MSS_TFO and TrFO Guidelines.pdf

MSS System Documentation, Rel. MSS SR4.0, v.2

TFO and TrFO Guidelines for MSS System

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Table of ContentsThis document has 71 pages.

1 Changes in TFO and TrFO Guidelines for MSS System . . . . . . . . . . . . . 7

2 Overview of TFO and TrFO in MSS System . . . . . . . . . . . . . . . . . . . . . . 82.1 Tandem Free Operation (TFO) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.2 Transcoder Free Operation (TrFO) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.3 Benefits for the operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3 TFO and TrFO features and concepts . . . . . . . . . . . . . . . . . . . . . . . . . . 103.1 Tandem Free (TFO) call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103.2 Transcoder Free (TrFO) call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143.3 TFO and TrFO interworking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163.4 Mobility in TFO/TrFO concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163.5 TFO and TrFO interworking with other services . . . . . . . . . . . . . . . . . . 173.6 Charging and statistics with TFO and TrFO. . . . . . . . . . . . . . . . . . . . . . 183.7 Compliance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

4 TFO and TrFO architecture guidelines . . . . . . . . . . . . . . . . . . . . . . . . . 214.1 Network architecture overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

5 TFO and TrFO configuration guidelines. . . . . . . . . . . . . . . . . . . . . . . . . 275.1 Network support for TFO and TrFO. . . . . . . . . . . . . . . . . . . . . . . . . . . . 275.2 Licences. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295.3 MSS configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325.4 MGW configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425.5 RAN configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435.5.1 Configuring the RNC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435.5.2 Configuring the BSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

6 TFO and TrFO configuration and management. . . . . . . . . . . . . . . . . . . 466.1 TFO and TrFO configuration management use cases. . . . . . . . . . . . . . 466.1.1 TFO configuration in a 2G-2G call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466.1.2 TrFO configuration in a 3G-3G call . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476.1.3 TFO-TrFO interworking configuration . . . . . . . . . . . . . . . . . . . . . . . . . . 486.1.4 Transcoder at Edge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506.2 MGW-MGW interconnect in intra-MSS cases with two MGWs . . . . . . . 516.3 TFO-TrFO configuration example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

7 TFO and TrFO Quality of Service (QoS) . . . . . . . . . . . . . . . . . . . . . . . . 637.1 Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 637.2 Speech quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

8 TFO and TrFO system limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 668.1 Codec types and configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 668.2 2G-3G codec transparency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 668.3 Support in CS Core networks before 3GPP Rel4 . . . . . . . . . . . . . . . . . 678.4 Non-homogeneous radio networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 678.5 Wideband conferencing and announcements . . . . . . . . . . . . . . . . . . . . 678.6 Speech enhancements in TFO and TrFO call . . . . . . . . . . . . . . . . . . . . 68

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9 Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 699.1 Troubleshooting in MGW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 699.2 Troubleshooting in MSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 699.3 Troubleshooting in BSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 709.4 Troubleshooting in UMTS calls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

10 Summary of TFO and TrFO parameters. . . . . . . . . . . . . . . . . . . . . . . . . 7110.1 MSS parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7110.2 MGW parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7110.3 RAN parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7110.4 BSC parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

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List of FiguresFigure 1 Inter-MSS MS to MS speech call with default G.711 codec, tandem free op-

eration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Figure 2 Transcoder free operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Figure 3 TrFO in 3G. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Figure 4 Payload optimization with TFO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Figure 5 Payload optimization with Ater in MGW. . . . . . . . . . . . . . . . . . . . . . . . . 24Figure 6 TFO between PLMNs, with TDM or G.711 (SIP-I, BICC) interconnection.

24Figure 7 TFO-TrFO interworking (2G-3G call) . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Figure 8 Example of 2G TrFO with AoIP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Figure 9 TFO-TrFO configuration at network level. . . . . . . . . . . . . . . . . . . . . . . . 27Figure 10 TRAUs with different AMR TFO support . . . . . . . . . . . . . . . . . . . . . . . . 33Figure 11 New TRAUs coexisting with old TRAUs and Ater interface . . . . . . . . . 34Figure 12 3G-3G inter-MSS call. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37Figure 13 PSTN originated call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38Figure 14 PSTN terminated call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Figure 15 SIP originated call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Figure 16 2G-2G call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46Figure 17 3G-3G call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47Figure 18 2G-3G call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48Figure 19 Transcoder at Edge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50Figure 20 MGW-MGW interconnect. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51Figure 21 Target network transcoding requirements 1 . . . . . . . . . . . . . . . . . . . . . 53Figure 22 Target network transcoding requirements 2 . . . . . . . . . . . . . . . . . . . . . 53Figure 23 NB and WB AMR mode sets for 3G. . . . . . . . . . . . . . . . . . . . . . . . . . . . 56Figure 24 NB and WB AMR mode sets for 2G. . . . . . . . . . . . . . . . . . . . . . . . . . . . 61Figure 25 Call configuration in 2G-3G HD voice call . . . . . . . . . . . . . . . . . . . . . . . 62Figure 26 Estimated subjective MOS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

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List of TablesTable 1 Changes in TFO and TrFO Guidelines for MSS System between MSS

SR3.3, v.3 and SR4.0, v.1 deliveries . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Table 2 TFO and TrFO licences in MGW

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Table 3 FIFILE and PRFILE parameters in MSS . . . . . . . . . . . . . . . . . . . . . . . . 56

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TFO and TrFO Guidelines for MSS System Changes in TFO and TrFO Guidelines for MSS System

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1 Changes in TFO and TrFO Guidelines for MSS SystemThe following changes have been made between Nokia Siemens Networks MSS System Documentation, Rel. SR3.3, v.3 and Rel. SR4.0, v.1 deliveries. The changes are detailed in the table below.

Changes See in

The title of the document has been changed to TFO and TrFO Guidelines for MSS System.

-

The MSS System now supports 3GPP SIP-I TFO-TrFO interworking for supple-mentary services, too.

AMR TFO and TrFO optimization enhancements in Chapter TFO and TrFO features and concepts

10 ms packetization period is available for G.711 codec.

TFO and TrFO interworking with other services in Chapter TFO and TrFO features and concepts

Counter information has been updated. Charging and statistics with TFO and TrFO in Chapter TFO and TrFO features and concepts

CS voice over I-HSPA has been intro-duced.

Network architecture overview in Chapter TFO and TrFO architecture guidelines

Information on A over IP (AoIP) with TC in BSS has been added.

TrFO and TFO codec handling with A over IP in Chapter TFO and TrFO architecture guidelines

Table 1 Changes in TFO and TrFO Guidelines for MSS System between MSS SR3.3, v.3 and SR4.0, v.1 deliveries

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Overview of TFO and TrFO in MSS System

2 Overview of TFO and TrFO in MSS SystemThe present document gives an introduction to the Nokia Siemens Networks speech transmission optimization features, Tandem Free Operation (TFO) and Transcoder Free Operation (TrFO) in the MSS System, and provides guidelines on TFO and TrFO con-figuration planning and management on a system level.

The TFO and TrFO features mean a transmission optimization mechanism, with which either end-to-end codec transparency, bandwidth savings, or both can be achieved on network level. TFO and TrFO are system level functionalities that require support from the radio networks and the MSS System.

To optimally use these features, Nokia Siemens Networks provides system level support starting from the terminals, covering the radio access and CS core domains.

2.1 Tandem Free Operation (TFO)The TFO feature has been available for GSM codecs (EFR, FR, HR) for a long time. In the meantime, the importance of TFO has significantly increased with the introduction of high definition voice with AMR-WB codec. High definition voice in traditional 2G envi-ronment cannot not be provided with existing GSM codecs. Additionally, uncompressed HD speech requires more than 64 kbit bandwidth, which means that such speech has to be transported in a compressed form over the network. This is the reason why TFO is essential with uncompressed HD speech in a 2G network.

TFO has evolved together with the bearer-independent CS core network architecture concept, where control and user plane are separated from each other. Regarding TFO, this evolution has meant similar separation of TFO control and the actual TFO protocol. When the MSC Server (MSS) controls TFO, codec optimization significantly improves because the MSS server controls TrFO, too. End-to-end codec transparency is often achieved by flexible interworking of TFO and TrFO.

