SIP 503 for Third party SIP client in CUCM

[kanchuen01]

We have upgraded our CUCM from 8.6 to 11.5 recently, our user reported that their third party SIP client has a call drop issue. They tried to use the self-developed SIP client to make an outgoing calls and they found that the call drop on every 4 trials and they checked from the log that it is showing 503 service unavailable. I try to download another third party SIP client and no problem occurred. Does anyone have any idea on what happened for this issue? Thanks

[W S H FERNANDO]

Hi kanchuen01,

can drop mean, during an Active call or before establishment ?

Regds
Sasith

[jaredkelsey]

I have the same problem.
A Third party SIP device in CUCM, device sends an Invite to CUCM, gets a 100 Trying, then a 503 Service Unavailable with this message: "399 xxxxxxxxx "Unable to find a device handler for the request received on port 5060 from x.x.x.x"
I replaced my server name and IP with x's