[cisco-voip] Codec negotiation

[Wes Sisk]

SCCP devices advertise capabilities on registration.  Those capabilities are never renegotiated unless video is added/removed/invoked.

A little insight here - 
CM tells the phones the codec it *should* receive in the OpenReceiveChannel sent to the phone. However, the phones do not trust that.  The phone figures out the codec it is receiving based on the first few RTP packets received.

If you are seeing ?? under codec I would be more suspecting of RTP not arriving at the phone.


SIP and H.323 advertise codecs on a per-call basis.  MGCP advertises codecs once during registration.

Regards,
Wes

On Dec 7, 2011, at 2:30 PM, Scott Voll wrote:

can anyone tell me how Codec negotiation works?  Specifically what ports it works on?

I have telecommuters using IPC 7.0.5 connecting with anyconnect (2.5) connecting to an ASA at the head end.  Calls to inside 7961's work fine.

but I also have 881's doing site to site VPN with 7961 hanging off the back coming into the same ASA.  That phone can call internal 7961 also.

The problem comes from IPC telecommuters calling 7961's behind the 881's.  When you place the call, it rings, they answer, the timer increments up.  But with a ?? it does not show a Codec.  It looks like we never negotiate the Codec.

is this a Version problem?  CM is 7.1.5 and ASA is 8.4.2.  I THINK it worked with ASA version 8.2.4 (but I Can't downgrade to double check).

Any other ideas?

I have a TAC case with the ASA team and they are like ya, the vpn connections work.... open a new ticket with the voice team.  And before I did so, I figured you guys are really smart and probably have deal with these kinds of issues.


Scott
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