Cisco Phone Unregisters from time to time

[JST]

I have a Cisco SIP phone in my home office and it is normally working just fine, but from time to time it decides to unregister and then I cannot make any calls. Oddly enough the phone allows me to start the call, but then 3CX is telling me that the phone isn't registered... I have already checked the registration expiration and it is set to 600 which is just 10 minutes. So, way below the 30 minutes limit.

The problem normally resolves itself within the next 30 minutes... Any ideas what could be wrong?

Thank you!

 

[YiannisH_3CX]

Hello @JST

Is this phone a local extension? Is it in the same network/subnet as the PBX? Also what firmware are you running on the Cisco phone?

 

[JST]

The phone is local, but it is on a different subnet. The firmware on the Cisco phone shows as 9.3.1 in 3CX.

My wife's Yealink desk phone and our Gigaset phone seem to work just fine.

Any ideas?

 

[DSXVOICE]

IS there a SonicWALL in the mix?

 

[JST]

No, I am using a Sophos SG firewall. Did you find that the Cisco needs additional ports? If you had to add anything to the SonicWALL, I might be able to add the same to the Sophos.

Thank you for your reply!

 

[YiannisH_3CX]

Assuming this is an SPA phone try downgrading the firmware to the 3CX supported which is 7.6.1 and see if that works.
https://www.3cx.com/Sip-Phones/Cisco-SPA/

 

[JST]

It's a Cisco 7975G. I can try to downgrade, but I don't see how this could change anything. Let me see if I can find the firmware listed in your post on the Cisco support page.

 

[YiannisH_3CX]

Since the phone is not in the supported list i cannot guarantee that the phone will work properly even if you do downgrade. give it a try though