WO2009000292A1

WO2009000292A1 - Technique for reducing transcoding operations in a telecommunication system

Info

Publication number: WO2009000292A1
Application number: PCT/EP2007/005589
Authority: WO
Inventors: Karl Hellwig; Dirk Kampmann
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2007-06-25
Filing date: 2007-06-25
Publication date: 2008-12-31

Abstract

The invention relates to a technique for controlling a communication over a telecommunication system (200), the communication comprising a transfer of content frames, e.g. speech frames, between a frame adaptation unit (FRAU 208) in a radio network of the system and a media gateway (MGW 206) in a core network of the system without transcoding of the content frames between the FRAU (208) and the MGW (206) and without codec negotiation between the FRAU (208) and the MGW (206). A method embodiment for performing the technique in the FRAU comprises receiving signalling (212) related to the communication from an MSC (202), receiving content frames from within the radio network (Ater), adapting the content frames, based on the received signalling, to a radio/core network interface (210, e.g. a TFO interface); and sending the adapted content frames to the MGW (206).

Description

Technique for reducing transcoding operations in a telecommunication system

Technical Field

The present invention relates to telecommunication systems, and in particular to a technique for controlling a communication which comprises a transfer of content frames, e.g. speech frames, between a radio network and a core network of the telecommunication system.

Background

Mobile telecommunication systems like GSM, GPRS and UMTS become more and more popular for the transmission of content such as speech, but also other data such as facsimile, SMS, image and video data. Mobile systems even dominate traditional fixed networks like POTS (Plain Old Telephone Service), ISDN (Integrated Services Digital Network) etc. in certain parts of the world. This trend will prospec- tively also hold for future mobile networks such as SAE/LTE (System Architecture Evolution / Long Term Evolution) networks currently developed by the 3GPP (3^rd Generation Partnership Project).

Fig. 1 schematically illustrates a mobile communication system 160 comprising a typical GERAN (GSM Edge Radio Access Network) radio network 170 and an MSS-CN (Mobile Soft-Switch Core Network) 180. As shown, radio network 170 and core network 180 each comprise a plurality of nodes 105 - 125 and 130 - 145, respectively, that are involved when performing a communication such as a speech call between mobile stations MSl 100 and MS2 150. For the sake of completeness it should be noted that not all nodes of a mobile communication system are depicted in Figure 1 and the following figures.

The mobile station 100 is connected over a radio link to a base transceiver station (BTS) 105. As the available bandwidth over the radio interface is generally limited, speech signals are transported in compressed form on the radio interface. A compression codec is utilized within the MS 100 to compress (encode) a microphone signal for uplink transmission (i.e. towards the communication network). Vice versa, in the MS 150 at the other end point of the communication, a received compressed speech signal has to be decompressed (decoded) in a downlink direction (i.e. from the communication network to the MS), before sending it to a loud speaker.

Various codec types exist for radio networks. For a GERAN, such as the network 170 in Fig. 1, the available codecs may comprise HR (Half Rate), FR (Full Rate), EFR

(Enhanced FR), AMR (Adaptive Multi-Rate codec), AMR-WB (AMR-Wide Band). These codecs differ in their respective bandwidth requirements, however, generally require less bandwidth than a standard PCM signal of 64 kilobits per second (kbps). As an example from the AMR codec family, the FR-AMR and HR-AMR codecs requires a traffic channel with a maximum data rate of 12.2 kbps and 7.4 kbps, respectively; AMR-WB also requires a Full Rate traffic channel with a maximum net bit rate of 12.65 kbps.

Referring further to Fig. 1, the speech signal received from the MS 100 over the radio interface is still transmitted within the GERAN 170, i.e. over the Abis- and the Ater- interfaces, in compressed form for efficient resource usage. As depicted in Fig. 1, the Abis interface is defined between BTS 105 and a. group switch (GS) 110, and the Ater interface is defined between the GS 110 and a transcoding and rate adaptation unit (TRAU 115) near the edge of the GERAN 170. It is to be noted that the configuration with the GS 110 being a stand-alone entity in the radio network 170 is optional. Alternatively, a component corresponding to the GS 110 may be provided, e.g., inside the BSC 125. The TRAU 115 transcodes the compressed speech signal on the Ater-interface to a PCM signal on the A-interface. In the other (downlink) direction, the TRAU 115 compresses a PCM signal received over the A-interface, such that the MS 100 has to decompress the downlink signal by a corresponding decoder.

The radio network 170 is shown as further comprising a Handover-Handler (HoH) 120 inserted in the call path between the TRAU 115 and the MGW 140. The HoH 120 handles BSC-internal handover (HOV) scenarios. It is to be noted, however, that the HoH 120 is optional, i.e. its functionality could be placed also at a different position either as a stand-alone entity or in conjunction with other functions.

In principle, communication signals shall be transported as PCM signals within the radio network 170 and the core network 180, and over the Nb-interfaces in the core network 180. However, as PCM is not bandwidth-efficient, a different codec may be selected for use within the core network 180, e.g. between the MGWs 140, 145. Several mechanisms exist to achieve this. For example, the MSCs 130, 135 along the call path may negotiate the codec to be used. The negotiation process comprises that the involved MSCs 130, 135 agree on a common codec to be used along the call path (such that transcoding might be avoided).

An example for such a negotiation process is the OoBTC (Out-of-Band-Transcoder- Control) mechanism specified in the 3GPP TS (Technical Specification) 23.153, also called TrFO (Transcoder Free Operation) from a transport plane point of view. After successful negotiation, which is performed before the first speech frames are transported, the MSCs 130, 135 force their associated media gateways 140, 145 to use the negotiated codec on the Nb-interface. Via the A-interface, the appropriate MSC may only suggest a list of codecs sorted by order of preference to be used to the BSC. For example, in Fig. 1 the MSC 130 in the core network 180 may signal to the BSC 125 in the radio network 170 the preferred codec to be used for the call. The BSC 125 may then instruct the MS 100, the BTS 105 and TRAU 115 accordingly. However, the BSC 125 is free to follow such a suggestion or to employ another codec of the list, e.g. due to limited resources or overload situation at the served radio interface. For these and other reasons, OoBTC does not extend over the A-interface. Another known technique to reduce the number of transcoding procedures along the call path is a mechanism called Tandem-Free Operation (TFO). This is an in-band- signalling mechanism, which is basically performed between two transcoding units, and which may for example be performed between TRAU 115 and MGW 140 in Fig. 1, i.e. over the A-interface. This TFO codec negotiation mechanism may only be performed after a PCM link already has been established (i.e. after call setup). The TFO partners may only use a small number of bits in the PCM bitstream for exchange of negotiation messages to avoid audible distortions. This kind of in-band signalling is slow, i.e. a common codec may be installed (if at all) only some several seconds after the subscribers of MSl 100 and MS2 150 have started already to speak.

In case the TFO negotiation is successful, i.e. a common available codec is found, compressed speech according to the negotiated codec may be tunnelled via the PCM channel. As a basic "common codec" and as a fallback possibility, the standard PCM G.711 signal has to be available anyway and all the time. Therefore, even in case TFO can be established over the A-interface, transcoding of the compressed signal into the PCM signal is still required in the TRAU and MGW, although this signal might not be used at all. Therefore each TRAU, such as the TRAU 115 of Fig. 1, requires a transcoding functionality for transcoding a compressed speech signal into at least one of a PCM signal and another codec for the uplink direction, and requires a corresponding functionality for the downlink direction. Further, a TRAU comprises a frame adaptation facility for adapting speech frames, which typically include control information, from a frame format (¹TRAU format") required for the Ater interface to a frame format as required over the A-interface. Some other functionalities might also be harboured in the TRAU. Typically, however, the transcoding consumes by far the largest fraction of the available processing resources in the TRAU.

Summary

It is an object of the invention to provide a technique for reducing the number of transcoding operations in a telecommunication system comprising a radio network and a core network.

