I am trying to debug a SIP issue, between an Asterisk 1.2.32 system that is behind a network device to which I don’t have ready access, which is performing NAT with possibly some kind of SIP ALG, and an Asterisk 11
system on a public IP.
My question is very specific, and I don’t need right now to discuss the ins and outs of the above setup.
What I am seeing is that when I have set up a call from the Asterisk 11
system, the 1.2.32 system is sending 200 OK, and sip debug shows the ACK response coming back from the Asterisk 11 box. However, the ACK
appears not to be understood, because the 200 OK gets re-sent, multiple times, and eventually gives up.
My specific question is, what values in the ACK does chan_sip (1.2.32)
use to match the ACK with the pending 200 OK? My understanding of the chan_sip.c code is not good enough to work it out for certain.
Here is the 200 OK (I’ve changed the address of the public endpoint):
Mar 30 10:20:20 VERBOSE logger.c: Retransmitting #5 (no NAT) to 188.8.131.52:5060:
SIP/2.0 200 OK
Via: SIP/2.0/UDP 184.108.40.206:5060;branch=z9hG4bK6bee4b53;received.111.11.111
From: “Tony Mountifield” <2011>;tag=as4ab948f7
CSeq: 102 INVITE
User-Agent: Asterisk PBX
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
Content-Type: application/sdp Content-Length: 21812345>12345>2011>
o=root 5732 5732 IN IP4 172.16.141.143
s=session c=IN IP4 172.16.141.143
m=audio 16282 RTP/AVP 0 101
a=silenceSupp:off – – – –
And here is the ACK in reply that is not getting understood:
<-- SIP read from 220.127.116.11:5060:
ACK sip:firstname.lastname@example.org SIP/2.0
Via: SIP/2.0/UDP 18.104.22.168:5060;branch=z9hG4bK36651b68
From: "Tony Mountifield" <2011>;tag=as4ab948f7
CSeq: 102 ACK
User-Agent: Asterisk PBX 11.5.0
So what is it about the ACK that is wrong?
Thanks for any help!