The introduction of the AMR codec family has brought more complexity to the TFO func-tionality because of the multimode nature of these codecs. With AMR, not only the codec type, but the multimode configuration also has to be compatible to reach codec transparency. AMR multimode configuration means that terminal and the radio access network are able to switch the used codec rate according to current radio conditions and traffic load.

2.2 Transcoder Free Operation (TrFO)The TrFO feature has been introduced more recently than TFO, and it further improves speech transmission optimization by providing both end-to-end codec transparency and bandwidth saving. TrFO is based on out-of-band codec negotiation and requires BICC or SIP as control plane protocol. In TrFO, the codec capabilities are negotiated by the local and remote end in the call setup phase. As the result of codec negotiation, com-patible codecs are selected in the radio access side and core network. Additionally, a list is created of other commonly supported codecs that are available during the call for a new codec negotiation procedure.

TrFO also provides codec modification and negotiation capability during the call which is required if mobility events or supplementary service invocations result in a change of the used codec.

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TFO and TrFO Guidelines for MSS System Overview of TFO and TrFO in MSS System

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2.3 Benefits for the operatorTrFO and TFO provide the best means to optimize speech quality and speech transmis-sion in the operator network. With TrFO, it is possible to completely remove transcoding from the speech path, because speech encoding and decoding is performed only in the terminals. This not only improves speech quality, but increases the call handling capacity of the MGW because less speech processing is needed.

TFO and TrFO are also useful when the operator network connects to other networks like IMS, fixed VoIP, or other PLMNs. If operators have both 3G and 2G networks with TFO and TrFO, they can offer high definition voice in all parts of their network. This results in better end user satisfaction, as the high quality speech call retains its high quality regardless of end user mobility.

TFO and TrFO key conceptsIn TFO, the basic concept is that a compressed speech codec is negotiated and trans-ported between TFO peers over the user plane. The means of transport, or the tunnel used for the transport in TFO is always an uncompressed 64 kbit/s G.711 codec. The G.711 codec can be selected because of TDM connections, codec negotiation, or as a default codec if the control plane signalling is BICC or SIP.

TFO does not provide bandwidth savings or increase the call handling capacity of the MGW as TrFO does. In the MGW, transcoding resources have to be reserved for a call when TFO is used. Additionally, the transport of the compressed codec inside the 64 kbit/s G.711 codec eliminates the bandwidth saving that results from sending only the compressed codec like in TrFO.

In TFO, control plane entity makes the decision for activating the TFO protocol. The decision can come either from the BSC (if the transcoder is in the BSS), and/or from the MSS (if the transcoder is in the core network). So, for instance, in a payload optimization case where the compressed codec is sent over the backbone and TFO is used between the core and radio network, TFO activation and transcoding and Rate Adaptation Unit (TRAU) codec configurations come from both the BSC and the MSS.

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TFO and TrFO features and concepts

3 TFO and TrFO features and concepts

3.1 Tandem Free (TFO) callTFO is used to enhance speech quality in calls between GSM terminals (2G-2G calls). It can also be used in calls either initiated or terminated by a 3G terminal (User Equip-ment) with the MSS controlling two MGWs which are interconnected through a G.711/TDM line. Additionally, TFO can be applied in cases when the MSS is transiting the call; in such cases the MSS is also controlling two MGWs interconnected through a G.711/TDM line.

When the call enters the speech state, the transcoder units at both sides of the call start to communicate with each other by using an in-band signaling method of sending messages inside the 64-kbit/s speech channel established between them.

This is a standard mechanism performed by the transcoders using in-band signaling. In TFO, the peer transcoders can communicate with each other using bit-robbing signaling inside an established 64 kbit/s channel. If TFO negotiation results in a common com-pressed codec, it is taken into use at both ends and transmitted in TFO frames between the transcoders by overriding part of the 64 kbit/s channel. Since conventional speech (G.711) is also transferred, a quick fallback without noticeable audible effect is provided if the path between the transcoders becomes non-transparent. This can happen, for example, due to tone insertion. TFO is an in-band solution, and the call control system is basically not aware of it, except when the MSS controls the overall TFO by activating it and receiving status information from the MGW.

The following figure illustrates the basic behavior of TFO in a 2G PLMN.

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TFO and TrFO Guidelines for MSS System TFO and TrFO features and concepts

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Figure 1 Inter-MSS MS to MS speech call with default G.711 codec, tandem free operation

The following sections give a summary of some basic concepts in TFO. For more detailed information, see Section Tandem free operation in Feature 1335: Speech Transmission Optimization, Feature Description, in M-release feature documentation.

Location of transcoders in a TFO callThe location of the transcoders that perform TFO negotiation and establishment depends on the network configuration and the used functionalities. In the following, you can read a brief summary of different possibilities for transcoder location in typical TFO calls.

TFO between TRAUs in BSS

TFO is established between the transcoder units (TRAUs) in the BSS. The MSS is not involved in actual TFO negotiation itself, but the MSS still has to support TFO to select correct circuit pool resources towards the BSS, and to disable in-path equipment (IPE) on the user plane for allowing TFO negotiation.

MGW-A MGW-B BSC-BBSC-A

Nb UP

MSS-A

Mc Mc

MSS-B

Nc CP

BSSAP BSSAP

MS-A MS-B

Codec informationexchange

TRANSPARENT COMPRESSED SPEECH CONNECTION

G.711 +AMR-WB

TDM

TrFOG.711 + AMR-WB

Nb UP

RTP

IPv4/v6

UDPAAL2

ATM

G.711 +AMR-WB

TDM

AMR-WB

TDM

Codec

64Kbit/s channelcontaining alsoaccess codec Codec

TFO

1. TC overrides part of 64 Kbit/s channel with access codec2. TFO transparent to MSS3. TC overrides part of 64 Kbit/s channel with access codec


TC-A TC-B

AMR-WB

TDM

A A

1 2 3

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Note that in this case the PCM codec (G.711) has to be used in the backbone. The codecs and their configurations for TFO negotiation are provided by the BSC. TFO acti-vation is either controlled by the BSC when using AMR TFO, or internally by the TRAU in 2G TFO. This configuration is shown in Figure Inter-MSS MS to MS speech call with default G.711 codec, tandem free operation.

TFO between BSS TRAU and MGW

TFO is established between the transcoder unit (TRAU) in the BSS and the transcoder (TC) in the MGW. This configuration is typically used in Payload Optimization when both codec transparency and bandwidth savings are pursued. The BSC makes codec con-figuration and TFO activation for the TRAU. For the TC in the MGW, the MSS carries out the same procedures through the H.248 Mc interface. The compressed codec is used in the backbone to achieve additional bandwidth savings. This kind of configuration is shown in Figure Payload optimization with TFO.

An enhanced version of Payload Optimization is achieved with using the Ater in MGW functionality. When Ater in MGW is used, additional bandwidth can be saved towards the BSC, and no external transcoders (TRAUs) are needed. Otherwise, the functionality is the same as in the standard Payload Optimization case described above, taking into account the fact that the TRAU is integrated into the MGW. This configuration is shown in Figure Payload optimization with Ater in MGW.

TFO negotiation with Immediate TFOOnce the BSC or the MSS made the TFO activation, depending on the transcoder loca-tion, the transcoder receives a list of codecs that the activating party supports and wants to use for inband codec negotiation. The list contains the Locally Used Codec (LUC), the codec selected by the controlling entity, and alternative codecs. The TFO peers exchange their codec lists, and if both peers have the same LUC and there is not any more optimal codec among the alternative ones, they can immediately activate TFO with this codec.

This procedure is called Immediate TFO activation, and it is described in detail in Section Immediate TFO Establishment in 3GPP TS 28.062 Inband Tandem Free Oper-ation (TFO) of speech codecs.

Immediate Codec Type OptimizationIn the TFO negotiation phase, if the LUCs that are selected by the local and the distant side are different, but there is a common codec in the alternative codecs which enables TFO, TFO can be activated between the peers. In this case, either one or both sides need to change their LUC to this common codec. This procedure also applies to cases when the locally used codecs are the same, but they are not the most preferred ones, for example, with AMR-NB as the LUC, but AMR-WB is also supported.

