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.