AMR Codec Synchronization and Noise Distortion in VoLTE to 2G Call Scenarios

RAN
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1

Hi Experts.

In a call scenario from VoLTE to 2G how the AMR codecs are synchronized at runtime?

And if during the call VoLTE is using NB12.2 UL/DL codec and 2G is using 7.4UL/DL, then will there be noise distortion?

Thanks

2

During negotiation it gets appropriate codec up to 12.2 in GSM or EFR/HR.

3

Thanks!

Once the codec is negotiated in SIP message and call is established, then if 2G moves to a poor coverage, and its codec changes based on C/I, how will VoLTE user know which codec to tune to?

And if there is any mismatch in codecs will the user face distortion?

4

When Callee is on CSS network, MSC / Transcoder is involved, which adjusts codecs at Callee.

Caller (SIP based) codec remains as per its preference and compatibility with MSC / Transcoder codec sets.

So, callee codecs remain independent of caller codecs.

5

It’s just an observation that MOC UL Codec should be same as MTC DL Codec and if there is any mismatch voice muting is observed.

6

This is not normal, should be verified with e2e traces. At each moc and mtc end, transcoding at SBC/p-cscf(ims) or MSC/TRAU(cs) is done. Supported codec list at these nodes should be extensive and trancoding features should be defined as per vendor recommendations.
You can have both ues; one with evs and other with amr…one with amr wb and other with amr nb.