In the last two weeks I've encountered this exact problem twice and I am not sure what could cause it. I have a SIP 7975 phone registered and working just fine then out of the blue when someone tries to dial the extension on the phone nothing happens. The digits aren't displayed on the phone, just nothing. Doesn't matter if I dial on hook or off hook as soon as the dial string completed the window that should show the number dialing shows nothing. The first time it happend I tried resetting the phone which didn't work so I replaced the phone with the same config to get it working again. Today I had the problem again on a completely different user's phone, this time a reset from CUCM resolved the problem. CUCM is 8.5(1), firmware on the phones is SIP75.9-3-1SR2-1S.
I did some searching but wasn't able to find anything that matched this situation. Thanks for help in advance.
I would start with checking CallManager and verify that you don't have any database issues (see link below). I would also check the phone status message to see if anything is getting logged prior to the issue.
IntroductionCUCM Routing RulesDial String implementation PolicyCUCM Routing LogicSIP URI Call Routing Analysis+++ Case Study: 1 ++++++ Case Study: 2 +++Conclusion
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