Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L65/00—Network arrangements, protocols or services for supporting real-time applications in data packet communication
  • H04L65/60—Network streaming of media packets
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L65/00—Network arrangements, protocols or services for supporting real-time applications in data packet communication
  • H04L65/10—Architectures or entities
  • H04L65/102—Gateways
  • H04L65/1023—Media gateways
  • H04L65/103—Media gateways in the network
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
  • H04W88/18—Service support devices; Network management devices
  • H04W88/181—Transcoding devices; Rate adaptation devices

Definitions

• the invention generally relates to the field of transcoding content data in communication networks such as mobile networks. More specifically, the invention relates to a technique of operating a tandem free operation (TFO) control server and a TFO transcoder unit for codec negotiation along a call path.
• TFO tandem free operation
• MMCs Mobile-to-mobile calls
• a speech signal is digitally encoded in the originating mobile user device, sent over a first air interface, transcoded into PCM encoded speech by a first transcoder unit in a fixed network, carried over the fixed network, transcoded again by a second transcoder unit, sent over a second air interface and is finally decoded in the terminating mobile user device.
• More complex call paths extending for example over several PLMNs Public Land Mobile Networks
• PLMNs Public Land Mobile Networks
• PLMNs Public Land Mobile Networks
• Tandem-free operation as defined by the 3GPP (3 rd Generation Partnership Project) in its TS (Technical Specification) 28.062 provides a mechanism that avoids transcoding between two transcoder units in case the speech codecs (the term 'codec 1 refers to a coding-decoding mechanism for performing encoding and decoding on a digital data stream) used upstream and downstream of the two TFO partners are compatible to each other.
• the two transcoder units may for example be included in a TRAU (Transcoding Rate Adaptation Unit) in a GSM network or in a MGW (Media Gateway) in an UMTS network.
• TRAU Transcoding Rate Adaptation Unit
• MGW Media Gateway
• TS 28.062 specifies a TFO protocol for in-band signalling between the two transcoder units within an already established PCM link, e.g. for exchanging the used and/or available codecs.
• TFO will be established between these TFO partners.
• each transcoder unit receives speech frames and forwards them without transcoding to the TFO partner embedded into the PCM stream between the TFO partners.
• TFO starts its signalling after the call path has been established.
• the control plane signalling that controls this call path section is typically a legacy protocol, that cannot transfer codec type or codec list information.
• Out-of-band transcoder control (OoBTC) defined in 3GPP TS 23.153 provides another mechanism that avoids unnecessary transcoding.
• OoBTC Out-of-band transcoder control
• signalling procedures are defined to convey the codec type selected for a call to the affected nodes, i.e. the user device(s) and potential transcoding points in the network.
• Codec negotiation mechanisms are defined to enable the selection of a codec type supported in most or all of the affected nodes. These codec negotiation mechanisms act to resolve codec mismatch situations, thus maximizing the chances of operating in compressed mode end-to-end for, e.g., MMCs.
• a transport-independent call control protocol may be used, for example the BICC (Bearer Independent Call Control) protocol specified in the 3GPP TS 32.205.
• the SDP/SIP protocol as specified by the IEETF provides an Offer/Answer negotiation procedure for codec negotiation, which works essentially similar to OoBTC.
• OoBTC and SDP/SIP work in the call control plane at call setup or during the call, while TFO works on the user plane and only during the established call and only on PCM links.
• OoBTC is used at or after call-setup and attempts to establish a transcoder free connection between mobile devices (or a mobile device and a gateway or edge node of the mobile network). If OoBTC fails to establish a TrFO (Transcoder Free Operation) along a section of the call path, e.g.
• TrFO Transcoder Free Operation
• the in-band TFO mechanism may be used after call setup in that section.
• a call path may include call legs based on transcoding free links (TrFL), and may further comprise call legs based on tandem free links (TFOL) or the default PCM links.
• TrFO transcoding free links
• TFOL tandem free links
• Application of both of the TrFO and the TFO mechanisms may lead to the entire call path being a concatenation of several TFO legs and TrFO legs (and possibly further call legs without any transcoding optimization).
• the selected codecs on each of the TrFO call legs may be locally optimal
• the concatenation of TrFO call legs using different codecs by TFO legs in between may not necessarily be globally optimal.
• Transcoding to PCM may still be required. This may result in a degradation of speech quality, a longer delay in the speech path and higher transcoding costs.
