[c-nsp] SIP and NAT/PAT issues

[Church, Chuck]

Anyone,

	I'm looking for a good whitepaper on SIP call setup, and how the
RTP is setup after the SIP portion is done.  I looked around a bit, and
didn't see anything with as much detail as I'm looking for.  I've got a
2650 with a T1 internet connection, default route.  It's doing QoS,
prioritizing VoIP in both directions.  It's also doing NAT/PAT and CBAC
firewalling.  Yesterday I had an issue with one way voice on a couple
different SIP phones, and an ATA.  All three are different brands, and
access a SIP proxy held at a commercial VoIP provider out on the 'net.
>From what I could see from the 'sh ip inspect sess' was that CBAC got
really confused, and was trying to send an RTP stream inbound to the
wrong device.  The destination it was trying didn't exist, and the ARP
entry for it was incomplete.  Rebooting the router made the problem go
away.  Anyone got any tips on combining PAT/SIP/CBAC?  I did see some
bugs relating to 12.3.18 and one-way voice.  I threw 12.4.8 on last
night, hoping it helps.  The problem has happened only twice in the last
8 weeks, and rebooting the router fixed it both times, so I'm leaning
more towards a software bug versus a config issue, but any tips would be
greatly appreciated.  

Thanks in advance,
 
Chuck Church