SIP Options


For some time now I have seen my Wireshark traces and the event log on the Mediation Server report an issue with regard to SIP Options. I finally was forced to pay attention to this item during a recent deployment.


In the image above the Source IP 10.2.85.31 is the Lync FE and 10.2.85.20 & 10.2.85.21 are both gateways. Lync here sends the SIP Options Request and both gateways reply with OK.

What do SIP Options do?
They are used by Lync to determine if the gateway\SBC is good and ready to accept calls from Lync (no that’s not a typo, this is in relation to outbound calls).

Lync sends a SIP Options request to the Gateway and expects an answer (apparently any answer will do) usually a 200 OK. These messages are sent every 4 seconds. If no response is received for a period of up to 30 seconds the route using this particular gateway is marked as down. 

If its the only gateway Lync will continue to attempt to route calls across it. If there is an alternate gateway available then this will receive the outbound calls instead.

Sometimes you may come across a gateway that sends SIP Option messages to Lync, in this case Lync will stop sending Options messages and instead reply to the options messages it receives with an OK. Lync will also send a SIP Option messages every 20 seconds to be sure all is good.

If Lync stops seeing the SIP messages from the gateway it will revert to taking over the role of sending messages in 5 minutes from the last Options message received.


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About Paul B

My name is Paul Bloem and I am employed at Lexel Systems in New Zealand as a Principal Consultant for Unified Communications. I have been working on enterprise voice solutions for over 20 years. My first 10 years were spent working for a Telco in South Africa (Telcom SA). This is where all the groundwork happened as I was exposed to just about every aspect of telecommunication you could imagine. I develop an interest in PBX technologies and eventually became the go-to guy. Next, I had a 10 year run at Siemens South Africa, most of my time there was as a Technical Trainer. During this time VoIP hit the world stage, I had the privilege of introducing VoIP both as H.323 and later SIP across the Siemens HiPath 4000 solution stack. In 2008 I immigrated to New Zealand with my newly attained MCSE, I was ready to go where no PBX Techie had gone before. I was employed to explore OCS 2007 and that was pretty much the beginning of the end for me. I have been working on OCS and Lync ever since. My current role focuses exclusively on Lync and associated technologies.. That includes pre-sales, consulting, architecture and design, training and support. I even get to play in the development space from time to time - focus on play ;-) I was nominated as a Microsoft VTSP for Lync early in 2013 and also awarded Microsoft's MVP award for Lync in 2014.
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