• a method of operating a tandem free operation (TFO) control server comprises the steps of receiving a signalling message comprising a codec list; determining if a dummy codec indicating a codec list transfer action is to be added to the codec list; adding the dummy codec to the codec list depending on the determination; and transmitting the codec list with the dummy codec to a TFO transcoder unit.
• the control server may be part of an MSC (Mobile Switching Center) or a TSC (Transit Switching Center) in a GSM or UMTS network or another node, e.g. in an IMS (IP Multimedia Subsystem) network.
• the TFO transcoder unit may be a TFO partner of a TFO leg, which is controlled by the control server.
• the signalling message may be a control plane signalling message, for example a codec negotiation message according to the BICC or SIP standard.
• a BICC codec negotiation message may for example comprise a list of supported codecs or a list of available codecs, possibly including a selected codec.
• a dummy codec indicating a codec list transfer action may or may not already be included in the signalling message.
• the TFO control server may keep the dummy codec in the codec list, i.e. the server may transmit the codec list unchanged to the TFO transcoder unit.
• the TFO control server may add a dummy codec indicating a desired codec list transfer action to the codec list before transmitting it to the TFO transcoder unit.
• the dummy codec may be (formally) coded as any other codec in the codec list. It may be identifiable as a dummy codec by specifying the codec identity (or similar fields of the codec specification) as a new codec. As another example, the dummy codec may be indicated as a proprietary codec , which is specifically used for the purpose of conveying information related to the codec list transfer.
• the signalling message may relate to an OoBTC operation to, e.g., achieve or optimize a TrFO.
• the signalling message may relate to an OoBTC operation according to SDP/SIP or IMS.
• the message may be a BICC codec (re-)negotiation message.
• the signalling message may be a SIP message, e.g. a SIP Invite or SIP Response message, which may contain codec lists.
• the codec list including the dummy codec may be transmitted to the TFO transcoder unit as a TFO control message.
• a "MOD.req"-message according to the H.248 standard may be used for providing the codec lists to the transcoder unit, which may be a MGW or a TRAU.
• the dummy codec may indicate at least one of a request for transferring the codec list, a request for reception of a codec list from a remote TFO partner, and an acknowledgement relating to a reception of a codec list, which may for example have been received from a remote or distant TFO partner (instead of "remote TFO partner", in the TS 28.062 frequently the term "distant TFO partner" is used. Both adjectives 'remote' and 'distant' are used synonymously herein).
• the dummy codec may comprise indicator bits which represent the indicated information. The indicated information may coincide with the indicated information carried by the received OoBTC and/or SIP signalling message.
• the codec list may comprise at least one of supported codecs, available codecs, and a selected codec.
• the dummy codec may for example comprise a pointer indicating the selected codec in the codec list.
• the first codec in the TFO codec list may be a selected codec whereas the further codec list may represent a list of available codecs.
• the supported codec list may comprise a list of codecs prospectively supported by the nodes along the call path.
• the supported codec list may be sent, e.g., from a call control node originating an OoBTC operation.
• the available codec list may be a subset of the supported codec list indicating the actually available codecs along the (section of the) call path and may be returned in a backward signalling to the OoBTC originating control node.
• the dummy codec may have been extracted from an OoBTC message in the control plane comprising a codec lists or from an SDP/SIP Messages comprising a codec list.
• a further method of operating a TFO control server comprises the steps of receiving a codec list from a TFO transcoder unit, wherein the codec list includes a dummy codec indicating a codec list transfer action; determining the dummy codec in the codec list; and handling the codec list based on the indicated codec list transfer action.
• the TFO transcoder unit may be a TFO partner of a TFO leg.
• the TFO transcoder unit may have received the codec list, e.g. in a Con_Req configuration frame (a "Generic Configuration Frame") according to TS 28.062, from the other TFO partner of the TFO leg.
• the handling may comprise the further step of transmitting a signalling message including the codec list to a remote control server along the call path.
• the signalling message may for example be a BICC codec negotiation message including the received codec list with or without the dummy codec.
• the handling may additionally or alternatively comprise an OoBTC operation, e.g. according to TS 23.153.
• BICC or SDP/SIP related functionality may be included, e.g. the preparation and transmission of a BICC / SIP signalling message.
• the control server may remove codecs from the received codec list in case these codecs are not supported in the local network.
• the control server may also indicate e.g. a selected codec to the TFO transcoder unit.
• the handling may comprise the further step of forwarding the codec list as at least one of a supported codec list, an available codec list and a codec list indicating a selected codec, e.g. in an OoBTC signalling message, for example a BICC or SIP message.