This procedure is called Immediate Codec Type Optimization, and it is described in detail in Chapter Immediate Codec Type Optimization in 3GPP TS 28.062 Inband Tandem Free Operation (TFO) of speech codecs.

Codec Mismatch ResolutionWhen the TFO peers exchange the codec lists in the initial TFO negotiation phase, they only send the LUC and one alternative codec. If this list does not contain common codecs (mismatch), the TFO peers exchange the whole codec list that was given by the TFO activating entity. Now the common codec that can lead to TFO configuration is searched from these complete codec lists.

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This procedure is called Codec Mismatch Resolution, and it is described in detail in Chapter Codec Mismatch Resolution in 3GPP TS 28.062 Inband Tandem Free Opera-tion (TFO) of speech codecs.

Forced Payload CompressionForced Payload Optimization is a Nokia Siemens Networks proprietary functionality, with which the backbone transmission capacity can be minimized. This concept is not directly related to TFO or TrFO, but defines a method where a fixed compressed codec is configured as a default codec for the IP/ATM backbone.

Payload OptimizationPayload optimization is an enhanced version of Forced Payload Compression. Like in TFO, the local and remote MSSs negotiate the common compressed codec in the IP/ATM backbone. Additionally, TFO is used towards the 2G radio network. When TFO is reached with the same compressed codec that is negotiated to the backbone, an optimal situation, called Payload Optimization, is achieved with end to end codec trans-parency and bandwidth savings in the backbone.

For detailed description on payload optimization, see Section Payload optimization with TFO in Feature 1335: Speech Transmission Optimization in MSC Server, Feature Description.

Active/Passive TFOActive/Passive TFO refers to the way how TFO activation is made. 2G TFO can be acti-vated by the MGW or the MSS. In Passive TFO, the 2G TFO functionality is activated by the MGW. In Active TFO, the 2G TFO functionality is activated by the MSS through the H.248 interface. Active TFO is introduced by the AMR TFO and TrFO optimization enhancements functionality.

AMR TFO and TrFO optimization enhancementsIn contrast with earlier releases, where only passive TFO was possible, the AMR TFO and TrFO optimization enhancements functionality introduces Active TFO. In Active TFO, TFO-specific information and TFO activation/deactivation instructions are carried between the MSS and the TRAU/MGW through H.248 signaling, or between the BSC and the MGW through the Ater interface. When a call is set up and the termination and/or codec configuration changes within a context, the MSS checks if TFO activation is necessary. Such cases can include, for example, handover, use of a supplementary services, codec modification, and so on.

The AMR TFO and TrFO optimization enhancements functionality can interwork with SIP-I for basic call establishment cases and for the following supplementary services:

Call forwarding Call waiting Intermediate call Call alternation Call transfer, Call transfer recall Multiparty (MPTY) This functionality enables the operator to provide AMR-WB high quality service for 2G originated calls and codec transparency in calls where SIP-I is used for control plane sig-naling between MSSs instead of BICC. With this functionality, BICC like codec negotia-tion can be used over SIP-I for AMR TFO/TrFO with using the OutOfBand Transcoder

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Control (OoBTC) indicator according to 3GPP TS 23.153. This functionality uses the same AMR TFO/TrFO codec selection logic which has been used for BICC signaling.

For details, see Section Support for 3GPP-defined OoBTC indicator in SDP offer/answer exchanges. For instructions on activating the functionality in the MSS, see Feature 1335: Speech Transmission Optimization, Feature Activation Manual in M-release feature documentation.

With AMR TFO and TrFO optimization enhancements, the Active TFO functionality has to be used.

3.2 Transcoder Free (TrFO) callTrFO provides enhanced speech quality, increased call handling capacity of the MGW, and transmission capacity savings in 3G and IMS/SIP calls. Its functionality is mainly defined in the 3GPP TS 23.153 Out of Band Transcoder Control, Stage 2 specification. The operation is based on codec negotiation and selection performed by the MSS, and user plane operations of the MGW, including user plane protocol handling and auto-matic transcoder removal and insertion, when applicable.

The codec negotiation between the MSSs can be performed either through Bearer Inde-pendent Call Control (BICC) or Session Initiation Protocol for ISUP (SIP-I) signaling. TrFO can interwork with IP Multimedia Subsystem (IMS) through 3GPP SIP signaling. TrFO can interwork with the Fixed Soft Switch (FSS) network through the SIP-I signal-ing.

In BICC, the Application Transport Mechanism (APM) is used to transfer bearer related parameters, such as, speech codecs. In SIP-I and 3GPP SIP signaling, Session Description Protocol (SDP) is used to carry the corresponding codec information.

The corresponding functions are available when SIP-I or 3GPP SIP is used as a signal-ing protocol.

The User Equipment (UE) indicates its codec capabilities during the call setup. The orig-inating MSS creates a proposed list of codecs in priority order. The User Plane Destina-tion (UPD) specific codec preference list is taken into account (if defined) when the UPD level codec support is checked, and when the priority order of the given codecs is deter-mined. For Iu side codecs, the Iu side UPD determines the priority, while for independent part of the SCL, the network side UPD gives the priority order. For more information, see Section UPD configuration

Then the possible intermediate MSS forwards the list, possibly deleting some codecs. The terminating MSS inspects the capabilities of the terminating UE and selects the codec to be used. The UPD specific codec preference list is taken into account (if defined) in the intermediate and terminating MSS as well when codec support is checked. The selected codec is indicated backwards, and the user plane is established, based on the selected codec.

The following figure illustrates this operating principle.

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Figure 2 Transcoder free operation

The following sections give a summary of some basic concepts in TrFO. For more detailed information, see Section Transcoder free operation in Feature 1335: Speech Transmission Optimization, Feature Description.

Transcoder at EdgeIn addition to end-to-end TrFO calls, there are cases where transcoding has to be applied, for example, when the call is terminating to the PSTN network. Even though transcoding can not totally be avoided, it is beneficial to optimize the location of the transcoder. In practice, this means that the compressed speech is transferred as widely as possible, and transcoding is performed at the edge of the PLMN. This naturally leads to transmission capacity savings in the core network. The concept is generally known as Transcoder at Edge and uses the same kind of methods as TrFO.

For more information, see Section Optimization of transcoder location in Feature 1335: Speech Transmission Optimization, Feature Description.

Codec Negotiation (CN)Codec negotiation is performed by the MSSs interacting with each other, with the Radio Network Controllers (RNCs), and with UEs. The idea is to negotiate the common codecs in priority order between the local and the distant end to choose the optimal codec for the call.

For detailed description on codec negotiation, see Feature 1335: Speech Transmission Optimization, Feature Description.

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Codec Modification (CM)Codec Modification usually refers to changing the currently used codec in a call to another codec in the Available Codecs List (ACL). Codec Modification can also refer to situations where a compressed codec has to be changed to an uncompressed codec when a Fax/Modem detection occurs in voice call.

For detailed description on basic codec modification, see Section Basic codec modifica-tion in Feature 1335: Speech Transmission Optimization, Feature Description.

Mid-Call Codec Negotiation (MCCN)The MSS supports mid-call codec negotiation (MCCN) to allow flexible adaptation to codec capability changes during the call. This way the operator can maintain the best speech quality, minimize transcoding, and keep distant nodes up-to-date about the codec capabilities of the initiator node.

For detailed description on mid-call codec negotiation, see Feature 1335: Speech Transmission Optimization, Feature Description.

3.3 TFO and TrFO interworkingTFO and TrFO interworking means additional enhancement for providing complete end-to-end speech transmission optimization in calls where both G.711 and non-G.711 legs are present. Such calls can be, for example, 2G-3G interworking cases where G.711 is used, and thus it is highly probable that TFO is also applied, at least on some legs. TFO and TrFO interworking provides end-to-end codec transparency especially with the AMR-WB codec in both pure 2G, and 2G-3G interworking cases.

For more information, see Section TFO and TrFO interworking in Feature 1335: Speech Transmission Optimization, Feature Description.