According to a first aspect of the invention, a method of controlling a communication over a telecommunication system is proposed. The communication comprises a transfer of content frames including compressed content between a frame adaptation unit (FRAU) in a radio network of the telecommunication system and a media gateway (MGW) in a core network of the telecommunication system without transcoding of the content frames between the FRAU and the MGW and without codec negotiation between the FRAU and the MGW. The method comprises, at the FRAU, the steps of receiving, from a master node associated with at least one of the FRAU and the MGW, signalling related to the communication; receiving content frames of the communication from within the radio network; adapting the received content frames, based on the received signalling, to an interface between the radio network and the core network; and sending the adapted content frames to the MGW.

In one scenario, the FRAU and the MGW are interconnected via an A interface of a GSM or UMTS network. The radio network may, e.g., be a 2G (GSM) radio network or a GERAN in, for instance, a 2.5G or 3G (UMTS) network. The media gateway may be any transport node in a core network, e.g., on a user plane, or may comprise a similar transport functionality inside another core network node such as an MSC. The content may comprise speech or other compressed data. The communication may be a speech call or any other connection-oriented or connectionless data communication. The FRAU may be a stand-alone node or may be implemented in another node such as, e.g. in a TRAU of the radio network. The interface between the radio network and the core network may be an A-interface of a GSM or UMTS mobile network. A particular representation of such an A-interface may be a TFO interface, i.e. the content frames may be exchanged between FRAU and MGW in a format as required by a TFO standard, e.g. the TFO standard specified in the TS 28.062.

The signalling received from the master node may comprise an indication of the requested frame adaptation. For example, the signalling may comprise an indication of a codec used in an uplink direction of the communication in the radio network, Alternatively, the signalling may only comprise an indication of a codec type or a predefined set of codecs. For example, the signalling may indicate a set of AMR codecs.

The aspect that frame handling in the FRAU is performed without transcoding of the content frames may also exclude, e.g., the generation of a PCM signal from the received content frames. I.e., even if the adapted content frames are sent to the MGW in a PCM link, for instance using few of the least significant PCM bits only, there will be no PCM signal on the remaining most significant bits provided to the MGW.

In one representation of the invention, a codec information related to a codec to be used for the communication is transmitted from a communication control node in the core network to a base station controller in the radio network. For example, an MSC in the core network may in a first step determine the codec to be used in the radio network and in a second step send an indication of this codec to the BSC. The de- termination of the codec in the first step may or may not comprise a codec negotiation phase between MSC and BSC. The FRAU may receive the codec information from the master node via the BSC.

A codec negotiation may be performed between the communication control node in the core network and the base station controller in the radio network.In this case, the codec information transmitted from the communication control node to the base station controller may be the last step in the codec negotiation. The signalling received by the FRAU may then relate to the negotiated codec. For example, according to one implementation of the invention, a codec for the (uplink) communication may be negotiated between a communication control node in the core network, such as an MSC, and a base station controller in the radio network, such as a BSC. The codec negotiation may include that the base station controller in the radio network pro- poses one or more codecs, which then the communication control node in the core network may use for deciding on the codec to be used for the communication. In any case, the base station controller and the communication control node may eventually have to agree on a codec to be used.

In some implementations of the invention, the BSC may always follow the proposal of the MSC without a prior negotiation phase, for example because the BSC is configured in that way or because it is in another way assured that sufficient resources are available over the radio interface. As an example, the BSC may be configured to follow the proposal of the MSC for a predefined set of codecs, e.g. if the proposed codec is one of an AMR-WB codec. At least in this case, it is essentially the MSC which controls the frame adaptation operation in the FRAU.

Not only in the cases where a codec negotiation is performed between MSC and BSC (i.e. in the control plane), but also in the cases where the BSC is configured to follow the instruction from the MSC without a prior codec negotiation phase between MSC and BSC, a codec negotiation between FRAU and MGW, e.g. a TFO negotiation (i.e. in the user plane), may not be required. For instance, the codec negotiation performed in the control plane may be used to ensure that the same or a compatible codec is used between the FRAU and the MGW.

The master node may be either one of the communication control node or the base station controller. For example, the master node may be an MSC, e.g. an MSC serving an endpoint of the communication (such as a mobile station accessing at the radio network), or the master node may alternatively be a BSC in the radio network controlling the FRAU. The signalling from the master node to the FRAU may relate to the codec indicated in the codec information transmitted from the communication control node to the base station controller. Additionally or alternatively, the signalling may comprise a trigger indicative of a predefined resource allocation in the FRAU. For instance, in case a network design ensures that the FRAU is only inserted into the call path (for example, instead of a TRAU) in case a particular codec or codec type or one of a set of codecs is used, the frame adaptation behaviour of the FRAU may fixedly implemented therein, such that a simple trigger signal is sufficient to activate the FRAU. The trigger may further comprise an indication related to a resource allocation. In case the signalling comprises only a trigger signal for the purpose of resource allocation in the FRAU, the method may comprise the further step of preparing codec information indicative for the used codec or codec type in response to the receipt of the signalling. For example, preconfigured codec information may be accessed and activated to be applied to incoming content frames. Such preconfigured codec information may be stored in association with the FRAU.

According to one variant of the invention, each content frame comprises control information specific for the radio network in addition to the content. The adaptation of the content frames may then comprise to change the radio network specific control information to core network specific control information. The signalling received from the master node may relate to the differences between the radio network specific control information and the core network specific control information. For example, the signalling may indicate a predefined mapping table for mapping control bits representing the radio network specific control information onto control bits representing the core network specific control information. In one implementation of the invention, the FRAU adapts frames received from the radio network as TRAU frames to a TFO frame format. Thus, the content frames may be TRAU frames received in the FRAU over an Ater interface of a GERAN and sent as TFO frames via an A inter- face towards a the MGW in a core network.

One mode of the invention comprises the further steps of generating a data stream comprising the adapted content frames, and sending the data stream to the MGW. For example, the data stream may be transported in a PCM link. The adapted com- pressed content frames may be sent in one or more least significant bits. No PCM signal may be provided in the most significant bits of the PCM link. The upper bits of the PCM link may not be configured in any way or may be set to one of an undefined value or a predefined constant value. Additionally or alternatively, one or more other compressed content streams may be transported in the upper bits of the PCM link.

The method may comprise the step of sending, upon receipt of the signalling, a message indicative of the signalling to the MGW. This message may, for example, be a Generic Configuration Frame according to the TS 28.062 and may indicate the codec used in the radio network. In another variant, the message may simply trigger the MGW to prepare for the reception of content frames from the FRAU. In case the FRAU and the MGW are statically assigned to each other, apart from such a trigger message, no further information may be required for appropriate frame handling. The signalling from the master node may be received in a set-up phase of the communication; e.g. during setup of a speech call. Additionally or alternatively, the signalling may be received in a codec changing phase during the ongoing communication, e.g. during a handover.

According to a second aspect of the invention, another method of controlling a communication over a telecommunication system is proposed, in which the communication comprises a transfer of content frames including compressed content be- tween a media gateway (MGW) in a core network of the telecommunication system and a frame adaptation unit (FRAU) in a radio network of the telecommunication system without transcoding of the content frames between the MGW and the FRAU and without codec negotiation between the MGW and the FRAU. The method comprises, at the FRAU, the steps of receiving, from a master node associated with at least one of the FRAU and the MGW, signalling related to the communication; receiving content frames of the communication from the MGW; adapting the received content frames, based on the received signalling, to a radio network interface; and sending the adapted content frames into the radio network.

Whereas the first aspect of the invention relates to an uplink direction of the communication, the second aspect relates to a downlink direction. The modes, implementations and variants summarized above for the first aspect of the invention therefore apply analogously also to the second aspect. For example, the signalling received from the master node may be the identical signalling for the first and the second aspect. The radio network interface may, e.g., be an Ater interface in a GERAN. A codec used in the radio network and/or the core network in the uplink direction may or may not be identical to a codec used in the downlink direction.