• the handling may comprise the further step of removing the dummy codec and/or unsupported codecs from the codec list.
• a method of operating a TFO transcoder unit comprises the steps of receiving a codec list, wherein the codec list includes a dummy codec indicating a codec list transfer action; determining the dummy codec in the codec list; forwarding, based on the indicated codec list transfer action, the received codec list including the dummy codec.
• the TFO transcoder unit may be a TRAU or part of a MGW.
• the method comprises the step of receiving the codec list from a TFO control server, for example an MSC or TSC.
• the codec list may be sent "vertically downward" from a TFO control server to the TFO transcoder unit, which may then "horizontally" forward the codec list including the dummy codec towards a distant TFO Partner.
• the codec list may be received in a TFO control message.
• the method may further comprise the step of forwarding the received codec list including the dummy codec in a TFO configuration frame to a remote TFO partner.
• the codec list may be forwarded in a signalling message according to the TFO in-band signalling mechanism.
• the received codec list may be forwarded in a TFO_RE0__L message to a distant TFO partner, wherein the TFO_REQ_L message comprises a specific TFO extension block, which includes the transfer actions indicated by the dummy codec.
• the codec list transfer action may be performed during a TFO mismatch state or any other TFO state.
• the codec list may be forwarded in a configuration frame although TFO is not in state OPERATION between the TFO partners.
• the codec list transfer action may also be performed when TFO is in state OPERATION.
• the codec may alternatively be received from a remote TFO partner, i.e. a remote transcoder unit incorporated for example into a TRAU or a media gateway.
• a remote TFO partner i.e. a remote transcoder unit incorporated for example into a TRAU or a media gateway.
• the codec list may be received "horizontally" from the remote TFO partner and may then be sent "vertically upwards" from the TFO transcoder unit to a TFO control server.
• the codec list including the dummy codec may be received in a TFO configuration frame from a distant TFO partner.
• the codec list may be received in a TFO_REQ_L message from a distant TFO partner, wherein a specific TFO Extension block is appended to the TFO_REQ_I_ message including the transfer actions indicated by the dummy codec.
• the codec list may be received in an TFO state, for example in a TFO Mismatch state or a TFO Operation state.
• the method may then further comprise the step of forwarding, based on the determined codec list transfer action, the received codec list including the dummy codec to a TFO control server. For example, a notification message "NOTIFY. REQ" according to H.248 may be used.
• a computer program product which comprises program code portions for performing the steps of any one of the method aspects discussed herein when the computer program product is executed on one or more computing devices, for example a control server or a transcoder unit.
• the computer program product may be stored on a computer readable recording medium, e.g. a CD-ROM or DVD.
• a TFO control server comprises a first interface component adapted for receiving a signalling message comprising a codec list; a codec list transfer component adapted for determining if a dummy codec indicating a codec list transfer action is to be added to the codec list and adapetd for adding the dummy codec to the codec list depending on the determination; and a second interface component adapted for transmitting the codec list with the dummy codec to a TFO transcoder unit.
• a TFO control server which comprises a first interface component adapted for receiving a codec list from a TFO transcoder unit, wherein the codec includes a dummy codec indicating a codec list transfer action; a determination component adapted for determining the dummy codec in the codec list; and a codec list handling component adapted for handling the codec list based on the indicated codec list transfer action.
• a TFO transcoder unit which comprises a first interface component adapted for receiving a codec list, wherein the codec list includes a dummy codec indicating a codec list transfer action; a determination component adapted for determining the dummy codec in the codec list; and a second interface component adapted for forwarding, based on the indicated codec list transfer action, the received codec list including the dummy codec.
• Fig. 1 is a schematic illustration of a call path in an ongoing MMC
• Fig. 2 is a functional block diagram schematically illustrating embodiments of server nodes and transcoder units
• Fig. 3 is a flow diagram illustrating steps of a first method embodiment of operating a TFO control server
• Fig. 4 is a flow diagram illustrating steps of a second method embodiment of operating a TFO control server
• Fig. 5 is a flow diagram illustrating steps of a method embodiment of operating a TFO transcoder unit
• Fig. 6 is a sequence diagram schematically illustrating a message flow for codec list transfer via a TFO leg
• Fig. 7 is a schematic illustration of an embodiment of a dummy codec for indicating a codec list transfer action.
