06-11-2020 09:21 AM
Hi,
We may have to apply a SIP profile to fix up media addresses in SDP, replacing internal address with the NAT external. In drafting the profile I've come across a few things I'm not clear on, could anyone comment on these?
(1) What's the significance of there being more than one "c=IN" field in the SDP? For example it seems that the CUBE's outgoing Invites always have two, one before and one after the "m=audio" field, same IP address in each.
v=0 o=CiscoSystemsSIP-GW-UserAgent 590 872 IN IP4 x.x.x.x s=SIP Call c=IN IP4 x.x.x.x t=0 0 m=audio 25636 RTP/AVP 8 18 101 c=IN IP4 x.x.x.x a=rtpmap:8 PCMA/8000 a=rtpmap:18 G729/8000 a=fmtp:18 annexb=no a=rtpmap:101 telephone-event/8000 a=fmtp:101 0-16 a=ptime:20
A SIP profile modifying "Audio-Connection-Info" re-writes the second instance but not the first.
It's tempting to think that the second "c=" is the effective one for audio, coming after the "m=audio" field. But that's not supported by the fact that some messages have only one "c=", and it appears before the "m=audio".
(2) Leading on from that, is there a reference document somewhere giving the field definitions recognised with SIP profiles?
Thanks, Tony S
06-12-2020 04:14 AM
06-12-2020 06:55 AM
So referring to that document it looks like I can modify the first entry with "Connection-Info"
request ANY sdp-header Connection-Info modify "x.x.x.x" "y.y.y.y" request ANY sdp-header Audio-Connection-Info modify "x.x.x.x" "y.y.y.y"
I need both because the messages that only have one entry have it before the "m=audio" and presumably that takes effect for audio.
Leading me to the other question, have you seen any document giving a reference list of field and header names used in SIP profiles? I have only been able to find examples, not reference material. So for example if I wanted to modify the "o=" SDP field I can't look that up in any document but would have to find an example.
Thanks, Tony S
06-12-2020 07:10 AM
06-12-2020 07:51 AM
My point, which I'm probably not making clearly enough is that I can't find a reference to say what Cisco's special name is for each of these fields. For example there's nothing that I can see in the RFC that would positively say that for the "o=" field we need to use "Session-Owner", and not for example "Originator"
o=<username> <session id> <version> <network type> <address type> <address>
The "o=" field gives the originator of the session (their username and the address
of the user's host) plus a session id and session version number.
06-12-2020 09:05 AM
Discover and save your favorite ideas. Come back to expert answers, step-by-step guides, recent topics, and more.
New here? Get started with these tips. How to use Community New member guide