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New Member

SIP inspection


We are trying to setup a SIP trunk between Avaya and Nortel through Cisco ASA. The SIP session seems to be successful and we can dial from Nortel to Avaya. The problem is that after dialing the phone rings but two ends can not hear each other. That is RTP (voice) communication is not working.

As part of SIP, both the PBX send the IP address and port number to connect to to establish voice session.

My assumption is that as we are NATing on ASA the TCP communication works but the original IP address and port numbers in SIP header doesn't change due to which routing breaks.

I tried using SIP inspection on ASA and that didn't work.

Any suggestions are appreciated!!

Thank you.


Re: SIP inspection


I would also think this is a routing issue.

Could you post the relevant part of your configuration?


New Member

Re: SIP inspection

We have several SIP trunks at work and SIP inspection is needed if you're NATting the IP of the endpoint(s).  SIP inspection re-writes the addresses in the packet.

With SIP inspection turned on try using "debug sip" while attempting a call.  Use with caution as, with all debuging, it can quickly overwhelm your screen but it ends when there is no more SIP traffic.  I found it very useful when we initially set our trunks up.

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