• 'interface 1 or 'interface component 1 as used herein may denote a 'functional interface', i.e. a sub-structure contained within a functional component or higher- level structure (e.g., a hardware and/or software component or functional entity) specifically designed for performing communications with further, external components or structures.
• a functional interface may typically, but not exclusively, be implemented as software.
• FIG. 1 schematically illustrates a complex call path 100 for an ongoing MMC between mobile user devices 102 and 104.
• Speech data is forwarded for example from user device 102 via access network RANl, multiple media gateways MGWl - MGW6 and access network RAN2 towards second user device 104, and vice versa.
• each MGW incorporates a transcoder unit.
• the MGWs are controlled by multiple MSCs (MSCl, MSC2) and TSCs (TSCl - TSC4).
• the speech data is conveyed between user devices 102 and 104 without any transcoding.
• the data is forwarded via TrFO in several call legs and is forwarded via TFO in other call legs.
• out-of-band transcoder control is performed via BICC between the server nodes along the TrFO call legs
• no control plane signalling regarding codec negotiation is performed via the ISUP signalling connections between server nodes along the TFO call legs.
• codec lists are forwarded via the TFO call leg between the TFO partners MGW2 and 3, as well as the TFO partners MGW4 and MGW5. This will be described in more detail in the following.
• Fig. 2 illustrates a TFO call leg 200 extending between transcoder units 202 and 204. These are controlled by TFO control server nodes 206 and 208, respectively.
• the TFO call leg 200 may be an implementation of the call leg extending between MGW2 and MGW3 or MGW4 and MGW5 in Fig. 1.
• the transcoder units 202 and 204 may then be part of an MGW each (not shown in Fig. 2).
• the TFO control server 206 comprises a first interface component 210, a codec list transfer component 212 and a second interface component 214.
• the interface component 210 is adapted for receiving a signalling message comprising a codec list.
• the codec list transfer component 212 is adapted for determining if a dummy codec indicating a codec list transfer action is to be added to the codec list. Further, the codec list transfer component is adapted for adding the dummy codec to the codec list depending on the determination.
• the interface component 214 is adapted for transmitting the codec list with the dummy codec to the TFO transcoder unit 202.
• the transcoder unit 202 comprises a first interface component 216, a determination component 218, a second interface component 220.
• the interface component 216 is adapted for receiving a codec list from the control server 206, wherein the codec list includes a dummy codec indicating a codec list transfer action.
• the determination component 218 is adapted for determining the dummy codec and the indicated codec list transfer action in the received codec list. In case the codec list transfer action indicates a forwarding of the received codec list, the determination component 218 provides the received codec list to the second interface component 220, which is adapted for forwarding, based on the indicated codec list transfer action, the received codec list including the dummy codec to the TFO partner 204.
• the interface component 220 may further receive speech data for transfer in TFO frames to the TFO partner 204 from other components of the MGW (not shown) in which the transcoder unit 202 is incorporated.
• a component may for example be an interface adapted for receiving speech data in a TrFO call leg.
• the transcoder unit 204 comprises the first interface component 222, a determination component 224 and a second interface component 226.
• the interface component 222 is adapted for receiving a TFO codec list.
• the codec list includes a dummy codec indicating a codec list transfer action from the TFO partner, namely the TFO transcoder unit 202.
• the determination component 224 is adapted for determining the dummy codec and the indicated codec list transfer action in the received codec list.
• the received codec list is forwarded to the interface component 226, which is adapted for forwarding, based on the indicated codec list transfer action, the received codec list including the dummy codec to the associated TFO control server 208.
• the interface component 222 is also adapted for forwarding received TFO frames, which may include speech frames, towards other components of the MGW (not shown) hosting the transcoder unit 204.
• Such a component may for example be an interface component for transmitting the received speech frames further along the call path in a TrFO call leg.
• the TFO control server 208 comprises a first interface component 228, a determination component 230 and a codec list handling component 232.
• the interface component 228 is adapted for receiving a codec list from the transcoder unit 204.
• the codec list includes a dummy codec indicating a codec list transfer action.
• the determination component 230 is adapted for determining the dummy codec in the received codec list, and further for determining the indicated codec list transfer action.
• the determined codec list transfer action is provided to the codec list handling component 232, which is adapted for handling the codec list based on the indicated codec list transfer action.
• the component 232 may comprise for example an interface subcomponent for forwarding the received codec list with or without the dummy codec via a signalling (BICC) connection to a remote control server (not shown).