3.4 Mobility in TFO/TrFO conceptWhen a relocation or handover occurs, a new user plane connection is established from the anchor MGW towards the UE/MS. Regarding speech quality, it is beneficial to either maintain the currently used codec, or to upgrade to a better one. The main aim is always to avoid the insertion of an extra transcoding stage. To achieve this, the MSS selects a codec for a new call leg based on the currently used codec and on the codec modifica-tion capabilities towards the peer and target system.

If the MSS System supports codec modification, the preferred new codec is the optimal codec supported both by the peer system and the target radio network. Otherwise, the codec used by the peer system is the preferred new codec if it enables more optimal configuration. In a 2G call, a TFO-capable transcoder pool is also preferred when appli-cable.

Inter-system handoverIn inter-system handovers, the optimal codec selection and extra transcoder prevention apply as in normal handovers. If codec transparency cannot be guaranteed, the Transcoder at Edge principle applies, that is, the transcoder is located in the optimal place like in 2G access in a 2G to 3G handover.

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Inter-MSS handoverCodec negotiation is also supported for the handover leg for inter-MSS handovers over the MAP-E interface. With inter-MSS handovers, TrFO can be maintained. Payload opti-mization with TFO is also applicable, provided that the MSS/MSC-B is able to allocate a TFO-capable transcoder.

Handover in setup phaseThe network can be configured so that inter-system handovers occur almost immedi-ately after the call setup initiation. In speech calls, for example, the MSS can recom-mend GSM access for an MS attached 'normally' to UMTS access, which leads to early inter-system handover. When the codec negotiation has already started towards the backbone network (which is probable), code negotiation is based on the original (for example, UMTS access based) codec list. This can lead to selecting a non-ideal codec for the backbone leg.

For more information, see Section Relocations and supplementary services in Feature 1335: Speech Transmission Optimization, Feature Description.

3.5 TFO and TrFO interworking with other servicesCall ForwardingTFO and TrFO do not set any special requirements for early call forwardings because the service is invoked when the outgoing side resource and codecs are not yet reserved. So in early call forwarding, TFO and TrFO functionality is the same as in basic calls.

As for late call forwarding in Call Forwarding on No Reply (CFNR, User Determined User Busy (UDUB), and Call Deflection cases, codec negotiation and TFO activation is made before the invocation of the forwarding service. In this case, the codec selection is renewed and it is based on the codec capabilities of the calling and the forwarded-to parties. After the new codec is selected, a codec modification or negotiation can be required towards the calling party to provide end-to-end codec transparency.

Call TransferSimilar to late call forwarding, a codec modification or new codec negotiation can be required to optimize the codec between the parties involved in the call after the invoca-tion of call transfer.

Call Hold and Intermediate CallWhen the first call is put on hold and an intermediate call is made, the codec selection is analogous to that of a basic MOC call.

Multiparty CallIn multiparty calls, end-to-end codec transparency cannot be achieved because the nature of the multiparty equipment. In multiparty calls, the compressed speech from members is decoded, linearized, and mixed together, and then encoded for individual members according to their currently used codec.

However, it is possible to minimize the amount of transcodings by using codec modifi-cation towards individual members. This can be applied if the codec selected for the call before the multiparty service has led to transcoding in the access interface.

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Lawful interception Lawful interception does not have any influence on the establishment or maintenance of the TFO/TrFO connection. That is ensured for avoiding any audible effect in speech quality or noticeable effect in speech delay to the end users.

Other services With TrFO and the Modem FAX detection functionality, it possible to negotiate a com-patible compressed codec for the call. Codec negotiation is made only if the call type is not known by the transit and terminating MSSs, and the configuration defines to handle the call as a speech call. In other cases, calls are handled as data or fax call.

If a Modem/Fax signal is detected, the compressed codec can be modified to the 64 kbit/s G.711 codec suitable for Modem/Fax transmission.

G.711 with 20 and 10 ms packetization periods3GPP has standardized G.711 with 20 ms packetization period for Nb/IP backbone in Rel-7 with BICC signaling (in 3GPP TS 29.414 Core network Nb data transport and transport signalling, Release 7). This also affects TrFO so that if codec negotiation leads to G.711 codec on Nb (BICC) interface, the 20 ms packetization period can be used. Previously, only standard 5 ms could be used.

The MSS System also supports 10 ms packetization period for the G.711 codec. 10 ms packetization is defined by IETF and required, for example, in national IP interconnect, and it is supported by different soft switching platforms which are widely used in fixed networks today. This functionality works only with SIP and SIP-I call control protocols when user plane traffic is transferred directly on top of RTP.

3.6 Charging and statistics with TFO and TrFOChargingIn charging, the used codecs are shown in the MOC, MTC, and FORW CDRs.

StatisticsMSC Server

In TrFO measurements, the measured object is the MSC Server and the information provided consists of TrFO accomplishment in calls as follows:

Part time TrFOTrFO was achieved during the call, but not for the whole duration of the call.

Full time TrFOTrFO was achieved for the whole duration of the call.

TrFO Candidate failedThe call could have reached TrFO (there was a possibility for it), but it is not a TrFO call.This can happen, for example, if a 3G-3G TrFO call is being established and there is a mismatch in the configuration of the RNCs, no common codec can be found for the call, and a transcoder has to be inserted. The counter is always updated on MSS level, that is, the MSS checks if there is a mismatch of codecs on the ingress and egress sides in a TrFO candidate call. If this is the case, the MSS increments the counter.

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TrFO non-candidateThe call has a G.711 codec reserved in the call path somewhere, therefore, it is not possible to achieve TrFO.

Further optional counters are available for Circuit Group measurements:

TFO activation on incoming circuit group TFO activation on outgoing circuit group Successful TFO (TFO status event is ON) on incoming circuit group Successful TFO (TFO status event is ON) on outgoing circuit group Unsuccessful TFO (TFO status event is OFF) on incoming circuit group Unsuccessful TFO (TFO status event is OFF) on outgoing circuit group Optimal Codec event on incoming circuit group Optimal Codec event on outgoing circuit group Attempted codec modifications Codec negotiation attempts Successful codec modifications Successful codec negotiations Calls with full time TRFO and WB-AMR codec Restarts of data provider in the signaling unit or of some signaling units Calls not using transcoder resources during the whole call Calls not to use transcoder resources by the nature of the call, but for some reason

transcoding is needed Calls using transcoder resources by the nature of the call Calls not using transcoder resources for some time during the callThe measurements can be managed by the T2 - Measurement Handling MML command group, and the same principles are used as in UPD measurements.

For more information on UPD measurement reports, see Section UPD Measurement report (384/180H) in NSS Statistics, Reports in M-release product documentation.

MGW

The MGW provides statistics about TFO and TrFO usage. For more detailed informa-tion, see MGW Counters - Resource and Service Part in U-release product documenta-tion.

Periodic measurements in MGW can be managed either by using the Measurement Handling (T2) MML command group, or NE Measurement Explorer GUI in NEMU. The measurement result can be viewed from the NEMU database using NE Measurement Explorer GUI. All data of these measurements are also transferred to NetAct where it can be viewed using the NetAct reporting tools. For more information about measure-ment management, see Performance Management in MGW in U-release product doc-umentation.

3.7 ComplianceBecause TrFO and TFO are system level features and require support from both the core and radio networks, it is essential that the features are well standardized to avoid Interoperability Testing (IOT) problems in multivendor environments.

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The Nokia Siemens Networks TFO and TrFO implementation complies to the following main 3GPP TFO and TrFO specifications:

3GPP TS 23.153 v5.8.0 Out of band transcoder control; Stage 2 3GPP TS 28.062 v6.0.0 Inband Tandem Free Operation (TFO) of speech codecsThere is a multitude of other 3GPP specifications that affect TrFO and TFO. For details on these specifications, see the References chapter in the above listed specifications. The codecs that are applicable with TrFO and TFO are also standardized in detail in further 3GPP, ITU-T, and IETF specifications.

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4 TFO and TrFO architecture guidelinesThe following section presents major examples of architecture alternatives that can be built in speech transmission optimized networks. The section also includes guidelines for architecture selection and successful optimization planning.

