Hi Expert,

I have a scenario here can anyone help me to undrstand is the behaviour is
correct on both cases?

• User A calls User B
• Negoziation for EVS codec
• User A put in hold User B
• REINVITE from User A, contains sendonly, with only EVS (codec negotiated
and used).
• REINVITE arrives to User B, it contains sendonly with all the codecs
handled by volte network in the following order: EVS, AMR WB, AMR NB.
• User B answer with 200 OK just with EVS and the call has not any call
quality issue.

• User B put in Hold User A
• User B sends REINVITE with sendonly containing only EVS,
• REINVITE arrives to User A with sendonly and it contains all the VoLTE
codecsin the following order: AMR WB, EVS, AMR NB.
• User A answer with 200 OK recvonly that contains only AMR-WB because is
the first in the list and the call quality has degraded

So is the codec negotiation in both cases OK I am asking since in one case
call quality is OK and in other case call quality is NOK?

Any RFC standard or reference  to understand completely the codec order and
priority to handle?
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