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IP Phone Reboots often

Anand Narayana
Frequent Contributor
Frequent Contributor


I have a remote site on which the IP phones keeps rebooting very often, I believe keepalive packets are losing often. Is there any tool where I can check what exactely causing this issue? because my Softphone works fine, but only the hard phones 7940/76960 keeps rebooting in the recent days, I have 15 IP phones in the remote location. Any help would highly appreciated.


Jaime Valencia
Hall of Fame Cisco Employee Hall of Fame Cisco Employee
Hall of Fame Cisco Employee

CUCM trace with keepalive option checked or a sniffer trace are the only ways



if this helps, please rate



if this helps, please rate


How are they powered? That might be a symptom of an overloaded PoE switch.

I am in a similar position to the original poster of this question. Symptoms seem to only occur when a machine with a 10/100/1000 NIC is also in the loop.

How would you measure whether or not the PoE is overloaded? Do I really need to get the ampmeter out?

Reading around the 802.3af (2005) standard there seems to be a validation by the switch to see if power is needed. Apparently the circuit checks to see if the resistence on the circuit is between 15 and 33 kilo ohms. My current investigations are looking at whether or not the Gb NIC is adding resistence to the circuit.

I would interested to hear from anybody that may have had to measure this


Hi Aanand

All ip phones rebooting? What is the round trip .some time due to long round-trip delay /keep alive lost ,Check in CCM event logs for that phones

Which POE switch are you using? Check the logs of switch any issue in line power having issue.

If there is no logs related to inline power .Then check and upload the ip phone logs by browse the IP Phone ip .Also output of debug display option

*Hope this help*Pls rate it*


Thanks for the suggestion, but I also did a firmware upgrade but still the phones keeps rebooting. I am using 3Com switch & I have connected a separate power adaptor too for the phones. Below is the output of the debug in the one of the IP phone. Rebooting happens when I try calling some extension or receiving calls, transfer & so on. Rating for the your answer will be depend with the suggestion you provide.

2008-10-01 14:44:09.400 Code:dd04, P:0, S:12300900

Phone Task Call Stack:






System Regs: CPSR=2000003f

R0=d096eb14 R8=00000001

R1=000006cc R9=00400128

R2=00000000 R10=0000f0d0

R3=00000051 R11=736bdfdd

R4=0048585c R12=004ef13f

R5=2fab3a74 R13=0040dd48

R6=00485854 R14=000460df

R7=00000000 R15=000451e8

I still suggest that it is PoE related but do not know how to prove it.

In your situation activity on the phone could be putting additional load on the PoE circuit. The additional load then causes the amps, watts, volts, etc.. to drop below a tolerance threshold on the phone causing it to reboot. But this is all theory which I need help in proving/disproving.

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