4.1 Network architecture overviewThere are several high level architecture possibilities for implementing TFO and TrFO in operator networks. The most suitable architecture for a specific operator network depends on the needs and aspirations of the operator. In other words, it depends on what the key issue is for the operator, for example, enhanced speech quality, transmis-sion optimization, or both of them.

This section describes the main alternatives with their advantages and disadvantages, to provide some guidelines for architecture selection.

TrFO in 3G networkIn this alternative, TrFO is used in a 3G network to provide both transmission optimiza-tion, enhanced speech quality, and MGW transcoding resources savings, as presented in the figure below.

Figure 3 TrFO in 3G

In this network architecture, TrFO is supported at system level, which means that both the core network and the radio access network support TrFO. The call is end-to-end codec transparent. Optimal speech quality and bandwidth savings are achieved in the

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core network by transporting only the compressed codec without any extra overhead. Additionally, the capacity of the MGW is optimally used because no transcoder resources have to reserved for the call.

In this typical TrFO deployment, the configuration and the functionality is straightforward as long as the network elements have a homogeneous configuration for the supported codecs and for the TrFO feature itself. In such cases, the setup of an end-to-end codec transparent call is made after an initial codec negotiation, and subsequent mobility events like relocations and supplementary services invocations do not break the TrFO.

If TrFO is introduced to a network where codec capabilities and TrFO support vary, the risk for tandem transcoding increases. This is particularly important when high definition voice, that is, AMR-WB, is introduced into the network. In this case, it is important to understand that the basic setup phase for TrFO capabilities are not enough. During the call, mobility events like relocations can result in a situation when the selected codec cannot be sustained, and end-to-end codec modifications are needed for optimizing the call configuration. This means that the core network has to identify the situation and trigger proper modification procedures to the call to obtain the best possible speech quality without jeopardizing bandwidth savings. Both the core and radio access network have to be able to carry out codec modification.

g In theMSS System, TrFO and AMR-WB codec are also supported with CS voice over I-HSPA networks in the same way as over standard 3G networks. At system level, the available functionality set depends on the corresponding I-BTS support.

TFO in 2G networkTandem Free Operation (TFO) provides the best means for optimizing speech quality in 2G networks.

The TFO is a long established feature in 2G networks, and it has been enhanced during the past years. In practice, this means that TFO is sometimes deployed only for GSM codecs, and TFO itself is not controlled by the MSC Server (MSS). With the introduction of AMR codecs, new requirements emerged for TFO, and the old 2G TFO has been further enhanced with AMR TFO support. The control of TFO has been moved to the MSS to provide TFO and TrFO interworking. The new TFO concept covering both old 2G TFO and AMR TFO is called AMR TFO and TrFO optimization enhancements.

For illustration on traditional 2G environment with TFO in use, see Figure Inter-MSS MS to MS speech call with default codec, tandem free operation.

In this network architecture, TFO is used between the transcoders (TC) located in the BSS. The TFO spans over the core network and is practically invisible to the MSS, except that the MSS still controls the A-interface circuit pool selection. This configuration requires that the MGW can remove in-path equipment (IPE) from the speech path when it encounters TFO messages. TFO support for GSM and AMR codecs depends on the capabilities of the BSS and the transcoder.

Although this configuration provides optimal speech quality with end-to-end codec trans-parency, it is not suited for bandwidth savings because the bandwidth of the core network has to be reserved according to the capacity of the PCM codec (G.711).

This basic TFO scenario has been enhanced to provide additional bandwidth savings by introducing the Payload Optimization (PO), as illustrated in the figure below.

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Figure 4 Payload optimization with TFO

In the Payload Optimization concept, TFO is used only in the parts of the call connection where transporting the compressed codec is not possible, like in A-interface - TDM con-nection. In the backbone, the compressed codec can be transported without the addi-tional overhead of the G.711 codec used in the A-interface. Payload Optimization can be used with both 2G TFO and AMR TFO and TrFO optimization enhancements. With 2G TFO, end-to-end codec transparency can be provided only for GSM codecs.

Payload Optimization for AMR codecs requires the use of AMR TFO. The transmission optimization method for the backbone can be either default codec or codec negotia-tion. The default codec method is suited for PO with 2G TFO when either the Full Rate (FR) or the Enhanced Full Rate (EFR) codec is used in the call. For PO with AMR TFO, only the codec negotiation method can be used, as the AMR codec contains several modes that are not supported with the default codec method. Generally, it is recom-mended that the codec negotiation method is used as it provides the best possibility for reaching codec transparency.

To further enhance the Payload Optimization concept, Nokia Siemens Networks offers the Ater in MGW feature which improves capacity even further. When using the Ater in MGW feature, only the compressed codec is transported between the BSS and the MGW, and TFO is used inside the MGW, as illustrated in the figure below.


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Figure 5 Payload optimization with Ater in MGW

TFO in 3G network and in PLMN interconnectionUsing TFO is not limited to 2G. The AMR TFO and TrFO optimization enhancements functionality can also be very useful in cases where the operator backbone has not yet been migrated to IP/ATM, using TDM still. Operators can offer codec transparency and high definition voice with AMR-WB the final migration to IP/ATM.

Inter-PLMN connections still use mostly TDM, and codec transparency with codec nego-tiation cannot be achieved. With AMR TFO and TrFO optimization enhancements, full codec transparency for both narrowband and wideband codecs can be provided between PLMNs. Instead of TDM, SIP-I or BICC with the G.711 PCM codec can also be used together with AMR TFO and TrFO optimization enhancements in PLMN intercon-nections.

Figure 6 TFO between PLMNs, with TDM or G.711 (SIP-I, BICC) interconnection

TFO and TrFO interworkingTo achieve optimal bandwidth usage and codec transparency, you need both TFO and TrFO, as well as their interworking. With TFO-TrFO interworking, codec configurations can be negotiated end-to-end when both TFO and TrFO are used in the call. It is also possible to modify the used codec subsequently, due to, for example, mobility events or


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supplementary services. The following figure illustrates a typical TFO-TrFO interworking case in a codec transparent call between a 2G and a 3G subscriber.

Figure 7 TFO-TrFO interworking (2G-3G call)

When TFO and TrFO interworking is used, the MSS controls the TFO activation and performs codec negotiation/modification. Codec negotiation/modification is made both in-band over the TFO connection, and out-of-band over the BICC or SIP-I connection.

If end to end codec transparency cannot be achieved, TFO-TrFO interworking usually results in the Transcoder at Edge configuration where transcoding is made only at one side of the call.

TrFO and TFO codec handling with A over IPThe introduction of A over IP (AoIP) support in the MSS provides an opportunity for the operator to use TrFO for 2G calls, as illustrated by Figure Example of 2G TrFO with AoIP. This provides potential savings of transmission resources compared to TFO while still providing enhanced speech quality. Both the basic TFO/TrFO functionality provided by Feature 1335 and the improved TrFO and TFO mechanisms provided by the "AMR TFO and TrFO optimization enhancements" functionality are impacted by this feature.

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Figure 8 Example of 2G TrFO with AoIP

The AoIP support functionality provided for the MSS allows the transcoding functions to be contained either in the MGW or in the BSS. However, with TC in the BSS, TFO or TrFO/TFO interworking is not possible in MSS SR4.0; which means codec transparency and HD voice quality cannot be reached.

For more details on the MSS implementation of A over IP, see Feature 1895: A over IP (AoIP) Support in the MSC Server, Feature Description and Feature 1335: Speech Transmission Optimization, Feature Description in M-release feature documentation. For activation instructions, see Feature 1335: Speech Transmission Optimization, Feature Activation Manual. All these documents can be found in M-release feature doc-umentation.

For more information on AoIP implementation and integration in the MGW, see Func-tional Description for Nokia Siemens Networks Multimedia Gateway and Integrating MGW into the MSC Server System in U-release product documentation.


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TFO and TrFO Guidelines for MSS System TFO and TrFO configuration guidelines

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5 TFO and TrFO configuration guidelinesTFO and TrFO configuration at system level entails the following areas:

MSS data configurationThe MSS configuration contains UPD, MSS, RNC, and BSS configuration data.

