattern and change to a clear channel mode. 
     The following example is a high level VTTS scenario (Traditional MSC). The mobile user pushes the VTTS button. The MSC is notified of the button push via a request utilizing existing functionality. The MMC instructs the PS to allocate the new SH. After a new SH is allocated, the MMC instructs the PS to reconfigure the path using a “Switchpath” message. 
     When the PS gets the “Switchpath” message, the PS uses a Local Switching Demand and Facility Data base system (LDSF) to generate the two DTMF combination in the A-D range, according to one embodiment. After the tone generation, the PS will continue with the “Switchpath” processing and the completion of the hard handoff. 
     The CV may be programmed to recognize the two-digit combination and change from a normal G.711 mode to a clear channel mode, according to another embodiment. 
     The following example is a high level VTTS scenario (IOS BSC). The mobile user pushes the VTTS button. The BSC is notified of the button push via a message, for example a FS_TRANSPORT message, to the SH. Prior to beginning normal VTTS processing, the SH generates the two DTMF digit combination in the A-D range. After the tone generation, the SH will continue with transition to the VTTS mode. 
     The CV in the MSC may be programmed to recognize the two-digit combination and change from a normal G.711 mode to a clear channel mode, according one embodiment. 
     In another embodiment, the circuit trunk loop around may be ISDN User Part (ISU)P. In such an embodiment, the clear channel codec transparently passes frames between the time slot and an RTP stream. 
     The switch or switch module referred to above may be in the packet vocoder. There may be at least four triggers to invoke the packet vocoder&#39;s switch module. For example, in the embodiments depicted in  FIGS. 1 and 2 , triggering may be effected by the MMCs  116 ,  120 ,  216 ,  220 , or by detection of ISLP data by the PV  126 ,  226 . In the FIGS.  4  and  5  embodiments triggering may be effected by DTMF digits sent by the SH  416 ,  516  and detected by the CV  412 ,  512 , or by detection of ISLP data by the CV  412 ,  512 . 
     It is to be understood that although the above-described embodiments refer to clear-channel data that is non-encrypted, the embodiments according to the present method and apparatus may also use clear-channel data that is still in an encrypted format. Such clear-channel data may be encapsulated in G.711 packets and remains unaltered by the clear-channel element. 
     Embodiments of the present method and apparatus have many efficiencies/advantages provided by the packet vocoder/transcoder approach. Embodiments may provide lower latency, and require fewer signal processing resources compared to a system that requires a separate signal processing resource to handle each encoding format as well as an intermediate bearer network to connect the individual signal processing resources. Also, fewer signal-processing resources result in higher channel capacity per unit of hardware, which translates to lower cost per channel. 
     Furthermore, the present packet vocoder/transcoder approach may also be switched dynamically to change its profile so that it switches from its “normal” voice processing profile to its encrypted ISLP+ClearChannel G.711 profile. Dynamic switching of the signal processing profiles is also faster since all four signal processing profiles (EVRC, G711, Encrypted ISLP, and ClearChannel) are managed as one packet vocoder/transcoding channel. 
     Although the depicted embodiments of the present method and apparatus use ISLP over EVRC to G.711/ClearChannel, other encrypted format types may be utilized, such as, HDLC, that are carried over any voice/audio codec packet format (EVRC-B, AMR, GSM-EFR, G.723, G.729ab, G.726, etc.) with the G.711/ClearChannel on the other side. Embodiments may also use un-encryption by the packet vocoder/transcoder and re-encoding into another non-encrypted voice/audio codec format. Also, embodiments may also use un-encryption by the packet vocoder/transcoder and re-encoding into another different encrypted format, and encapsulation as G.711 packets in clear channel mode. 
     The present apparatus in one example may comprise a plurality of components such as one or more of electronic components, hardware components, and computer software components. A number of such components may be combined or divided in the apparatus. 
     The present apparatus in one example may employ one or more computer-readable signal-bearing media. The computer-readable signal-bearing media may store software, firmware and/or assembly language for performing one or more portions of one or more embodiments. The computer-readable signal-bearing medium for the apparatus in one example may comprise one or more of a magnetic, electrical, optical, biological, and atomic data storage medium. For example, the computer-readable signal-bearing medium may comprise floppy disks, magnetic tapes, CD-ROMs, DVD-ROMs, hard disk drives, and electronic memory. In another example, the computer-readable signal-bearing medium may comprise a modulated carrier signal transmitted over a network comprising or coupled with the apparatus, for instance, one or more of a telephone network, a local area network (“LAN”), a wide area network (“WAN”), the Internet, and a wireless network. 
     The steps or operations described herein are just exemplary. There may be many variations to these steps or operations without departing from the spirit of the invention. For instance, the steps may be performed in a differing order, or steps may be added, deleted, or modified. 
     Although exemplary implementations of the invention have been depicted and described in detail herein, it will be apparent to those skilled in the relevant art that various modifications, additions, substitutions, and the like can be made without departing from the spirit of the invention and these are therefore considered to be within the scope of the invention as defined in the following claims.