According to a third aspect of the invention, a method of controlling a communication in a FRAU is proposed, in which the communication comprises a transfer of content frames in uplink direction and in downlink direction, the method comprising the steps of the first and the second aspect of the invention.

According to a fourth aspect of the invention, a further method of controlling a com- munication over a telecommunication system is proposed, in which the communication comprises a transfer of content frames including compressed content between a frame adaptation unit (FRAU) in a radio network of the telecommunication system and a media gateway (MGW) in a core network of the telecommunication system without transcoding of the content frames between the FRAU and the MGW and without codec negotiation between the FRAU and the MGW. The method comprises, at the MGW, the steps of receiving, from a master node associated with at least one of the FRAU and the MGW, signalling related to the communication; receiving content frames from the FRAU; converting the received content frames, based on the received signalling, according to a conversion mode; and sending the converted content frames towards a destination of the communication.

Whereas the first and second aspects of the invention relate to the FRAU, the third aspect relates to the MGW. Insofar applicable, the modes, implementations and variants summarized above for the first and second aspect of the invention may apply analogously to the third aspect. For example, the MGW, which may be a standalone entity or integrated into an MSC or any other communication control node, may be interfacing with the FRAU via an A interface of a GSM or UMTS network. The signalling from the master node, e.g. an MSC controlling the MGW, may be received in a set-up phase of the communication or in a codec changing phase during the ongoing communication.

In one implementation of this aspect of the invention, the signalling is received via the FRAU. For example, the signalling may comprise an indication of a codec or codec type used in the radio network and may be conveyed to the MGW from an MSC via a BSC controlling the FRAU, and the FRAU. For instance, the signalling may arrive at the MGW in a Generic Configuration Frame over a TFO interface.

The signalling may comprise an indication of the conversion mode. This may, for example, include an indication of the FRAU; the handling in the MGW may be configured in a static way for content frames received from a particular FRAU. The indication may simply be a network address of the FRAU.

Additionally or alternatively, the signalling may comprise an indication of one or both of a type of the FRAU and codec information including codec type and codec configuration for the compressed content in the radio network. A type of a FRAU may serve as an indication of how to process the content frames, for example for the case that the processing in the MGW does not involve any transcoding. According to a variant of this aspect of the invention, the conversion mode comprises transparently forwarding the compressed content of the content frames, i.e. the processing in the MGW does not involve any transcoding. In an alternative variant, the conversion mode comprises transcoding the compressed content of the content frames. For example, the processing may comprise to transcode the received compressed content into a PCM signal. For instance, the conversion mode may comprise inserting at least one of tones and announcements.

In one representation of this aspect of the invention, each content frame comprises control information specific for the core network, and the conversion mode comprises a frame adaptation with changing the core network specific control information to a destination network specific control information. The destination network may, e.g., be the core network (i.e., the content frames are adapted for a core network interface such as an Nb interface), a POTS or IP-network, or another radio network (i.e., the content frames are adapted for an interface such as an Iu-interface in an UMTS network).

According to a fifth aspect of the invention, a still further method of controlling a communication over a telecommunication system is proposed, in which the commu- nication comprises a transfer of content frames including compressed content between a media gateway (MGW) in a core network of the telecommunication system and a frame adaptation unit (FRAU) in a radio network of the telecommunication system without transcoding of the content frames between the MGW and the FRAU and without codec negotiation between the MGW and the FRAU. The method com- prises, at the MGW, the steps of receiving, from a master node associated with at least one of the MGW and the FRAU, signalling related to the communication;; receiving content frames from a source of the communication; converting the received content frames, based on the received signalling, according to a conversion mode; and sending the converted content frames towards the FRAU.

Whereas the fourth aspect of the invention relates to an uplink direction of the communication, the fifth aspect relates to a downlink direction. The modes, implementations and variants summarized above for the fourth aspect of the invention therefore apply analogously also to the fifth aspect. For example, the signalling received from the master node may be the identical signalling for the third and the fourth aspect. The content frames may be sent towards the FRAU transported over a PCM link. The conversion mode may then comprise inserting the content frames in one or more least significant bits. Therefore the MGW may avoid generating a PCM signal towards the radio network.

According to a sixth aspect of the invention, a method of controlling a communication in a MGW is proposed, in which the communication comprises a transfer of content frames in uplink direction and in downlink direction at a MGW. The method comprises the steps of the fourth and the fifth aspect of the invention.

According to a seventh aspect of the invention, a computer program product is proposed comprising program code portions for implementing the steps of any one of the method aspects described herein when the computer program product is executed on one or more computing devices, for example in a FRAU or a MGW in a mobile network such as an UMTS or LTE network. The computer program product may be stored on a computer readable recording medium, such as a permanent or re-writeable memory within or associated with a computing device or a removable CD-ROM or DVD. Additionally or alternatively, the computer program product may be provided for download to a computing device, for example via at least one of a data network, a cable and a wireless link.

According to an eighth aspect of the invention, a frame adaptation unit (FRAU) for performing a method of controlling a communication over a telecommunication system is proposed, wherein the communication comprises a transfer of content frames including compressed content between the FRAU in a radio network of the telecommunication system and a media gateway (MGW) in a core network of the telecommunication system without transcoding of the content frames between the FRAU and the MGW and without codec negotiation between the FRAU and the MGW. The FRAU comprises a signalling reception component adapted to receive signalling related to the communication from a master node associated with the FRAU; a frame reception component adapted to receive content frames of the communication from within the radio network; a adaptation component adapted to adapt the received content frames, based on the received signalling, to an interface between the radio network and the core network; and a transmission component adapted to send the adapted content frames to the MGW. According to a ninth aspect of the invention, a frame adaptation unit (FRAU) for performing a method of controlling a communication over a telecommunication system is proposed, wherein the communication comprising a transfer of content frames including compressed content between a media gateway (MGW) in a core network of the telecommunication system and the FRAU in a radio network of the telecommunication system without transcoding of the content frames between the MGW and the FRAU and without codec negotiation between the MGW and the FRAU. The FRAU comprises a signalling reception component adapted to receive signalling related to the communication from a master node associated with at least one of the FRAU and the MGW; a frame reception component adapted to receive content frames of the communication from the MGW; an adaptation component adapted to adapt the received content frames, based on the received signalling, to a radio network interface; and a transmission component adapted to send the adapted content frames into the radio network.

A frame adaptation unit may comprise all the components according to the eighth and the ninth aspect of the invention. . . . . . - -

According to a tenth aspect of the invention, a media gateway (MGW) for performing a method of controlling a communication over a telecommunication system is pro- posed, wherein the communication comprises a transfer of content frames including compressed content between a frame adaptation unit (FRAU) in a radio network of the telecommunication system and the MGW in a core network of the telecommunication system without transcoding of the content frames between the FRAU and the MGW and without codec negotiation between the FRAU and the MGW. The MGW comprises a signalling reception component adapted to receive signalling related to the communication from a master node associated with at least one of the FRAU and the MGW, , a frame reception component adapted to receive content frames from the FRAU, a conversion component adapted for converting the received content frames, based on the received signalling, according to a conversion mode, and a transmission component adapted to send the converted content frames towards a destination of the communication.

According to an eleventh aspect of the invention, a media gateway (MGW) for performing a method of controlling a communication over a telecommunication system is proposed, wherein the communication comprises a transfer of content frames including compressed content between the MGW in a core network of the telecommunication system and a frame adaptation unit (FRAU) in a radio network of the telecommunication system without transcoding of the content frames between the MGW and the FRAU and without codec negotiation between the MGW and the FRAU. The MGW comprises a signalling reception component adapted to receive signalling related to the communication from a master node associated with at least one of the FRAU and the MGW; a frame reception component adapted to receive content frames from a source of the communication; a conversion component adapted to convert the received content frames, based on the received signalling, according to a conversion mode; and a transmission component adapted to send the converted content frames towards the FRAU. A media gateway may comprise all the components according to the tenth and the eleventh aspect of the invention.