MGW data configuration Configuration of the User Plane (UPD configuration) Licences in the MSS, MGW, RNC, and the BSS Configuration of the radio access network (RAN configuration)The following figure illustrates TFO-TrFO configuration at network level.

Figure 9 TFO-TrFO configuration at network level

There are many issues to take into account when deploying TFO and TrFO. First of all, you have to check the maturity of the network for the TFO and TrFO features.

5.1 Network support for TFO and TrFORNC support for TrFOWhen you deploy TrFO in the RNC, you have to consider the following issues:

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Do RNCs fully support the standard TrFO, or do they provide only basic call setup functionality?In other words, are codec modifications supported between all AMR codecs and configurations, or only between narrowband and wideband?

What are the supported codec configurations? Are they compatible with the corre-sponding configurations on the core side and in 2G when intersystem calls are made? For instance, if the RNC and the BSS support narrowband AMR, but the configura-tion differs so that instead of 7.4 kbit/s, the RNC supports 7.95 kbit/s, the call needs transcoding because the codecs are not TrFO/TFO compatible.

If Iu over ATM is used, check if CS-1, AAL2, or CS-2 AAL2 type of modification is used. With Iu over IP, only CS-2 type modification can be used. Before you start the configuration, make sure that proper licences are installed and activated.

In I-HSPA networks, I-BTSs also play the role of RNCs. TrFO and AMR-WB codec can be used for CS voice calls in the same way as in standard 3G networks.

BSS support for TFOIn many cases, 2G networks consist of old BTSs and transcoders that either cannot be upgraded or their upgrade is not feasible, for example, regarding capital expenditure. In such cases, operators can choose not to use TFO at all in 2G, or fall back on the old 2G TFO solution. In that case, they also have to consider that, for example, high definition voice with AMR-WB cannot be used in 2G. This clearly affects end user voice quality if inter-system handovers happen in the network. The Nokia Siemens Networks A-ter solution can be an option for such cases, too, because with A-ter, TRAUs are not needed, and the transcoding is made in the MGW.

When you deploy the AMR TFO in the BSS, you have to consider the following aspects:

AMR TFO supported codecsAMR TFO supported codecs and their configuration have to match both in the BSC and in the MSS/MGW.

Circuit pool configurationsIf you want to prevent circuit pool switching, configure circuit pools so that the codecs between which there are changes are located in the same pool. Make sure that the pool configurations are identical in the MSS and in the BSC. Note that if A-ter is used, circuit pools have to be configured for the MGW as well.

AMR TFO capability of the BSSIs AMR TFO supported for both narrowband and wideband AMR, or only for one of them? Should the call be started with narrowband AMR, to minimize downgrades from wideband to narrowband? In the migration phase to wideband speech, most of the calls end up narrowband if the receiving terminal does not support wideband speech. So, it can be optimal to start the call with narrowband codec.

AMR TFO deploymentIs AMR TFO required for all AMR capable terminals, or only for those which support wideband speech (AMR-WB)?

LicencesBefore you can do any configuration, you have to install and activate proper licences for AMR TFO and AMR-WB.

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BSS support for TrFO (with AoIP)With AoIP support implemented in the BSS, TrFO can be reached throughout the mobile network with using AMR-WB codec end-to-end. For this, transcoder have to reside in MGWs.

In this configuration, there are IP connections between the BSC and the MGW for the user plane of A-interface, and between the BSC and the MSS for the control plane of A-interface. In the control plane, SIGTRAN signaling is used, while the user plane uses RTP payload formats for different speech codecs (GSM HR, GSM FR, GSM EFR, AMR and WB-AMR) and CS data/fax.

MSS System support for TFO & TrFOthe MSS System has an important role between the radio access and other external interfaces. The MSS System helps optimize the call configuration, so that operators can achieve the best possible speech quality and make savings in transmission costs. Ver-satile MSS System support for TFO and TrFO facilitates the optimization in the network when radio accesses have varying capabilities. Codec mismatches and location of transcoders can be handled effectively if core network codec modification/negotiation and codec support is in order.

When you are planning to deploy the TFO and TrFO features in the MSS System, you have to consider the following issues:

Are both TFO and TrFO used at the same? (TFO & TrFO interworking) What level of TFO is supported, that is, none, 2G TFO, or AMR TFO and TrFO opti-

mization enhancements? Is codec transparency required at system level for all calls, or only for 2G-2G and

3G-3G calls? If HD voice with AMR-WB is deployed, what level of support is required: system

level, or only in 3G? System level support requires TFO & TrFO interworking, and BSS upgrade for AMR TFO and AMR-WB.

Interworking towards RNCs: RNC supported codecs, RNC-side UPD configuration Interworking with BSSs: circuit pool configuration (MSS andMGW); A-interface or

Ater used towards the BSS; AMR codec configurations per BSC Interworking with other external interfaces: SIP (profile A), SIP-I, PSTN, voice appli-

cation platforms, and so on Interworking between MSSs: UPD configuration for speech transmission method

and supported codecs (optional) Licences

Before you can do any configuration, you have to install and activate proper licences for AMR TFO and TrFO optimization enhancements, TrFO and AMR-WB.

5.2 LicencesBefore you configure the network for TFO and TrFO, you have to install and activate proper licenses.

MSS licensesFor the MSS, the basic features for TFO and TrFO are as follows:

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N.2332 TrFO and TFO in MSC ServerN.2332 provides the basic TrFO and TFO functionality. With N.2332, 2G TFO for GSM codecs is supported, and for TrFO, the basic call setup is included, but without the optimization features.

L./C.1422 AMR TFO and TrFO optimization enhancementsL.1422 provides the TFO enhancement for AMR codecs and TrFO optimization including TFO and TrFO interworking.Note that L.1422 is not supported in the integrated MSS or in the DX MSC.

There are optional items that provide additional enhancements:

C.1417 TrFO Codec Negotiation Measurement N.3399 AMR-WB Information in CDR C.3390 AMR-WB Codec in MSS L./C.4247 MSS A over IP with TC in MGW L.4264 - MSS A over IP with TC in BSS L./C.4172 AMR-WB Subscription

Requires L.3390 AMR-WB Codec in MSS as prerequisite. L./C.4174 WB AMR activation on IMEI control L./C.4176 AMR TFO only for AMR-WB terminals

This item provides the possibility to use new transcoders only with terminals that support AMR-WB.

L./C.4179 IMSI range/PLMN based control for WB AMR

g L./C.4172, L./C.4174, L./C.4176, and L./C.4179 require C.3390 AMR-WB Codec in MSS as prerequisite.For overview on MSS licences, see Software Licencing, Functional Description in M-release product documentation. For more information on the particular licences, see Software Sales Items for M-releases in M-release feature documentation.

MGW licensesThe following table lists basic, related, and optional licences for activating TFO/TrFO in the MGW:

Licence code Feature code

Feature Licence type

TFO/TrFO basic licences

3GNLIC0010 815 MGW VoIP codec G.729A/B capacity

3GNLIC0011 816 MGW VoIP codec G.723.1 capacity

3GNLIC0012 814 MGW VoIP codec iLBC capacity

3GNLIC0023 798 MGW AMR TFO capacity

3GNLIC0025 1036 MGW HR codec support for Ater capacity

3GNLIC0033 802 MGW TrFO capacity

3GNLIC0035 803 MGW AMR-WB capacity

3GNLIC0042 799 MGW 2G TFO capacity

Table 2 TFO and TrFO licences in MGW

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3GNLIC0033, 3GNLIC0042 and 3GNLIC0035 are used with MGW U4.0 or later releases, and they provide licence based feature control.

3GNLIC0023 facilitates TFO with AMR multimode codecs.

3GNLIC0039 is especially needed when SIP-I is used on the Nc feature. Without this feature, the G.711 codec has to be used on Nb (SIP-I) interface to enable DTMF delivery through the IP backbone.

With 3GNLIC0052, in the IP backbone, where G.711 is used because of certain reason, the bandwidth consumption can be decreased by using the 20 ms packetization period instead of 10 ms. However, if required, 10 ms packetization can also be used with 3GNLIC0065, for example, towards fixed softswitches.

