Cloud Connector Edition (CCE) 503 Proxy Invite Failed

Had a very strange one the other day. A customer reporting not be able to receive some calls via a CCE. I do love good a CCE fault.

As this was connected to an AudioCodes SBC, the first thing I did was open up Syslog Viewer and fire some calls in. Straight away I could see the calls were being rejected by mediation - “SIP/2.0 503 Proxy INVITE failed Error: Unable to establish a connection”.

First I checked all services were running on the edge and mediation (they were). They had an uptime of 2 days, so nothing should have gone stale.

Thinking about the error mentioning proxied invite and the flow of calls into 365, I thought that maybe the mediation is unable to reach the edge or the edge cannot reach 365. I checked event viewer and nothing.

On a whim, I checked the firewall on both, and the CS RTCSRV (Front-End service) on the edge was disabled. Enabled this and all working again! Weird…

Looking at the SBC logs can see that calls started failing at midnight that morning, no one logged in to the server according to the event viewer so will chalk it up to a bug somewhere. I’ve also enabled firewall logging in case it happens again.