2 General Approach

08.603GPPIn-band control of remote transcoders and rate adaptors for Enhanced Full Rate (EFR) and full rate traffic channelsTS

When the transcoders/rate adaptors are positioned remote to the BTS, the information between the Channel Codec Unit (CCU) and the remote Transcoder/Rate Adaptor Unit (TRAU) is transferred in frames with a fixed length of 320 bits (20 ms). In the present document, these frames are denoted "TRAU frames". Within these frames, both the speech/data and the TRAU associated control signals are transferred.

The Abis interface should be the same if the transcoder is positioned 1) at the MSC site of the BSS or if it is positioned 2) at the BSC site of the BSS. In case 1), the BSC should be considered as transparent for 16 kbit/s channels.

In case of 4,8 and 9,6 kbit/s channel coding when data is adapted to the 320 bit frames, a conversion function is required in addition to the conversion/rate adaption specified in GSM 08.20. This function constitutes the RAA. In case of 14,5 kbit/s channel coding, no RAA rate adaption is required because V.110 framing is not used.

The TRAU is considered a part of the BSC, and the signalling between the BSC and the TRAU (e.g. detection of call release, handover and transfer of O&M information) may be performed by using BSC internal signals. The signalling between the CCU and the TRAU, using TRAU frames as specified in the present document, is mandatory when the Abis interface is applied.

NOTE 1: If standard 64 kbit/s switching is used in the BSC, multiplexing according to ITU-T Recommendation I.460 should apply at both sides of the switch.

In figure 2.1, a possible configuration of the TRAU and the CCU is shown.

The functions inside the TRAU are:

– "Remote Transcoder and Rate Adaptor Control Function" (RTRACF);

– "Remote Speech Handler Function" (RSHF);

– The RAA function in case of 4.8 and 9.6 kbit/s channel coding;

– The RAA’ function in case of 14.5 kbit/s channel coding;

– The RA2 function;

– The transcoder function.

– Optionally the TFO functions (see GSM 08.62).

The functions inside the CCU are:

– "Transcoder and Rate Adaptor Control Function" (TRACF);

– "Speech Handler Function" (SHF);

– The RAA function in case of 4.8 and 9.6 kbit/s channel coding;

– The RA1/RA1′ function in case of 4.8 and 9.6 kbit/s channel coding;

– The RA1’/RAA’ function in case of 14.5 kbit/s channel coding;

– The channel codec function;

  • If AMR is supported, the Link Adaptation (see GSM 05.09).

The present document will not describe the procedures inside the TRAU and the CCU. The layout in figure 2.1 is only intended as a reference model.

NOTE 1: This recommendation assumes the DTX handler function to be a part of the Transcoder Function.

NOTE 2: This figure applies only for 4,8 kbit/s and 9,6 kbit/s channel coding.

Figure 2.1: Functional entities for handling of remote control of remote transcoders
and rate adaptors

NOTE 2: This figure applies only for 4,8 and 9,6 kbit/s channel coding.