[OpenSIPS-Users] Add Contact header to ACK

[Julian Yap]

Hi,

I have an issue where a T38 fax UA which is calling outbound does not
add a contact header to an ACK when replying to the receiving party
before starting the initial RTP conversation.

As a result, the Re-INVITE from the receiving UA is misdirected and
never gets sent to the calling UA.

I'm wondering how I can add the Contact header to the ACK so that the
Re-INVITE then sends to the right place.  I tried writing the initial
Contact header to an AVP variable but the AVP does not persist by the
time I get to the ACK.

Below are the relevant SIP packets (changed details for privacy).

=== INITIAL INVITE from calling UA has a Contact header ===

INVITE sip:5551234 at mysipserver SIP/2.0
Via: SIP/2.0/UDP 8.8.8.10:5891;branch=z9hG4bK17BE
From: IPFax <sip:1006 at mysipserver>;tag=IPF_PORT_0001_17BD
To: <sip:5551234 at mysipserver>
Call-ID: 9fb5d1a5-fbf7-43ee-8eed-d96a2853d91c at 10.10.0.178
CSeq: 1 INVITE
Max-Forwards: 70
Contact: <sip:1006 at 8.8.8.10:5891>
User-Agent: Net Fax/IP_FAX-9.0.6039.885
Allow: INVITE, ACK, BYE, CANCEL, REFER, NOTIFY
Content-Type: application/sdp
Content-Length: 168

v=0
o=IPFax 0 0 IN IP4 8.8.8.10
s=SIP Fax Call
i=IPFax
c=IN IP4 8.8.8.10
t=0 0
m=audio 10946 RTP/AVP 0
a=rtpmap:0 PCMU/8000
a=ptime:20
a=sendrecv

=== ACK from calling UA does NOT have a Contact header ===

ACK sip:8085551000 at 8.8.8.20:5060 SIP/2.0
Via: SIP/2.0/UDP 8.8.8.10:5891;branch=z9hG4bK17C0
Route: <sip:64.111.178.50;lr=on;ftag=IPF_PORT_0001_17BD>
From: IPFax <sip:1006 at mysipserver>;tag=IPF_PORT_0001_17BD
To: <sip:5551234 at mysipserver>;tag=IPF_PORT_0024_DE2C
Call-ID: 9fb5d1a5-fbf7-43ee-8eed-d96a2853d91c at 10.10.0.178
CSeq: 2 ACK
Max-Forwards: 70
User-Agent: Net Fax/IP_FAX-9.0.6039.885
Proxy-Authorization: Digest
username="1006",realm="mysipserver",nonce="4f17fa650000012ed6c5fca98a3b6522fa041bfb558d4833",opaque="",uri="sip:5551234 at mysipserver",response="b9910d8e4b5994109ec671728365b2f6"
Content-Length: 0


=== REINVITE from receiving UA is misdirected ===

INVITE sip:1006 at mysipserver SIP/2.0
Via: SIP/2.0/UDP 8.8.8.20:5060;branch=z9hG4bKDE2D
Route: <sip:64.111.178.50;lr=on;ftag=IPF_PORT_0001_17BD>
From: <sip:5551234 at mysipserver>;tag=IPF_PORT_0024_DE2C
To: IPFax <sip:1006 at mysipserver>;tag=IPF_PORT_0001_17BD
Call-ID: 9fb5d1a5-fbf7-43ee-8eed-d96a2853d91c at 10.10.0.178
CSeq: 3 INVITE
Max-Forwards: 70
Contact: <sip:8085551000 at 8.8.8.20:5060>
User-Agent: Net Fax/IP_FAX-8.6.5262.504
Supported: timer,replaces,billing,presence,*
Allow: INVITE, ACK, BYE, CANCEL, REFER, NOTIFY
Content-Type: application/sdp
Content-Length: 359

v=0
o=IPFax 0 1 IN IP4 8.8.8.20
s=SIP Fax Call
i=IPFax
c=IN IP4 8.8.8.20
t=0 0
m=image 49198 udptl t38
a=T38FaxVersion:0
a=T38MaxBitRate:14400
a=T38FaxRateManagement:transferredTCF
a=T38FaxMaxBuffer:200
a=T38FaxMaxDatagram:72
a=T38FaxFillBitRemoval:0
a=T38FaxTranscodingMMR:0
a=T38FaxTranscodingJBIG:0
a=T38FaxUdpEC:t38UDPRedundancy