According to a twelfth aspect of the invention, a telecommunication system is proposed, which comprises a FRAU according to the eighth and ninth aspect of the in- vention and a MGW according to the tenth and eleventh aspect of the invention. The FRAU and the MGW may be associated to each other via static configuration.

Brief Description of the Drawings

In the following, the invention will further be described with reference to exemplary embodiments illustrated in the figures, in which:

Fig. 1 schematically illustrates a first embodiment of a telecommunication system including a radio network and a core network;

Fig. 2 schematically illustrates a second embodiment of a telecommunication system;

Fig. 3 schematically illustrates an ongoing communication within the telecom- munication system of Fig. 2;

Fig. 4 is a functional block diagram schematically illustrating an embodiment of a frame adaptation unit;

Fig. 5 is a function block diagram schematically illustrating an embodiment of a media gateway ; Fig. 6 is a flow chart illustrating steps of a first method embodiment for controlling a communication over a telecommunication system in a FRAU;

Fig. 7 is a flow chart illustrating steps of a second method embodiment for controlling a communication over a telecommunication system in a

FRAU;

Fig. 8 is a flow chart illustrating steps of a first method embodiment for controlling a communication over a telecommunication system in a MGW;

Fig. 9 is a flow chart illustrating steps of a second method embodiment for controlling a communication over a telecommunication system in a MGW;

Fig. 10 is sequence diagram illustrating a message flow in an embodiment of a telecommunication system;

Fig. 11 is a schematic illustration of third embodiment of a telecommunication system.

Detailed Description

In the following description, for purposes of explanation and not limitation, specific details are set forth, such as specific network topologies including particular network nodes, communication protocols etc., in order to provide a thorough understanding of the current invention. It will be apparent to one skilled in the art that the current invention may be practised in other embodiments that depart from these specific details. For example, the skilled artisan will appreciate that the current invention may be practised with communications systems different from systems comprising the GERAN radio network discussed below to illustrate the present invention. The invention may in fact be practised with any telecommunication system in which compressed content is transported. This includes all communication networks with a radio or air interface and therefore besides mobile networks e.g. wireless networks, as the transmission of data via such an interface may generally require compressing content data for bandwidth efficiency reasons. The content may not only comprise speech data, but may comprise any kind of data which can be compressed, e.g. video data.

Those skilled in the art will further appreciate that functions explained hereinbelow may be implemented using individual hardware circuitry, using software functioning in conjunction with a programmed microprocessor or a general purpose computer, using an application specific integrated circuit (ASIC) and/or using one or more digital signal processors (DSPs). It will also be appreciated that when the current invention is described as a method, it may also be embodied in a computer processor and a memory coupled to a processor, wherein the memory is encoded with one or more programs that perform the methods disclosed herein when executed by the processor.

Fig. 2 schematically illustrates an embodiment of a telecommunication system 200 in which the invention may be practised. The system 200 may be an UMTS network including a GERAN radio access network (not explicitly illustrated in Hg. 2). An MSC 202 has a BSC 204 associated therewith. The MSG further controls a MGW 206 in a core network, e.g. an MSS-CN, of the system 200. The BSC 204 controls a frame adaptation unit (FRAU) 208.

Assuming exemplarily that the system 200 is an implementation of the system 160 of Fig. 1, the MSC 202 and MGW 206 may be implementations of MSC 130 and MGW 140, respectively. The BSC 204 may be an implementation of the BSC 125 of Fig. 1. The FRAU 208 may replace the TRAU 115 of Fig. 1 or may be provided in parallel to the TRAU, e.g. may be implemented within the TRAU 115 or separately from the TRAU 115.

It is assumed in Fig. 2 that a speech call is set up. The MSC 202 and the BSC 204 may negotiate a codec to be used over the A-interface 210. The negotiation proce- dure 212 may comprise that the BSC 204 sends an indication of one or more codecs to the MSC 202. The codec negotiation 212 may be completed by sending an indication of a desired codec from the MSC 202 to the BSC 204. The BSC 204 may or may not acknowledge the reception of the desired codec to the MSC 202. The BSC 204 may adopt the desired codecand may accordingly control the FRAU 208 as described further below. The possibility that the BSC 204 does not adopt the desired codec may be excluded, e.g. by configuring the BSC 204 accordingly or by ensuring that there is no reason for the BSC to discard the desired codec by, e.g., providing sufficient re- sources over the radio interface served by the BSC. As another possibility, in cases in which the BSC 204 does not agree with the desired codec, the BSC may use a conventional TRAU such as the TRAU 115 in Fig. 1 instead of the FRAU 208 in Fig. 2.

The MSC 202 and the BSC 204 have successfully negotiated a common codec, as described above. Therefore, both have the information which codec is to be used over the A interface 210 and may instruct their associated transport node accordingly. In detail, the MSC 202 informs the associated MGW 206 via signalling 216 of the used codec and the BSC 204 informs its associated FRAU 208 via signalling 214 of the used codec. For example, the signalling 214 / 216 may include an indication of the used codec. In this way, the codec negotiation in the control plane and the subsequent signalling of the used codec down to the user plane ensures that the same or a compatible codec is used between the FRAU and the MGW.

The information on the used codec is applied for adapting speech frames in the FRAU 208 and is applied for converting speech frames in the MGW 206, as will be described in more detail below. As to the general notation used herein, an "adaptation" of content frames (e.g., speech frames) is meant to not include any transcoding of content (e.g., speech) of the content frames, whereas a "conversion" of content frames may or may not include a transcoding of content of the content frames.

Compressed speech frames in TRAU format arrive over the Ater interface 218 at the FRAU 208. The FRAU 208 adapts the received speech frames to conform to a TFO format as known from TS 28.062. In this respect, the FRAU 208 appropriately adapts control bits included in the speech frames. No transcoding of the compressed speech is performed in the FRAU 208. The FRAU 208 forwards the speech frames without a prior TFO negotiation over the A-interface 210 towards the MGW 206.

The MGW 206 accepts the compressed speech frames in TFO format from the FRAU 208, although no TFO negotiation has been performed. It converts the frames ac- cording to the requirements for the further call path, i.e. the Nb-interface 220. For example, the MSC 202 may have successfully negotiated the desired codecs also further along the uplink direction, e.g. via OoBTC (not shown in Fig. 2). In that case, no transcoding may be required also in the MGW 206, which therefore only forwards the received speech frames with or without an adaptation of the control information. In other cases, a transcoding (e.g. into a PCM signal) may additionally be required for transport over the Nb-interface 220. A similar processing as has been described for the uplink direction Ater - A - Nb may also be performed in the downlink direction Nb - A - Ater.

Fig. 3 schematically illustrates a speech data flow in an embodiment of a telecommu- nication system 300 from a mobile station 302 over a FRAU 304 to a MGW 306 in a core network of the system 300. Control entities such as MSC and BSC have been omitted in the figure.

Speech is encoded with an AMR-WB in the MS 302. The encoded (compressed) speech is transported in one of four 16 kilobyte channels of a communication link over the Ater interface to the FRAU 304. The FRAU 304 extracts the compressed speech frame from the corresponding channel and enters the compressed speech frames into the two least significant bits of a PCM data stream indicated as ¹TFO* " sent over the A-interface. As illustrated in Fig. 3, no decoder is used in the FRAU 304 for transcoding the compressed speech signal. Depending on the implementation, no decoder may actually be present in the FRAU 304.

As the compressed speech is not decoded, it is not possible to generate a PCM signal. Consequently, instead of a PCM signal, the six most significant bits of the PCM stream towards the MGW 306 are filled with a predefined, constant value indicated as "0" in Fig. 3. In an alternative embodiment, the unused most significant bits of the PCM stream transport one or more other data streams comprising, e.g., compressed speech associated with other speech connections. The TFO* data stream is transmitted to the MGW 306. The described handling in the FRAU 304 is performed already for the first speech frame arriving received from the mobile station 302. No codec negotiation is performed between the FRAU 304 and the MGW 306.

