Hello,
Query No. 1

Suppose offer sent by the first machine is

 

m= audio 49230 RTP/AVP 0 8

 a=rtpmap : 0 PCMU/8000

 a=rtpmap : 8 PCMA/8000

 

i.e. - it supports g711Alaw and g711Mulaw for both Rx and Tx.

 

 The second machine supports g711Alaw for Rx only and g711Mulaw for Tx only.

 So suppose he sends a 488 error response with the following sdp details

 

  m= audio 5598 RTP/AVP 0

  a=rtpmap : 0 PCMU/8000

  a=sendonly

  m= audio 5598 RTP/AVP 8

  a=rtpmap : 8 PCMA/8000

  a=recvonly

 

How should the first machine respond to the 488 error message ?

 

An ACK would definitely go as a response to 488. And the first machine can issue a new INVITE, But will the new INVITE has to as offered as in option 1 or option 2 ?

 

Option 1

m= audio 49230 RTP/AVP 0

 a=rtpmap : 0 PCMU/8000

m= audio 49230 RTP/AVP 8

 a=rtpmap : 8 PCMA/8000

 

or send a new INVITE with

 

Option 2

 

m= audio 49230 RTP/AVP 0

 a=rtpmap : 0 PCMU/8000

 a=recvonly

m= audio 49230 RTP/AVP 8

 a=rtpmap : 8 PCMA/8000

 a=sendonly

 

Query No. 2 

  Suppose offer sent by the first machine is compliant with RFC 3264 and sends an offer as mentioned below :

 

m= audio 49230 RTP/AVP 0 8

 a=rtpmap : 0 PCMU/8000

 a=rtpmap : 8 PCMA/8000

 

i.e. - it supports g711Alaw and g711Mulaw for both Rx and Tx.

 

 The second machine supports g711Alaw for Rx only and g711Mulaw for Tx only.

 So if an answer is not compliant with RFC 3264, there are all possibilities that an answer be generated as mentioned below :

 

  m= audio 5598 RTP/AVP 0

  a=rtpmap : 0 PCMU/8000

  m= audio 5598 RTP/AVP 8

  a=rtpmap : 8 PCMA/8000

 

which is against the specification of RFC 3264 (offer has come with 1 m line , but answer being sent in 2 m lines)

 

Then what should the first machine(the one who initiated the offer) respond with ?

Send an ACK followed by BYE or ignore the 2 m lines and   try to establish the call

Using coder 0 (PCMU) ?

 

Thanks in advance,

Prabha N

 

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