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CUCM Phones rebooting themselves

Hi Everyone!

I have a customer that has been plagued with an annoying problem for a couple months now. We have had a TAC case open with Cisco and haven't been able to get anywhere with them. Here is the issue.

Periodically (at least once a day), a small group of phones registered to CUCM 7.0.2 reboot themselves with no administrator involvment. Now at first I thought it was a network problem (missing keepalives), but further investigation into the QoS configuration showed that there were no packet drops in the priority or call control queues and that MOS scores throughout the network were averaging 4.43 with a low score of 4.3. Second I considered the possibility of a firmware bug (8-5-2s) however the issue happens to different phones everyday and not necessarily the SAME phones. The issue moves around the network affecting different phones one day and other phones another day. The only thing that we have been able to identify is that the syslogs show transient connection errors and it seems to be around 9:00AM and 9:00PM when the phones lose connection.  Any ideas that anyone might have are GREATLY appreciated. Thanks for taking the time to read and consider.

Happy Holidays!!


Accepted Solutions

I came across this when looking for another problem.  Did you resolve the issue?

We had a similar issue when the DHCP lease time was set to anything other than infinite.

View solution in original post

Brandon Buffin

Are the phones using PoE. Have you ruled out a power problem? What does "show power inline" tell you? What happens if you power one of the affected phones with a power brick?


Brandon - I didn't even think about that as a possible cause. I will look into it and post my findings. Thanks for the input!

P.S - should I be looking for anything particular in the command output of the switch? I'm not real familiar with the PoE configuration in the switch...just know that they will only provide as much power as the device needs.

Hi There,

You should disable Power Inline on any port that doesn't require it.  You can do this by applying the power inline never at the interface level.

You can also use Show power inline to find out which ports are using POE and which wattage. 

You will also want to ensure that you have the correct power going to each phone model

Q. What are the power requirements for the various models of the IP phone models?

  • CP-7902G (6.3W)

  • CP-7905G (6.3W)

  • CP-7910-SW (6.3W)

  • CP-7910G (6.3W)

  • CP-7912G (6.3W)

  • CP-7940G (6.3W)

  • CP-7960G (6.3W)

  • CP-7906G (5W) (Class 2)

  • CP-7911G (5W) (Class 2)

  • CP-7941G (6.3W) (Class 2)

  • CP-7941G-GE (12.9W) (Class 3)

  • CP-7961G (6.3W) (Class 2)

  • CP-7961G-GE (12.9W) (Class 3)

  • CP-7970G (10.25W) (Class 3)

  • CP-7971-G-GE (15.4W) (Class 3)

  • CP-7985G (12.55W) (Class 0, Not full brightness)

  • IEEE 802.3af Device - Class 0 (15.4W)

  • IEEE 802.3af Device - Class 1 (4W)

  • IEEE 802.3af Device - Class 2 (7W)

  • IEEE 802.3af Device - Class 3 (15.4W)

Also if you need to change the POE Wattage used by the phone you can do this below:

A powered device might use more power than set by the power inline consumption command, so you must carefully make adjustments to the power budget. An accurate power budget protects the switch from an overcurrent condition.

In this example, the power budget is manually adjusted to 4 W on a specific port. When a Class 3 phone was connected, it required more power than 4 W:

Switch(config-if)# power inline consumption 4000

HTH, Please rate if so



Justin -

Thank you for your input. I carefully looked at the configuration of the PoE switches and found that the IP phones were always drawing the correct amount of power according to Cisco documentation. I took your recommendation and used the "power inline never" interace command to shut off PoE on non IP phone ports.

SOS-3560-SW# show power inline

Available: 370.0(w)  Used: 154.5(w)  Remaining: 215.5(w)

Is there anything else that anyone can think of that might cause this issue? Is anyone aware of a bug in firmware 8-5-2s? Should I downgrade or upgrade?


I came across this when looking for another problem.  Did you resolve the issue?

We had a similar issue when the DHCP lease time was set to anything other than infinite.

I'm currently experiencing the same issue running off of CUCM Business Edition version 7.1(5).  We've checked the network, CUCM configurations, power, etc. I notice that about 6 random phones reboot once or twice sporadically within the span of about 2 hours. This happens once every couple of days. We are currently running packet captures and have a TAC case open.

Did you happen to find the cause of this issue?? Thanks!

Could anyone be having solution to above problem pleeeeeeeease

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