The MGW 306 discards the most significant bits of the PCM data stream, extracts the AMR compressed speech frames from the least significant bits and repacks the frames into Nb-frames (in an alternative embodiment, the extracted frames are repacked into Iu-frames). These frames may then be sent via ATM or RTP/IP over the Nb-(or Iu-)interface further along the call path.

Fig. 4 illustrates functional components of an embodiment of a FRAU 400. The FRAU 400 may, e.g., be an implementation of the FRAU 208 or 304 of the foregoing fig- ures. The FRAU 400 may be located in the radio network of a telecommunication system, for instance a GERAN, and is adapted to transport content from an Ater- interface 402 to an A-interface 404 and/or vice versa. The FRAU 400 may be controlled by an associated BSC via a signalling link 406.

The FRAU 400 comprises a signalling reception component 408, which is adapted to receive signalling 406 related to the communication from a master node associated with at least one of the FRAU 400 and a MGW situated behind the A-interface 404. For example, the master node may be a BSC associated with the FRAU 400 or an MSC associated with the BSC, the FRAU 400, or the MGW.

The FRAU 400 further comprises a first frame reception component 410, which is adapted to receive content frames of an ongoing communication, e.g. a speech call, from the radio network via the Ater-interface 402. The FRAU 400 further comprises a first adaptation component 412, which is adapted to adapt the received content frames based on the received signalling 406. The adaptation component 412 may access a storage component 414, which stores mapping tables for mapping control information bits included in a speech frame according to a TRAU frame format into a TFO frame format. For instance, the signalling 406 may be a trigger signal, in response to which the signalling component 408 activates the adaptation component 412, which in turn performs a proper replacement of control information bits in the received speech frames according to the mapping instructions extracted from the storage 414. In an alternative embodiment, the signalling 406 may indicate a codec. The signalling component 408 may determine a set of replacement rules on the basis of the received codec indication and may provide the replacement rules to the adaptation component 412.

The adaptation component 412 provides the adapted frames, in which the bits representing compressed speech have been retained unchanged, to a first transmission component 416, which transmits the adapted speech frames over the A-interface 404.

So far, the adaptation of speech frames received in an uplink direction has been described. A similar handling is performed in the downlink direction. In this regard, the signalling 406 may trigger also the downlink handling. For example, a codec information may comprise an indication of the codec which is used in the uplink, and may comprise an indication of the codec which is used in the downlink. The FRAU 400 comprises a second frame reception component 418, which is adapted to receive content frames of the communication from a MGW over the A-interface 404. The reception component 418 provides the received frames to second adaptation compo- nent 420, which is adapted to adapt the received content frames based on the received signalling 406. For example, the component 420 may discard a PCM-signal (if any) received and may adapt the frames according to the mapping tables held in the storage 414. A second transmission component 422 is provided which is adapted to send the adapted content frames to the radio network over the Ater-interface 402.

Fig. 5 schematically illustrates functional components of an embodiment of a MGW 500. The MGW 500 may, e.g., be an implementation of the MGW 206 or 306 of the foregoing figures. The MGW 500 may be located in the core network of a telecom- munication system, for instance a UMTS network, and is adapted to transport content received at an A-interface 502 to an Nb-interface 504 and vice versa.

The MGW 500 comprises a signalling reception component 508, which is adapted to receive signalling related to the communication from a master node associated with at least one of a FRAU located behind the A-interface 502 and the MGW 500. The master node may be an MSC controlling the MGW 500. The MGW 500 further comprises a first conversion component 510 which is adapted to convert received content frames, based on the received signalling, according to a conversion mode for a communication over the A- and Nb-interfaces. Preparing the conversion mode may com- prise to decide if the conversion component 510 is to be inserted or activated in the path of content frames from the A-interface 502 to the Nb-interface 504. In case a conversion, e.g. comprising a transcoding, has to be performed, the conversion component 510 may access a storage component 512, which stores codec information for de- and encoding the received compressed speech. For instance, the signalling 506 from the master node may comprise an indication of a codec required for further transmission of the content frames over the Nb-interface 504. In response to the signalling the reception component 508 activates the conversion component 510, which in turn prepares a proper transcoding of information bits representing a content according to the transcoding instructions extracted from the storage 512. For example, a conversion to a PCM signal may be required in the conversion component 510 as no common codec is available further along the call path. The conversion component 510 may transcode compressed speech into a PCM signal according to the G.711 codec.

The transcoding component 510 may further access a storage component 514, which stores mapping tables for mapping control information included in the received speech frames into a format as required for the further transport over the Nb interface 504.

The media gateway 500 further comprises a first frame reception component 516, which is adapted to receive content frames over the A-interface 502. A first transmis- sion component 518 is adapted to send the converted content towards a destination of the communication via the Nb-interface 504.

So far, the transcoding of content frames has been described in the uplink direction, i.e. from the A-interface 502 towards the Nb-interface 504. The handling of content frames in the downlink direction, i.e. from the Nb-interface 504 towards the A- interface 502, proceeds similarly. In this regard, the MGW 500 comprises a second conversion component 520, which is adapted to convert, based on a received signalling and according to a conversion mode, content frames which have been received by a second frame reception component 522, which is in turn adapted to receive content frames from a source of the communication over the Nb-interface 504. The MGW 500 further comprises a second transmission component 524, which is adapted to send the converted content frames towards a FRAU over the A-interface 502.

Depending on the used codecs over the Nb- and the A-interface, the conversion component 520 transcodes content received over the Nb-interface 504 into compressed speech over the A-interface 502. The conversion component 520 may access the required de-/encoding information from the storage component 512 in a preparatory phase. In other embodiments, no transcoding may be required, in which case the conversion component 520 may not be inserted into the call path. In still other embodiments, the conversion component is inserted into the call path although no transcoding is required, e.g. because a frame adaptation has to be performed.

In summary, the conversion components 510 and 520 may incorporate functions of a TRAU (a component of radio access networks), although the MGW 500 may be lo- cated in a core network.

Hg. 6 is a flow diagram illustrating steps of a method 600 of controlling a communication over a telecommunication system, in which the communication comprises a transfer of content frames including compressed content between a frame adaptation unit in a radio network of the telecommunication system and a media gateway in a core network of the telecommunication system without transcoding of the content frames between the FRAU and the MGW and without codec negotiation between the FRAU and the MGW. The method may be performed in one of the FRAUs 208, 304 or 400 depicted in the forgoing figures.

The method starts in step 602 with the reception of signalling related to the commu- nication from the master node associated with at least one of the FRAU and the MGW. For example, a trigger signal may be received from an MSC either directly or via a BSC associated with the FRAU. In step 604, content frames of the communication are received from within the radio network, e.g. another node in the radio network such as a BTS. In step 606, the received content frames are adapted, based on the signalling received from the control node in step 602, to an interface between the radio network and the core network. In step 608, the adapted content frames are sent to the MGW, e.g. over an A-interface in a GSM or UMTS network. The method returns control in step 610 to a higher layer control program in the FRAU.

Fig. 7 illustrates a step a method embodiment 700 of a further method for controlling a communication over telecommunication system, in which the communication comprises a transfer of content frames including compressed content between a frame adaptation unit in a radio network of the telecommunication system and a media gateway in a core network of the telecommunication system without transcoding of the content frames between the FRAU and the MGW and without codec negotiation between the FRAU and the MGW. The method 700 may be implemented additionally or alternatively to the method 600 in a FRAU such as the FRAUs 208, 304 and 400 of the foregoing figures.

The method is triggered in step 702 by the reception of signalling related to the communication from the master node associated with the FRAU. The received signalling may or may not be identical to the signalling received in step 602 in the method embodiment 600. For example, the signalling may trigger the activation of both adaptation components 412 and 420 in the FRAU 400 of Fig. 4.

