Cisco 7961G SIP is buggy

This week I updated the FreeSWITCH test box and decided to hook up a Cisco 7961G phone. To my surprise the 7961G would not register to the FreeSWITCH box. Further investigation showed that the 7961G with firmware 8.3.5 sends the following register to the FreeSWITCH box:

Via: SIP/2.0/UDP;branch=z9hG4bK8b5670ec
From: <sip:1000@>;tag=0016467650c80002ed42b648-ff2b3abc
To: <sip:1000@>
Call-ID: 00164676-50c80002-86027558-17f7cc0c@
Max-Forwards: 70
Date: Tue, 15 Apr 2008 21:21:55 GMT
User-Agent: Cisco-CP7961G/8.3.0
Contact: <sip:1000@;transport=udp>;+sip.instance<urn:uuid:00000000-0000-0000-0000-0016467650c8>”;+u.sip!”30018″
Supported: (null),X-cisco-xsi-6.0.2
Content-Length: 0
Expires: 3600

What’s totally wrong with this register is the following line:

Supported: (null),X-cisco-xsi-6.0.2

The “(” and “)” are not allowed there and break the register method. So Cisco’s 8.3.5 SIP firmware is non-RFC compliant.

A correct Supported line looks something like this:

Supported: 100rel, timer, precondition, path

The 7961G register is not even close. I could not believe that Cisco would release firmware with such a bad bug in it so I started to search for anything wrong in the 7961G config files. I couldn’t find anything. Then I decided to downgrade the 7961G to firmware release 8.3.3. Same problem. Finally I decided to downgrade the 7961G even further to firmware releaseĀ  8.2.1. And guess what. The 7961G sends a correct register request and subsequently registers fine with the FreeSWITCH box.

So what’s going on here? How could Cisco’s quality control miss this one? Or couldn’t they care less about SIP because they use SCCP with their Callmanager product? I don’t know but it sure seems like a good idea to steer clear from Cisco phones when using them with a non-Cisco VoIP PBX. Seems the general opinion in the Open Source VoIP community that you better buy Polycom, Aastra or Snom holds in this case.