The 3GNLIC0057 port capacity licence also applies to cases when the TC is located in the BSS.

For an overview on licence handling in the MGW, see Licence-based Feature Manage-ment in U-release product documentation. For overview on MGW licenses, see Config-uration Data Management in MGW in U-release product documentation.

RAN licensesFor using TFO and TrFO in the radio access network, activate Feature RAN134: Support for Tandem/Transcoder Free Operation.

RNC/I-BTS TrFO support means that Iu UP version 2 has to be supported. Additionally, the RNC has be able to accept Rate Control frames from the core network if multimode AMR is used in the call, and the distant side uses different modes depending on traffic conditions.

If AMR-NB changes to AMR-WB in the network, codec modification between AMR-NB and AMR-WB has to be supported to prevent NB-WB transcoding.

MGW port capacity licenses of interfaces where TFO/TrFO can be used

3GNLIC0027 1116 MGW Iu ATM IP 3G port capacity capacity

3GNLIC0028 1115 MGW Nb IP backbone port capacity capacity

3GNLIC0029 1114 MGW Mb IP access port capacity capacity

3GNLIC0030 756 MGW Ater interface capacity

3GNLIC0043 1113 MGW Iu IP 3G port capacity capacity

Optional licences related to TFO/TrFO

3GNLIC0035 803 MGW AMR WB capacity

3GNLIC0039 846 MGW DTMF codec capacity

3GNLIC0041 804 MGW FAX Modem Detection ON/OFF

3GNLIC0050 1245 MGW Ater circuit pools 28 and 32 capacity

3GNLIC0052 1065 MGW G.711 20 ms in Nb interface ON/OFF

3GNLIC0057 1334 MGW A over IP port capacity with TC in MGW

capacity

3GNLIC0065 1680 MGW G711 10 ms with SIP ON/OFF

Table 2 TFO and TrFO licences in MGW (Cont.)

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For details on RAN licence handling, see Licence Management Principles in the WCDMA RAN System Library.

BSS licensesYou can enable or disable the Wideband AMR and TFO for AMR features on BSC level. The related license keys are as follows:

BSS20960 Wideband AMR BSS21118 Tandem free operation for AMR

This licence provides TFO functionality for narrowband AMR only. BSS21312 Wideband AMR capacity license

With this licence, you can extend the capacity limit of 100 WB-AMR calls for each BSC.

BSS21412 A over IP TrialWith this licence, you can activate AoIP support in the BSS.

For details on licence handling in the BSS, see Licensing in BSC in GSM/EDGE BSS product documentation.

5.3 MSS configurationOnce you have installed and activated the licences, you continue with the configuration of the TFO and TrFO functionalities. You have to set the general parameters (FIFILE, PRFILE) that affect TFO and TrFO functionalities to the desired values depending on the network in question. A good way to start is to use the default values suggested by the vendor. For available parameters, see Section MSS parameters.

For information on installing licences in the MSS, the MGW, and the radio network, see the following documents:

Software Licencing, Functional Description in M-release product documentation Licence-based Feature Management in U-release product documentation Licensing in BSC in GSM/EDGE BSS product documentation Licence Management Principles in the WCDMA RAN System LibraryRNC configuration dataThe RNC codec capabilities include the following information:

RNC supported AMR speech codec mode countThis means how many modes can simultaneously be selected for a RAB connec-tion.

RNC supported speech codecsThis indicates codecs which are supported by the RNC.

RNC supported AMR speech codec mode setsThis indicates the WB configuration codecs and NB mode sets, which are allowed toward the RNC.

RNC PARAMETER SET version R4, which is used with TrFOFor more information on RNC configuration data, see Cellular Radio Network Manage-ment, Operating Instructions and Radio Network Controller Parameter Handling in MSS, E2 Command Group, Command Reference Manual in M-release product documenta-tion.

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Optionally, emergency calls can be configured to use either early or late RAB assign-ment, and narrowband codec. For more information on used parameters, see Section Summary of TFO and TrFO parameters.

The General Codec Preference File (CDGFIL) packetized by the MSS is used tell the codec priority on an MSS basis. If the RNC specific codec preference is desired, the codecs can be configured also to the RNC side UPD. For details, see Section UPD con-figuration.

BSS specific configurationOne of the most important and error prone areas is the configuration of circuit pools towards the BSS. The following list provides a few examples of the several issues that you have to consider about circuit pool configuration:

If transcoders (TRAUs) in the network have differing capabilities, and the you want to upgrade them gradually, TRAUs have to be grouped into different circuit pools.

BSC and Transcoder vendor and multivendor environment.Some BSCs are not able to fully support circuit pool switching so it is important to have most used codecs in the same circuit pool to prevent pool switching.

Some vendors have TRAU blades that support AMR TFO for AMR-NB and AMR-WB, and other blades that support AMR TFO only for AMR-NB. So, these blades have to be grouped to their own circuit groups.

When AMR TFO is deployed, you can choose to allow its usage either for all AMR supporting terminals, or only for those that support AMR-WB. If all AMR capable ter-minals are supported, the initial investment is higher because most of the terminals nowadays support AMR-NB but not AMR-WB. If you choose gradual deployment with AMR TFO and AMR-WB, check if circuit pool configuration solves this issue. If not, you need to install Feature 1690: Support for Wideband AMR Codec in MSS. For more information, see the corresponding feature description in M-release feature documentation.

The following examples aim at clarifying the importance of circuit pool configuration.

Example: Different TRAUs for AMR TFO support only for AMR-NB, and AMR TFO support for AMR-WB and AMR-NB

Figure 10 TRAUs with different AMR TFO support

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In the figure above, there are four TRAUs in the solution of the BSS vendor. One of the TRAUs is fully upgraded (both in HW and SW) to support AMR TFO for all codecs (WB, NB, GSM). Another TRAU has software update and supports AMR TFO for AMR-NB and GSM codecs. There are two old TRAUs that have not been updated and they can have TFO support for 2G only, or no TFO support at all.

For this setup, the optimal circuit pool configuration is that TRAU resource is hunted from pool A for AMR-WB capable terminals.

For terminals that support AMR-NB and GSM codecs, the resource is hunted first from pool B, and if these resources are all used up, pool A is used. If pool A is not needed with subsequent hunting, it doesn't have to contain AMR-NB, and the BSC has to support pool switching in case a codec modification from AMR-WB to AMR-NB takes place. If pool switching is not supported, the 'AMR TFO support only for AMR-WB capable terminals functionality is needed. For more information, see Feature 1690: Support for Wideband AMR Codec in MSS, Feature Activation Manual in M-release feature documentation.

For terminals that support GSM codecs, the circuit is hunted from pool D.

If all TFO capable circuits are used up, the circuit is hunted from circuit pool C.

The following example shows a real life configuration:

A = CP 39 with TFO B = CP 27 with TFO C = CP 27 without TFO D = CP 7 with TFOExample: New AMR-NB/WB and AMR TFO capable TRAUs with old TRAUs and A-ter interface

Figure 11 New TRAUs coexisting with old TRAUs and Ater interface

In the figure above, both the A- and the Ater interfaces are used at the same time. In this case, you have to consider aspects:

New TRAUs support TFO for AMR NB/WB and GSM codecs. Old TRAUs support TFO only for GSM codecs and AMR-NB in non-TFO cases. The BSC does not support circuit pool switching for changing the codec, for example, between AMR-NB and AMR-WB.

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A-ter interface with transcoder in the MGW is concurrently used with external TRAUs.

The first things you have to decide about A-interface circuit pooling is how you want to migrate to AMR TFO. If you offer AMR TFO for both AMR-NB and AMR-WB capable terminals, the configuration is straightforward: the new TRAUs are configured to their own circuit pool, for example, E = CP 39. AMR calls use pool E, and non-AMR calls use pool G. If CP E becomes congested, pool F with no TFO can be offered for AMR capable terminals.