In step 704, content frames of the communication are received from the media gateway. For example, in case the FRAU is located in a GERAN radio network, the content frames may be received over the A-interface. In step 706, the received content frames are adapted, based on the received signalling, on a radio network interface, e.g. an Ater interface. In step 708, the adapted content frames are sent into the radio network; e.g. in a GERAN network, the frames are sent over the Ater-interface towards a BTS. When the communication ends or a different codec has to be em- ployed during a communication, the method returns control to a higher layer control program in step 710.

Fig. 8 is flow diagram illustrating steps of an embodiment of a method 800 of con- trolling a communication over telecommunication system, the communication comprising a transfer of content frames including compressed content between a frame adaptation unit (FRAU) in a radio network of the telecommunication system and a media gateway (MGW) in a core network of the telecommunica-tion system without transcoding of the content frames between the FRAU and the MGW and without codec negotiation between the FRAU and the MGW. The method 800 may be performed in the MGW, e.g. in any one of the MGWs 206, 306 and 500 of the foregoing figures.

The method starts in step 802 with the reception of signalling related to the commu- nication from a master node associated with at least one the FRAU and the MGW. For example, H.248 or MEGACO signalling may be received from an MSC server associated with the MGW. In step 804, content frames of the communication are received from the FRAU. In step 806, the received content frames are converted, based on the received signalling, according to a conversion mode. In step 808, the converted content frames are sent towards a destination of the communication. For example, the frames may be sent further into the core network or into another radio network, e.g. a GERAN or UTRAN. The method eventually returns control to a higher layer control program in step 810.

Fig. 9 illustrates steps of another method embodiment 900 of controlling a communication over a telecommunication system, the communication comprising a transfer of content frames including compressed content between a media gateway (MGW) in a core network of the telecommunication system and a frame adaptation unit (FRAU) in a radio network of the telecommunication system without transcoding of the con- tent frames between the MGW and the FRAU and without codec negotiation between the MGW and the FRAU. The method 900 may additionally or alternatively to the method 800 be implemented in any one of the MGWs 206, 306 or 500. Method embodiment 800 relates to an uplink transport direction and method 900 relates to a downlink transport direction.

The method starts in step 902 with the reception of signalling related to the communication from a master node associated with at least one of the MGW and the FRAU. This signalling may or may not be the identical signalling received in step 802 in method implementation 800.

In step 904, content frames are received from a source of the communication, which may be, e.g., a mobile station at the distant end of the communication path. In step 906, the received content frames are converted, based on the received signalling, according to a conversion mode. For example, the conversion mode may comprise to transcode a PCM signal received from the core network into a stream of content frames including compressed content according to a particular codec. In step 908, the converted content frames are sent towards the FRAU. The method eventually returns control to a higher layer control program of the MGW in step 910.

Fig. 10 schematically illustrates a call flow 1000 in an embodiment of a telecommunication system. The system includes a GERAN comprising a BSC 1002, BTS 1004 and FRAU 1006, a core network comprising a MGW 1008 and an MSC 1010, and an UTRAN comprising an RNC 1012. Terminating entities such as a calling and a called party are not shown in Fig. 10. The FRAU 1006 may be implemented as a standalone entity or may be integrated into an existing TRAU equipment (not shown). With a message 1014, the MSC 1010 indicates a desired codec to the BSC 1002. The BSC 1002 agrees with the desired codec and provides signalling messages 1016 and 1018 to its associated nodes BTS 1004 and FRAU 1006, respectively, in order to trigger resource allocation therein. The messages 1016 and 1018 may each comprise an indication of the desired codec. Similarly, the MSC 1010 instructs the MGW 1008 in the core network via H.248 signalling 1020 on the used codec.

In response to an instruction 1022 received from the BTS 1004, the FRAU 1006 transmits a Generic Configuration Frame 1024 according to the TFO standard specified in TS 28.062 via the A-interface to the MGW 1008. The Con_Rec / Con_Ack message exchange is not mandatory, but may primarily be used to ensure proper error handling, as the desired codec is already known to the FRAU 1006 and MGW 1008.

There may be numerous message exchanges over the Ater-interface between the BTS 1004 and the FRAU 1006, from which only time-alignment messages 1026 and TFO_Soon messages 1028 are exemplarily illustrated in Fig. 10. Some of these mes- sages are proprietary, i.e. implementation dependent (e.g., at least one of vendor and release dependent). Such proprietary messages must not appear on the A- interface. Therefore the FRAU 1006 operates to eliminate proprietary Ater messages in uplink direction.

In the uplink direction indicated by arrow 1030 in Fig. 10, the BTS 1004 forwards compressed speech frames 1032 over the Ater-interface to the FRAU 1006. The speech frames 1032 are sent in a TRAU format, i.e. the BTS 1004 utilizes the same format for speech frames regardless if the frames are provided towards a TRAU or the FRAU 1006. In the FRAU 1006, the compressed speech frames 1032 are adapted from the TRAU format of the Ater-interface to the TFO format known from TS 28.062 for the A-interface. TFO frames 1034 are then sent over the A-interface towards the MGW 1008, without any prior TFO negotiation. No decoder and encoder is utilized in the FRAU 1006. The A-interface between FRAU 1006 and the MGW 1008 is also called TFO interface with respect to the exchange of speech frames in a TFO conformant format (cf. TS 28.062).

While Fig. 10 illustrates that a negotiation may be performed between MSC 1010 and BSC 1002 to make a negotiation between the transport nodes 1006 and 1008 superfluous, various other possibilities exist to achieve this goal. For example, the BSC may be configured to always use the desired codec signalled from the MSC, and may then trigger a corresponding FRAU in the radio network accordingly. Only in case no matching FRAU is available, the BSC may be forced to use a different codec and may then trigger a TRAU instead.

Referring further to Fig. 10, the MGW 1008 may forward the received compressed speech frames 1034 without transcoding as Iu frames 1036 towards the RNC 1012, assuming that the same or a TFO compatible speech codec is used between the FRAU 1006 and MGW 1008 and on the Iu interface. In case different speech codecs are used on the interfaces, the MGW 1008 has to perform transcoding.

In the downlink direction, which is indicated by arrow 1038, similar procedures are performed as described for the uplink direction 1030. In particular, the MGW 1008 converts Iu frames 1040 received from the RNC 1012 without transcoding into TFO frames 1042 and forwards these frames 1042 via the A interface towards the FRAU 1006. The FRAU performs an adaptation of the received TFO frames 1040 into TRAU frames 1044 and forwards the frames 1044 to the BTS 1004. The signalling 1018 does not necessarily comprise the desired codec. In one embodiment, the adaptation handling performed in the FRAU 1006 may be identical for different codecs; for example, a particular handling may be identical for all codecs of the AMR codec family. In case a FRAU is specially configured to perform such AMR handling, in principle a 1-bit trigger signal from the BSC would be sufficient to activate the FRAU, for example in case the FRAU is statically assigned to a BTS over the Ater-interface and a MGW over the A-interface for speech calls. The trigger signal may then lead to the allocation of the appropriate resources. In another embodiment, TRAU frames according to a particular standard may also contain in its frame header all information required to determine a desired conversion. A FRAU configured to receive such frames, e.g., via the Ater interface may also need in principle only a 1-bit activation signal.

Referring back to Fig. 1, which shows that the radio network 170 also comprises a Handover-Handler (HoH) 120 inserted in the call path between the TRAU 115 and the MGW 140. The HoH 120 handles BSC-internal handover (HOV) scenarios. In this respect, the HoH 120 is in general connected to different TRAUs (not shown in Fig. 1). Whereas the HoH 120 is shown as being located directly at the A interface in Fig. 1, in other network scenarios a HoH may alternatively be located at the Ater interface or the Abis interface.

