Thursday, 20 June 2013
SIP Option from Mediation Server to Peer Gateway
1.1 Step 1
Lync Mediation server sends out SIP OPTIONS requests continuously to try to communicate with its next hop.
1.2 Step 2
If no response is returned Lync Mediation Server raise event ID 25051
1.3 Step 3
If mediation Server doesn’t receive response for five consecutive SIP OPTIONS then it raise event ID 25061 and 25052 and consequently marks the gateway "down".
1.4 Step 4
Also Mediation server informs Lync FE server about GW being down and hence seek alternate route for calls.
1.5 Step 5
Mediation Server checks GW status by sending SIP OPTIONS every 1 minute and as soon as it get 200 OK response from GW. It will put the GW back in service.
However, I have experienced that it takes ~10-15 mins for Front End server to route the calls back to allegedly “down” GW.