Hi,

While interop with third party vendor sip device, we have got the following 
message exchange (Only SDP message shown for sake of clarity)

Device 1  Device 2

INVITE (no SDP) -------------------------->

<---------------------------- 200 OK (SDP shown below)
v=0
o=11701 0 0 IN IP4 172.26.29.33
s=-
c=IN IP4 172.26.29.33
t=0 0
m=audio 50000 RTP/AVP 0 101
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-11,16
m=video 50002 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42801f; max-mbps=108000; max-fs=3600; max-br=5125

ACK (SDP shown below) ------------------------->
v=0
o=- 4865 4865 IN IP4 172.26.29.5
s=-
c=IN IP4 172.26.29.5
t=0 0
m=audio 30250 RTP/AVP 0 101
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-15
m=video 0 RTP/AVP 96

REINVITE (SDP shown below) ------------------------->
v=0
o=- 4865 4866 IN IP4 172.26.29.5
s=-
c=IN IP4 172.26.29.5
t=0 0
m=audio 30250 RTP/AVP 0 8 18 102 101
a=rtpmap:18 G729/8000
a=fmtp:18 annexb=no
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-15
a=sendonly
a=rtpmap:102 G7221/8000
m=audio 30250 RTP/SAVP 0 8 18 102 101
a=rtpmap:18 G729/8000
a=fmtp:18 annexb=no
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-15
a=sendonly
a=crypto:1 AES_CM_128_HMAC_SHA1_80 
inline:YmJhYjY4YWM1MzRlYzFkNTZmZTg2Mzc5OGFmNDM1
a=rtpmap:102 G7221/8000

According to the RFC 3264 standard, REINVITE SDP should be like below. As the 
negotiated streams were two in the initial offer answer. The new stream should 
be added below the existing streams. Please correct me If I am wrong.

v=0
o=- 4865 4866 IN IP4 172.26.29.5
s=-
c=IN IP4 172.26.29.5
t=0 0
m=audio 30250 RTP/AVP 0 8 18 102 101
a=rtpmap:18 G729/8000
a=fmtp:18 annexb=no
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-15
a=sendonly
a=rtpmap:102 G7221/8000
m=video 0 RTP/AVP 96
m=audio 30250 RTP/SAVP 0 8 18 102 101
a=rtpmap:18 G729/8000
a=fmtp:18 annexb=no
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-15
a=sendonly
a=crypto:1 AES_CM_128_HMAC_SHA1_80 
inline:YmJhYjY4YWM1MzRlYzFkNTZmZTg2Mzc5OGFmNDM1
a=rtpmap:102 G7221/8000

Thanks,
Gaurav



This is confidential Ittiam property.

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