During HOV, the BSC 125 allocates a new BTS and a new TRAU, and also inserts the HoH 120 into the call path. In the downlink direction, the HoH 120 sends received PCM samples from the core network to the old TRAU and the new TRAU. The MS may receive downlink communications from the old and the new BTS, such that speech quality is ensured during HOV. In the uplink direction, the HoH 120 decides to forward either the PCM signal from the old TRAU or from the new TRAU to the core network.

Fig. 11 schematically illustrates an embodiment of a telecommunication system 1100 including a MGW 1102 connected with a HoH 1104 over an A-interface 1106. As for Fig. 1, it is to be noted also for the system 1100 in Fig. 11 that the location of the HoH at the A interface is not mandatory; in other embodiments, the HoH may be located at the Ater or Abis interface. The HoH 1104 is connected with a FRAU 1108, a FRAU 1110, a TRAU 1112 and a TRAU 1114. Available or Selected speech Codecs SC are schematically indicated as numbers ¹Ll¹, ... '2' at each node. Codecs 1.1 and 1.2 are assumed to be compatible to each other, whereas codecs of the codec family 1.x and codec 2 may be incompatible with each other.

A HOV from FRAU 1108 to FRAU 1110 is schematically illustrated by arrow 1116. It is assumed that a compatible codec type is used by the FRAUs 1108 and 1110 during HOV 1116. In this case, the new FRAU 1110 immediately receives TFO speech frames over the A-interface 1106 from the media gateway 1102 and the HoH 1104. In the uplink direction the new FRAU 1110 immediately sends TFO speech frames. Thus, there will be no audible distortion in speech apart from a possible, very short distortion at the switching time point.

The schematically indicated HOV 1118 is performed from the FRAU 1110 to a TRAU 1112, the latter using the conventional TFO protocol. Here it is assumed that the involved speech codecs are compatible to each other, as for the HOV 1116. In this case the new, conventional TRAU 1112 detects the TFO speech frames and immediately applies the corresponding TFO mode without requiring a TFO negotiation phase. Therefore it is of no matter if the MGW 1102 provides a PGM signal or not, as the PCM signal is not used. A similar situation occurs for a HOV 1120 from the old TRAU 1112 to the new FRAU 1110: The interworking of TRAU and FRAU in HOV scenarios poses no problems in case the codec types are the same or at least compatible. The MGW 1102 must of course be adapted for interworking with both, FRAU and TRAU. For example, the MGW 1102 must have implemented a minimum set of TFO messages for TFO message exchange with the conventional TRAU 1112.

A further HOV case from a first FRAU to another FRAU with a change to an incompatible codec should be excluded because a FRAU might only be provided for a compatible codec type, i.e. a codec type which can be handled in the MGW without reconfiguration. A HOV with a change to an incompatible codec type can thus not be handled within the radio network. However, instead a HOV to a TRAU might be per- formed, which will be described next.

The HOV 1122 from FRAU 1108 to TRAU 1114 exemplarily illustrates this class of HOV scenarios from a FRAU to a conventional TRAU with incompatible codecs. The conventional TRAU 1114 requires at least a TFO negotiation phase, during which a PCM signal must be used. In case the MGW 1102 does not provide a PCM signal, no speech signal would be present in the downlink direction in Fig. 11. Therefore the MGW 1102 has to provide a PCM signal. As the core network will generally not be informed on a radio network internal HOV, the MGW 1102 has to provide a PCM signal towards the radio network permanently. This requirement may however be abandoned and processing resources may be saved within the MGW, if it is assured that codecs are used during a communication which are compatible to each other.

An inherent feature of mobile communication systems is that core network nodes are arranged in a centralized fashion while radio network nodes are more decentralized and distributed over the coverage area of the mobile communication system. Hence, typically much more radio network nodes than core network nodes exist and any costly functionality that could be transferred from a plurality of radio network nodes to a centralized core network node would result in reasonable cost savings.

The techniques proposed herein allow to reduce the number of transcoding operations at least in a radio network for a communication, e.g., for speech calls. Further, the technique allows to establish such a communication in a particularly fast and efficient way. For example, a TFO connection may be established over the interface between a radio network, e.g. a GERAN, and a core network of a mobile communica- tion system, before the first speech is transported over the A-interface such that no audible distortions can occur. Whereas known TFO-based techniques only bypass transcoding functionality implemented in transport nodes such as TRAUs, the techniques proposed herein allow to entirely eliminate transcoding functionalities. For example, a pool of TRAUs in a radio network may at least in part be replaced by a pool of FRAUs.

The proposed techniques may comprise the employment of frame adaptation units (FRAU), and each FRAU may replace one or more conventional TRAUs in a radio network. Therefore, costly transcoder equipment (hardware and software) as well as the corresponding footprint may be saved for the radio access network; implementa- tion and maintenance costs can also as be reduced. A TRAU hardware may be reused for the FRAU tasks. For example, a conventional TRAU board may handle a maximum of N speech traffic channels, but may be able to handle as much as k*N speech traffic channels if only frame adaption without transcoding is to be performed; k may have a value as large as 10. A FRAU without transcoder may save of order 90% or more of processing resources in comparison to a conventional TRAU. The adaptation of control information bits, e.g. between a TRAU format and a TFO format, may be identical for different speech codecs such as the codecs of the AMR codec set and, in some embodiments, also for EFR codecs. Therefore, a single FRAU implementation may serve to adapt frames according to a plurality of frame formats.

A FRAU may appear much as a TRAU when seen from other nodes. Therefore, no modifications are required in the control nodes, e.g. the BSC or BTS in a GERAN network. The FRAU may, e.g., handle tasks like shielding the A-interface from proprietary Ater-messages, rate control, etc.

In one realization of a telecommunication system, only FRAUs may be provided in the radio network, such that no transcoding is performed at all in the radio network. Any transcoding required may only be performed in the core network, e.g. in the transport media gateways. According to an additional or alternative aspect of the pro- posed technique, no conventional TFO setups may be performed in a telecommunication system, i.e. the slow TFO negotiation phase is completely avoided at least over the interface between radio network and core network. Then the TFO implementation in the corresponding "edge" nodes, e.g. FRAU and MGW, can be simplified.

The proposed techniques may comprise that no PCM signal is generated in a FRAU and/or MGW. Therefore, resources are required at the A interface only for the transfer of the compressed content frames. The unused capacity of the communication link between FRAU and MGW may, e.g., be used for other communications (content streams).

While the current invention has been described in relation to its preferred embodiments, it is to be understood that this description is for illustrative purposes only. Accordingly, it is intended that the invention be limited only by the scope of the claims appended hereto.

Claims

1. A method of controlling a communication over a telecommunication system (200), the communication comprising a transfer of content frames including compressed content between a frame adaptation unit (FRAU, 208) in a radio network of the telecommunication system and a media gateway (MGW, 206) in a core network of the telecommunication system without transcoding of the content frames between the FRAU (208) and the MGW (206) and without codec negotiation between the FRAU (208) and the MGW (206), the method comprising the following steps at the FRAU (208):

- receiving (602), from a master node (202) associated with at least one of the FRAU and the MGW, signalling (214) related to the communication;

- receiving (604) content frames of the communication from within the radio network,

- adapting (606) the received content frames, based on the received signalling, to an interface (210) between the radio network and the core network; and

- sending (608) the adapted content frames to the MGW (206).

2. The method according to claim 1, wherein the signalling (214) comprises an indication of the requested frame adaptation.

3. The method according to claim 2, wherein the master node (1010) is a communication control node (1010) in the core network, a codec information indicating a codec to be used for the communication is transmitted from the communication control node (1010) to a base station controller (1002) in the radio network, and the signalling relates to the codec indicated in the codec information.

4. The method according to claim 3, wherein a codec negotiation is performed between the communication control node (202) in the core network and the base station controller (204) in the radio network.

5. The method according to any one of the preceding claims, wherein each content frame comprises control information specific for the radio network, and wherein the adaptation of the content frames comprises changing the radio network specific control information to core network specific control information.

