Monday, 14 September 2015

IMS, VOLTE, Oneway Speech, UGC, CODEC

Problem Description
We were using RCS client for testing the Voice over LTE in operator Z, User was registered successfully, incoming and outgoing call connectivity was also ok. When call was made from RCS client to CS the call was ok and both parties could listen each other but when call was made from CS network to IMS network the RCS client could not listen the voice from CS network, even call was established successfully. 
IMS--(sip)--- UGC ---(bicc)-- CS Network.

No Alarm
Handling Process
We checked each and every point and could not find any issue, we changed voice codecs on UGC, on IMS side and even on CS side but no use.
Later we found that RCS client does not support clock rate more than 8000. When call is established from RCS client to CS network the clock rate 8000 is selected by RCS and hence it can lsiten the both way.
But when terminating call is established, CS network selects clock rate 16000 and same 16000 clock rate is selected from UGC towards IMS on SIP Trunk as well, so RCS client could not listen the voice.
we were using AMR-2(Clockrate 16000) with CS network on BICC interface so we could not change to GSM EFR to reduce the clock rate to 8000. As Operator Z was using AMR-2 in their network. 

Solution was decided that we have to change the clock rate on UGC and make it 8000 towards IMS side and 16000 towards CS side.
So it was decided that UGC will perform transcoding function, we will use AMR-2 on BICC interface with CS network and GSM EFR on SIP interface between IMS---UGC. We tried directly to change the clock rate on SIP interface but the ADD CODECCFG does not work on SIP trunks but only works for BICC,ISUP interfaces. So finally we decided to reduce the clock rate to 8000 for AMR and AMR-2 completely on UGC and for BICC interafces we can increase the clock rate on BICC Trunks. 
MOD CODECCFG: CODECID=105, CLOCKRATE=PKT8000;     //changing the clock rate for Codec AMR
MOD CODECCFG: CODECID=106, CLOCKRATE=PKT8000;     //changing the clock rate for Codec AMR-2
//Adding Codec AMR-2 on BICC interface and changing the clock rate to 16000
//Adding Codec AMR on BICC interface and changing the clock rate to 16000
//Adding the GSMEFR codec on SIPTG on UGC
Suggestions and Summary
Huawei RCS Client updated version will support clock rate of 16000. 

Budi Prasetyo

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