The situation is more complicated if you want to gradually migrate to AMR TFO, offer first, for example, AMR TFO for AMR-WB capable terminals, and let the old AMR-NB only terminals use either a limited amount of new TFO capable TRAUs or only old non-TFO capable TRAUs. The benefit of gradual migration is that HD voice can be intro-duced to the GSM network with investment on new TRAUs, and the number of new TRAUs is in direct proportion to the amount of AMR-WB capable terminals in the network.

Technically, this cannot be accomplished with only circuit pool configuration, because a pure AMR-WB capable circuit pool is not really appropriate towards a BSC that does not support circuit pool switching, that is, codec change from AMR-WB to AMR-NB is not possible. However, by deploying the AMR TFO support only for AMR-WB capable ter-minals functionality, you can invest in new TRAU resources according to the increasing amount of HD voice terminal penetration in the network. With this functionality, you can make sure that TRAU resources are available for AMR-WB terminals. Additionally, for the AMR-NB capable terminals, AMR TFO can be gradually deployed if you want so.

Figure New TRAUs coexisting with old TRAUs and Ater interface also shows the Ater interface which provides additional transmission savings and capacity towards the BSC. Using Ater interface, the transcoder is in the MGW, and external TRAUs are not used. In this case, the circuit pool configuration is a bit more complicated because the identical pools need to be configured in three places, that is, in the MSS, the BSC, and the MGW. Identical circuit pool configuration is needed only in the MSS and the BSC. Regarding the MSS, Ater circuits look the same as A-interface circuits. MGW circuit pooling is used for providing optimal DSP resources for the call and avoiding unnecessary DSP service changes. For example, if Ater is used with AMR TFO and AMR-WB, the circuits are con-figured to CP H = 37.

In releases before SR3.2/M14.4, the circuit pool selection is that 'Priority on TFO' hunting preference is used on the originating side, and 'Priority on Codec' is used on the terminating side. In SR3.2/M14.4, this is streamlined so that both the originating and the terminating sides use 'Priority on TFO'. For explanation on these terms, see below:

Priority on Codec A hunting order where circuits are hunted from the TFO capable pool for the first TFO capable codec in channel type codec lists. If there is no success, circuits are hunted from non-TFO capable pools for the same codec (except for AMR-WB). If there is still no free circuit avail-able, the next codec is selected, and circuits are hunted normally for the codec from non-TFO pools.

Priority on TFO A hunting order where circuits are hunted first from TFO capable pools for the first TFO capable codec in channel type codec lists. If there is no success, the next TFO capable codecs are selected, and circuits are hunted for them from TFO capable pools. If there is still no free circuit available, the codec list is restarted from the beginning and

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circuits from non-TFO capable pools are hunted for the codecs (except for AMR-WB).

For details on configuring the Ater interface in the MGW, and on configuring transcoders for the Ater interface between the BSC and the MGW, see Section Configuring the transcoder for the Ater interface between BSC and MGW in Integrating Multimedia Gateway into the MSS System in U-release product documentation.

For handling the BSC, see Cellular Network Controller Handling, ED Command Group, Command Reference Manual in M-release product documentation.

Configuring BSC codec capabilitiesIn addition to circuit pools, in the BSS you have to configure AMR codec capabilities for each BSC. You can define either AMR-NB or AMR-WB codec and the corresponding codec configuration mode set.

For creating, modifying and interrogating the mode sets of AMR codecs, see General RNW Parameter Handling in MSS, E9 Command Group, Command Reference Manual in M-release product documentation. For attaching the created mode sets to the BSC, see Cellular Network Controller Handling, ED Command Group, Command Reference Manual and Radio Network Controller Parameter Handling in MSS, E2 Command Group, Command Reference Manual in M-release product documentation.

UPD configurationIn the MSS System, the user plane and the control plane are separated. The control plane is handled by the MSS, and the user plane is handled by one or several MGWs. MGWs are further divided into groups that have common properties like connectivity towards other network elements and used bearer technology. These groups are called User Plane Destinations (UPDs) which are defined in the scope of one MSC Server. Based on user plane analyses, UPDs are further divided into preceding and succeeding UPDs.

For detailed description on User Plane Handling and UPDs, see User Plane Routing, Functional Description in M-release product documentation.

The configuration steps for creating MGWs, UPDs and UP analysis are as follows:

1. Create MGWs in the MGW database of the controlling MSS with the JGC and JGM commands.

2. Create UPDs in the Topology database with the JFC and JFM commands.3. Add the MGWs to the UPDs.

Check with the JGI command if the MGW exists in the MGW database, so that it can be controlled by the MSS.

4. Create User Plane Analyses. Check with the JUI command if the given UPD, the result of the analysis, is in the Topology database or not.

Regarding TFO/TrFO, UPDs not only contain MGWs with common properties, but they also indicate other capabilities like:

Whether default codec or codec negotiation is to be used with the connection (mutu-ally exclusive)Default codec or codec negotiation settings are valid only in network side UPDs. In access side UPDs, these are not relevant parameters.

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Level of codec modification (CM) and mid-call codec negotiation (MCCN) supportMCCN is relevant only in network side UPDs, while CM is relevant for network and access side UPDs as well.

Optional codec preference list which contains the supported codecs for the UPD. In some cases, for example, RNC MOC call, the codec preference list also acts as a priority list when selecting the codecs towards the terminating side of the call.

Example: 3G-3G inter-MSS callThe following figure shows an example of an 3G to 3G TrFO call when the user equip-ments are under different MSSs.

Figure 12 3G-3G inter-MSS call

There are four different UPDs in the call configuration, and their purposes are as follows:

UPD1 This is the incoming UPD (Preceding UPD) for MSS1 from RNC1, and it is configured to the RNC1 data. This UPD contains MGW1, and it has the following additional properties:

If the codec preference list is configured to UPD1, the list is used in MOC calls as codec priority list, and it overrides the codec priority list of MSS1.

Codec Modification information indicating whether RNC1 supports codec modification or not. Codec modification towards the RNC usually means modification between AMR-NB and AMR-WB codecs.

UPD2 This is the outgoing UPD (Succeeding UPD) for the MSS1. UPD can be defined with the help of the UPD route data received from the digit anal-ysis. This UPD contains MGW1, and it has the following additional prop-erties:

If the codec preference list is configured to UPD2, the list is used as a capability list when creating the Supported Codec List (SCL). The SCL is used in codec negotiation with MSS2.

Codec Modification (CM) information indicating that CM is sup-ported with this UPD.

Codec Negotiation (CN) information indicating that CN is used in the call establishment towards MSS2. This is not tied to the TrFO licence, but it is mandatory when TrFO is used.

RNC1 MGW1 MGW2

MSS2MSS1

Mc Mc

Nc

UPD2

UPD3

UPD1

UPD4

Iu Nb

RNC2 UE-BUE-A

IuIP/ATM

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Default Codec (DC) which is mutually exclusive with Codec Negoti-ation (CN) information. The default codec can be used when only transmission savings are wanted over the backbone, or if 2G Payload Optimization/Forced Payload Compression is used. With TrFO, CN has to be used.

MCCN capability information which indicates how mid-call codec negotiation is supported towards MSS2. You are recommended to use value 'Start/Accept'.

Trunk capability parameter, which means that in call cases where BICC, or SIP-T control plane signaling is used, the bearer type is IP, and the used codec is G.711. In these cases, no Nb UP framing protocol is used, and the packetization period is 20 ms. This UP interface is called Nb and it is proprietary to Nokia Siemens Net-works.

UPD3 This is the incoming UPD (Preceding UPD) for MSS2. The UPDR value is received from the Circuit Group (CGR) data, which can be mapped to UPD with the help of User Plane Analysis. This UPD contains MGW2, and it has the following additional properties:

If the codec preference list is configured to UPD3, the list is used as a capability list to filter SCL codecs when creating, for example, Available Codec List (ACL). The ACL is used in codec negotiation with MSS1.

Codec modification, codec negotiation, and MCCN capability infor-mationThis information should be set similar to UPD2.

The parameter settings of UPD2 and UPD3 have to be in line with each other.

UPD4 This is the outgoing UPD (Succeeding UPD)

MSS_TFO and TrFO Guidelines.pdf

Documents

Transcript of MSS_TFO and TrFO Guidelines.pdf