Cisco 7941 Phones

By reuben, 16 April, 2006

A few weeks ago I bought a brand new cisco 7941 phone to replace and old ATA at home which we use to call Sydney a lot.  It's a whole lot cheaper than using Telecom, our NZ carrier, for these calls, and the setup has worked fairly well with the ATA.  However as I was able to get a real phone at a good price through work I decided I would do so before circumstances changed and I had to pay full retail.

Little did I know the amount of time and hassle involved in getting the phone to work.  You see, cisco don't support these phones in a non cisco CallManager environment - which is fair enough.  But they claim that the firmware is fully SIP compliant, which led me to believe it would be fairly straightforward to get to work with our IP telephony supplier in Sydney.

Indeed it is possible to get to work.  I know, because as of now I have it registering with Asterisk on my server which runs SIP.

But it was a pain to get this far, and I'm still not done.  Within 3 days of be getting the phone the phone had lost it's flash, but after a few days of hassles I managed to get my hands on an RMA'd unit from cisco which I was entitled to as the unit is under maintenance.  It looks like it may have had a complete failure of the flash chip as when I consoled to it and rebooted repeatedly, it jammed up "waiting for flash..." about 4 lines into the boot.

Cisco's previous model in this line was the 7940 series, which are great phones, but don't require the cnf.xml file config style, and are well documented on CCO.  They're easy to get to work - I bought one home from work one night and had it fully registering in about 10 minutes and could make calls immediately.  But as the 7941 is so new and the SIP image has only been out since early March, there was next to *no* documentation on config files.

I opened up a TAC case requesting the information but in the end the engineer came back and said it was unsupported and he couldn't find the information or tell me much more.  But he did assume me he'd pass my requests on for the information to be made more freely available, and did leave the distinct impression that it may be better documented in the future.

Anyway, I thought I'd post what information I could find up on

I've managed to get the phone working properly now, but I've run into a temporary problem caused by some slightly different behaviour that the phone exhibits compared to the way many other phone work.  My SIP provider are running an old and what appears to be buggy version of Asterisk that is not fully RFC compliant, and does not properly use the Via: header in the SIP header packets.  It erroneously uses the UDP source port to return the traffic, and because the 7941 does not use port 5060 for *both* source and destination as most phones do (the SIP RFCs allow this) the return SIP/UDP packets get lost, and the phone can't register or establish any sort of session.

However it all works if I register to my local Asterisk server, and then have that register to the upstream provider.

So for now we have a 90% good setup, but I really would like to get that Asterisk box out of the equation and go phone to gateway directly connectivity.........

Update:  As of mid 2006, I ended up spending much time on this and managed to do away with the Asterisk box altogether.  It required a setting be changed on the upstream SIP server to not try and do any clever NAT on my registration.  Additionally the phone registers to other SIP gateways without the workaround now too.

Update 2:  I have had a number of people requesting me send the SIP firmware files for this phone.
PLEASE DO NOT ASK ME FOR THESE FILES, I AM NOT LICENSED TO REDISTRIBUTE THEM.  If you do not have them, or require upgrades, contact the cisco reseller you bought the phone off and ask them, or better still, get a maintenance contract for the unit.