Hello,
I've noticed that firmware 11.2.1 (I haven't tested for older versions) violates SIP specifications in an embarrassing way when sending a re-SUBSCRIBE within an existing dialog. More specifically, the phone (a 8851 in this case) doesn't use the previously received URI from the Contact header. Instead, it re-uses the R-URI from the initial SUBSCRIBE.
Please find below the cadence of SIP messages demonstrating the problem:
SUBSCRIBE sip:402@my-sip-proxy.net SIP/2.0
Via: SIP/2.0/UDP 2.2.2.2:5064;branch=z9hG4bK-e33ba6a1
From: "johntest-405" <sip:johntest-405@my-sip-proxy.net>;tag=c7976ef9660b6c8c
To: <sip:402@my-sip-proxy.net>
Call-ID: 14d1519-a9d4fd4d@172.17.173.14
CSeq: 60735 SUBSCRIBE
Max-Forwards: 70
Proxy-Authorization: Digest username="johntest-405",realm="my-sip-proxy.net",nonce="W+21WFvttCwi3gqyVA9svGyun5Faqj6X",uri="sip:402@modcom-
c",algorithm=MD5,response="aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
Contact: "johntest-405" <sip:johntest-405@2.2.2.2:5064>
Accept: application/dialog-info+xml
Expires: 120
Event: dialog
User-Agent: Cisco-CP-8851-3PCC/11.2.1
Content-Length: 0
SIP/2.0 200 OK
From: <sip:johntest-405@my-sip-proxy.net>;tag=c7976ef9660b6c8c
To: <sip:402@my-sip-proxy.net>;tag=as74e10ebb
Call-ID: 14d1519-a9d4fd4d@172.17.173.14
CSeq: 60735 SUBSCRIBE
Server: modCOM v2 SIP Server
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY, INFO, PUBLISH, MESSAGE
Supported: replaces, timer
Expires: 120
Content-Length: 0
Via: SIP/2.0/UDP 2.2.2.2:5064;rport=5064;branch=z9hG4bK-e33ba6a1
Contact: <sip:atpsh-5bed8859-3719-2@3.3.3.3>
The URI from the response's Contact: header should be used for all subsequent
in-dialog requests from the phone. Instead:
SUBSCRIBE sip:402@my-sip-proxy.net SIP/2.0
Via: SIP/2.0/UDP 2.2.2.2:5064;branch=z9hG4bK-81b84571
From: "johntest-405" <sip:johntest-405@my-sip-proxy.net>;tag=c7976ef9660b6c8c
To: <sip:402@my-sip-proxy.net>;tag=as74e10ebb
Call-ID: 14d1519-a9d4fd4d@172.17.173.14
CSeq: 60736 SUBSCRIBE
Max-Forwards: 70
Proxy-Authorization: Digest username="johntest-405",realm="my-sip-proxy.net",nonce="W+21WFvttCwi3gqyVA9svGyun5Faqj6X",uri="sip:402@modcom-
c",algorithm=MD5,response="aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
Contact: "johntest-405" <sip:johntest-405@2.2.2.2:5064>
Accept: application/dialog-info+xml
Expires: 120
Event: dialog
User-Agent: Cisco-CP-8851-3PCC/11.2.1
Content-Length: 0
Public IPs, hostnames and challenge responses have been edited for privacy/seccurity reasons.
BR,
George