• the component 232 may further comprise subcomponents for removing from the received codec list codecs, which are not supported at the downstream call leg.
• FIG 3 is a flow diagram illustrating an embodiment 300 of a method of operating a TFO control server.
• the control server may be an embodiment of one of the call control nodes TSCl - TSC4 in Fig. 1 or of the control server 206 in Fig. 2.
• the procedure 300 is triggered in step 302 by receiving a signalling message comprising a codec list.
• the signalling message may be received by interface 210 of the TFO control server 206 in the control plane in Fig. 2.
• the signalling message may be received by interface 210 of the TFO control server 206 in the control plane in Fig. 2.
• step 304 it is determined if a dummy codec is to be added to the received codec list.
• the dummy codec indicates a codec list transfer action.
• step 306 the dummy codec is added to the codec list depending on the determination.
• step 308 the codec list with the dummy codec is transmitted to a TFO transcoder unit. The procedure ends in step 310 with the TFO control server being idle and waiting for further signalling messages to arrive.
• Figure 4 illustrates steps of an embodiment 400 of another method of operating a TFO control server.
• the procedure starts in step 402 by the reception of a codec list from a TFO transcoder unit.
• the codec list includes a dummy codec indicating a codec list transfer action.
• the dummy codec in the codec list is determined.
• the indicated codec list transfer action may be determined.
• the codec list is handled.
• step 406 may comprise transmitting a signalling message including the codec list to a remote control server via interface 232 in Fig. 2.
• the method ends in step 408 with the control server being idle and waiting for further codec lists to be received from the TFO transcoder unit.
• FIG. 5 is a flow chart illustrating steps of an embodiment 500 of a method of operating a TFO transcoder unit.
• the procedure starts in step 502 with a reception of a codec list, e.g. via interface 216 or interface 222 in Fig. 2.
• the codec list includes a dummy codec indicating a codec list transfer action.
• the dummy codec in the codec list is determined.
• the received codec list including the dummy codec is forwarded based on the indicated codec list transfer action, e.g. on interface 220 or 226.
• the method ends in step 508, in which the transcoder unit is idle and waits for further incoming messages/configuration frames.
• Figure 6 is a sequence diagram illustrating an embodiment of a sequence 600 of messages and frames exchanged between a TFO control server 602, MGWs 604 and 606, and a further TFO control server 608.
• Nodes 602 - 608 may be implementations of the nodes 208, 204, 202, 206 of Fig. 2.
• the MGWs 604 and 606 include transcoding units.
• the control server 608 receives an OoBTC request for mid-call codec negotiation from a remote control server (not shown) in the call path.
• the codec negotiation is based on a BICC signalling message, which includes a supported codec list (SCL).
• SCL supported codec list
• the received signalling message may already include a dummy codec, such that the codec list transfer component may determine that no dummy codec needs to be added to the codec list and that the codec list is to be forwarded including the received dummy codec.
• the codec list transfer component may or may not change a code list transfer action indicator associated with the dummy codec.
• Figure 7 illustrates an example embodiment 700 of a dummy codec, which may added by the control server 608 to the received codec list in Fig. 6 or which might be included already in the received codec list.
• the dummy codec 700 is coded in a similar way as other codecs, see 3GPP TS 26.103.
• the codec identity (CoID) and the organization identity (OID) identify the codec as a proprietary codec.
• only one of the CoID and the OID may be used to indicate the dummy codec.
• a particular value of, e.g., the CoID may be standardized to indicate a dummy codec which is specifically used for the purpose of codec list transfer.
• the dummy codec may be appended at the end of the codec list. In other embodiments, the dummy codec may be included at another position in the codec list.
• a dummy codec such as the codec 700 allows the transport of signalling information across a TFO leg or any other signalling leg.
• the dummy codec 700 includes a two-bit codec list transfer action indicator.
• the dummy codec may further include a pointer pointing towards a selected codec (SC) in an available codec list (ACL).
• SC selected codec
• ACL available codec list
• a codec at a particular position in the codec list e.g. the first codec, is a selected codec.
• the codec list transfer component in server 608 has set the codec list transfer action indicator to "01" indicating a codec list "transfer request", i.e the TFO codec list shall be sent all the way to the distant control server and then further on.
• a TFO control message MOD.req with the SCL including the appended dummy codec is sent to the MGW 606.
• the MGW 606 (more precisely, its determination component 218) determines that a dummy codec is included in the received codec list and further determines OID and CoID of the dummy codec.
