the value is in milliseconds, meaning the default setting is 10 seconds. This actually determines how long should a call wait for the gateway until it declares it “Offline”. This will generate errors (2 per failed call) on your Lync servers and is actually a Lync self-inflicted error. Failing to provide that (183 “Session in Progress” can be pushed here but that won’t benefit you if you’re still waiting for that ring…) will cause the mediation server to decide that the call didn’t respond and to mark the gateway as unavailable. The Lync mediation server is expecting a “SIP 180 Ringing” within 10 seconds of initiating the call. Within 10 seconds after initiating the call, the mediation server will send a “Cancel” request to the gateway and will terminate the call: 19:25:49.640 INVITE SIP/2.0ġ9:25:49.729 SIP/2.0 100 Tryingġ9:25:49.730 ( lgr_psbrdif)( 656225) pstn send -> PlaceCall 19:25:50.087 ( lgr_psbrdex)( 656229) pstn recv PSTNDisconnectCallĬlearly, the gateway is available and responding, but the mediation server is somewhat impatient.ĭoing a bit of digging around, it appears there’s a setting for this. Looking further at the logs, I see the following strange behaviour:Īs I’m still waiting for the PSTN to connect the call (this would normally be a “PSTN Call Alerting” message), I see that the mediation server decided to abandon ship! So for the time being I’m not really buying what the Lync mediation server is selling. The next phase would be the gateway immediately sending a “PSTN Place call” to the PSTN, hopefully receiving a “Proceeding” instantly from the PSTN, meaning so far we’re fully communicating. This, for me, will close the deal on the “Gateway no responding” – this is a great response if you ask me. The mediation server sends a SIP Invite that will normally be answered immediately by the gateway with a “100 Trying”. I went to the gateway (AudioCodes M1000B) for answers and the logs were showing something very weird Looking further at the Lync Monitoring Reports, I noticed the following:ġ2000 reason=”Routes available for this request but no available gateway at this point” It seemed funny, because all other calls were successful, I have not exhausted the available PRI channels I had, the gateway didn’t seem to lose connectivity for a split second and SIP options are accepted and replied to on both ends. The cause, according to the mediation server, was that “ All gateways available for this call are marked as down“, and the resolution, surprisingly, was to “ Verify that these gateways are up and can respond to calls.” I had a very annoying issue lately when an installation of a new gateway resolved in some calls (specifically to US numbers) dropped by the Skype for Business mediation server saying “ A call to a PSTN number failed due to non availability of gateways.”
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