6. The method according to any one of the preceding claims, wherein the interface between the radio network and the core network is a TFO interface.

7. The method according to any one of the preceding claims, comprising the steps of generating a data stream comprising the adapted content frames, and sending the data stream to the MGW.

8. The method according to claim 7, wherein the data stream is transported over a PGM link and the adapted compressed content frames are sent in one or more least significant bits.

9. The method according to any one of the preceding claims, comprising the step of sending, upon receipt of the signalling, a message (1018) indicative of the signalling to the MGW.

10. The method according to any one of the preceding claims, wherein the signalling from the master node is received in a set-up phase of the communication or in a codec changing phase during the ongoing communication.

11. The method according to any one of the preceding claims, wherein the content frames are TRAU frames received at the FRAU via an Ater inter- face and sent as TFO frames to the MGW via an A interface.

12. A method of controlling a communication over a telecommunication system (200), the communication comprising a transfer of content frames including compressed content between a media gateway (MGW, 206) in a core network of the telecommunication system and a frame adaptation unit (FRAU, 208) in a radio network of the telecommunication system without transcoding of the content frames between the MGW (206) and the FRAU (208) and without codec negotiation between the MGW (206) and the FRAU (208), the method comprising the following steps at the FRAU (208):

- receiving (702), from a master node (202) associated with at least one of the FRAU and the MGW, signalling (214) related to the communication;

- receiving (704) content frames of the communication from the MGW (206);

- adapting (706) the received content frames, based on the received signalling, to a radio network interface (218); and

- sending (708) the adapted content frames into the radio network.

13. A method of controlling a communication comprising a transfer of content frames in uplink direction and in downlink direction at a FRAU (200, 400), the method comprising the steps of claim 1 and claim 13.

14. A method of controlling a communication over a telecommunication system (200), the communication comprising a transfer of content frames including compressed content between a frame adaptation unit (FRAU, 208) in a radio network of ^" the telecommunication system and a media gateway (MGW, 208) in a core network of the telecommunication system without transcoding of the content frames between the FRAU (208) and the MGW (206) and without codec negotiation between the FRAU (208) and the MGW (206), the method comprising the following steps at the MGW:

- receiving (802), from a master node (202) associated with at least one of the FRAU and the MGW, signalling (216) related to the communication; - receiving (804) content frames from the FRAU (208);

- converting (806) the received content frames, based on the received signalling, according to a conversion mode; and

- sending (808) the converted content frames towards a destination of the communication.

15. The method according to claim 14, wherein the signalling (1018) is received via the FRAU (1006).

16. The method according to claim 14 or 15, wherein the signalling comprises an indication of the conversion mode.

17. The method according to any one of claims 14 to 16, wherein the signalling comprises an indication of one or both of a type of the FRAU and codec information including codec type and codec configuration for the com- pressed content in the radio network.

18. The method according to any one of claims 14 to 17, wherein the conversion mode comprises transparently forwarding the compressed content of the content frames.

19. The method according to any one of claims 14 to 17, wherein the conversion mode comprises transcoding the compressed content of the content frames.

20. The method according to any one of claims 14 to 19, wherein each content frame comprises control information specific for the core network, . - - and wherein the conversion mode comprises changing the core network specific control information to control information specific for a destination network.

21. The method according to any one of claims 14 to 20, wherein the signalling from the master node is received in a set-up phase of the communication or in a codec changing phase during the ongoing communication.

22. A method of controlling a communication over a telecommunication system (200), the communication comprising a transfer of content frames including compressed content between a media gateway (MGW, 206) in a core network of the telecommunication system and a frame adaptation unit (FRAU, 208) in a radio network of the telecommunication system without transcoding of the content frames between the MGW (206) and the FRAU (208) and without codec negotiation between the MGW (206) and the FRAU (208), the method comprising the following steps at the MGW (206):

- receiving (902), from a master node (202) associated with at least one of the MGW and the FRAU, signalling (216) related to the communication; - receiving (904) content frames from a source of the communication;

- converting (906) the received content frames, based on the received signalling, according to a conversion mode; and - sending (908) the converted content frames towards the FRAU.

23. The method according to claim 22, wherein the content frames are sent towards the FRAU transported over a PCM link, 5 and the conversion mode comprises inserting the content frames in one or more least significant bits.

24. A method of controlling a communication comprising a transfer of content frames in uplink direction and in downlink direction at a MGW, the method comprising theo steps of claim 14 and claim 22.

25. A computer program product comprising program code portions for performing the steps of any one of the preceding claims when the computer program product is executed on one or more computing devices. 5

26. The computer program product of claim 25, stored on a computer readable recording medium. . -

27. A frame adaptation unit (FRAU, 400) for performing a method of controlling ao communication over a telecommunication system, the communication comprising a transfer of content frames including compressed content between the FRAU (400) in a radio network of the telecommunication system and a media gateway (MGW) in a core network of the telecommunication system without transcoding of the content frames between the FRAU (400) and the MGW and without codec negotiation be-5 tween the FRAU (400) and the MGW, the FRAU comprising:

- a signalling reception component (408) adapted to receive signalling related to the communication from a master node associated with at least one of the FRAU and the MGW; 0 - a frame reception component (410) adapted to receive content frames of the communication from within the radio network;

- a adaptation component (412) adapted to adapt the received content frames, based on the received signalling, to an interface (404) between the radio network and the core network; and 5 - a transmission component (416) adapted to send the adapted content frames to the MGW.

28. A frame adaptation unit (FRAU, 400) for performing a method of controlling a communication over a telecommunication system, the communication comprising a transfer of content frames including compressed content between a media gateway (MGW) in a core network of the telecommunication system and the FRAU in a radio network of the telecommunication system without transcoding of the content frames between the MGW and the FRAU (400) and without codec negotiation between the MGW and the FRAU (400), the FRAU comprising:

- a signalling reception component (408) adapted to receive signalling related to the communication from a master node associated with at least one of the

FRAU and the MGW;

- a frame reception component (418) adapted to receive content frames of the communication from the MGW;

- an adaptation component (420) adapted to adapt the received content frames, based on the received signalling, to a radio network interface; and

- a transmission component (422) adapted to send the adapted content frames into the_.radio. network. . . . - -

29. A media gateway (MGW, 500) for performing a method of controlling a commu- nication over a telecommunication system, the communication comprising a transfer of content frames including compressed content between a frame adaptation unit (FRAU) in a radio network of the telecommunication system and the MGW (500) in a core network of the telecommunication system without transcoding of the content frames between the FRAU and the MGW (500) and without codec negotiation be- tween the FRAU and the MGW (500), the MGW comprising:

- a signalling reception component (508) adapted to receive signalling related to the communication from a master node associated with at least one of the FRAU and the MGW (500); - a frame reception component (516) adapted to receive content frames from the FRAU;

- a conversion component (510) adapted for converting the received content frames, based on the received signalling, according to a conversion mode; and

- a transmission component (518) adapted to send the converted content frames towards a destination of the communication .

30. A media gateway (MGW, 500) for performing a method of controlling a communication over a telecommunication system, the communication comprising a transfer of content frames including compressed content between the MGW in a core network of the telecommunication system and a frame adaptation unit (FRAU) in a radio net- work of the telecommunication system without transcoding of the content frames between the MGW (500) and the FRAU and without codec negotiation between the MGW (500) and the FRAU, the MGW comprising:

- a signalling reception component (508) adapted to receive signalling related to the communication from a master node associated with at least one of the

FRAU and the MGW (500);

- a frame reception component (522) adapted to receive content frames from a source of the communication;

- a conversion component (520) adapted to convert the received content frames, based on the received signalling, according to a conversion mode; and

- a transmission component (524) adapted to send the converted content frames towards the FRAU. _. . _ . - - -

31. A telecommunication system comprising a FRAU according to claims 27 and 28 and a MGW according to claims 29 and 30.

32. The telecommunication system of claim 31, wherein the FRAU and the MGW are associated to each other via static configuration.