• the determination component further determines the Codec List Transfer Action Indicator.
• the determination component In response to the determined list transfer action "transfer request", the determination component provides the received codec list including the dummy codec to the interface component 220 of the MGW 606.
• a TFO generic configuration frame with CON_REQ is constructed, which includes the received codec list (i.e. the SCL from the OoBTC codec negotiation) with the dummy codec and the unchanged action indicator.
• the Con_Req is sent to the TFO partner, the MGW 604.
• the Con_Req is received at the MGW 604.
• the determination component 224 of MGW 604 checks the received TFO codec list and determines the dummy codec as well as the action indicator.
• the interface component 226 of MGW 604 forwards the received SCL in a notification message to the server 602. No determination of an optimal codec may be performed in the MGW 604.
• the MGW 604 acknowledges reception of the codec list by sending a configuration frame "Con_Ack", in which the action indicator is set to "no indication", back to the MGW 606 (due to this indication, the MGW 606 does not send a notification message indicating the codec list received with the Con_Ack to the server 608).
• a Con_Ack may never trigger a forwarding of an included codec list, irrespective of any indication provided by the dummy codec.
• the control server 602 receives the notification with the TFO codec list, which is ultimately the SCL received by the server 608 plus the dummy codec.
• the codec list handling component 232 of the control server 602 triggers a BICC mid-call codec negotiation procedure, in which the received codec list is used as an SCL.
• the component 232 removes codecs that are not supported by the network the server 602 is located in.
• the server 602 thus handles the received codec list as if it would have been received via OoBTC from the server 608.
• the component 232 eventually removes the dummy codec from the codec list, such that only the original SCL is forwarded in the BICC codec negotiation message.
• the dummy codec may be included in the forwarded codec list.
• TFO may be in state MISMATCH.
• an SCL may be forwarded via a TFO leg between TFO partners, for example by using a TFO in-band signalling message.
• the dummy codec may be added as a TFO extension block at the end of the TFO message, cf. TS 28.062.
• an available codec list (ACL) with or without a selected codec (SC) may be passed as a TFO codec list including a dummy codec along a TFO call leg.
• the action indicator may indicate a "transfer request" in these cases also.
• a possibly included SC may be indicated by a pointer included in the dummy codec, which points to the selected codec in the codec list (see Fig. 7).
• the SC may be dropped by a control server receiving the codec negotiation signalling message. Only the ACL may be forwarded along the TFO leg.
• An action indication "successful transfer” may be used to acknowledge the reception of a codec list.
• this indicator may be used to pass the "Successful Modification" indication of a BICC mid-call negotiation procedure along a TFO call leg.
• the action indicator "transfer needed” may be used to pass a request for reception of a codec list along a TFO leg. This indication may further be used for failure messages, e.g. regarding a mid-call negation failure or codec modification failure.
• the technique proposed herein allows the transfer of codec lists along TFO legs of a call path.
• an original codec list received on the control plane by a first control node is "tunnelled" through the TFO link to a second control node.
• the result may be identical to the direct transfer of the codec list by control plane signalling between the two control nodes.
• BICC SCLs and ACLs with or without SC may be transferred along TFO legs.
• a codec list along at least a part of a call path which is a concatenation of TFO legs and TrFO (see TS 23.153) legs. This permits to find the globally best codec or codec combination for this call path.
• the technique proposed herein allows the transfer of the BICC successful modification indication.
• the technique also allows to request a codec list and can easily be implemented, as the TFO state machine may remain unchanged.
• a dummy codec which is identified as a new codec may be dropped by a TFO handler in a transcoder unit or control server which does not support the methods according to the technique. Therefore, the technique is backward compatible.
• the dummy codec may be added to any codec list which passes by at least one of the Nc-, Mc- and Nb-interfaces (see TS 23.002).
• the mechanism of providing a codec list transfer action indicator as an N-bit indicator allows the straightforward definition of further action indications, if desired.
• the dummy codec described herein may also be used to collect various information elements (IEs), new or existing ones, in an easy to implement and backward compatible way.
• IEs information elements
• a codec list transfer action as described herein may also be transported with a new information element.
• such an IE may optionally be included in messages transferred via the relevant interfaces.
• the IE may be included in in-band signalling messages and/or configuration frames exchanged between the TFO partners, and/or OoBTC/BICC or SIP/SDP signalling messages.

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• 2007
  • 2007-01-18 WO PCT/EP2007/000426 patent/WO2008086824A1/en active Application Filing

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