Lync Dial Plan Redundancy

It gets a bit frustrating trying to match gateways to Lync for good functionality. It is even more frustrating when its not a certified gateway.

With this introduction I fire into a new post about gateways, resilience and fail-over options.

Usually when an alternative route exists for fail over one assumes that the trusty SIP options will take care of failing over in the event that a positive response isn’t received from the gateway.

But what if the SIP Options responses are positive and yet there is another issue? Possibly routing beyond the gateway in question…

SIP Options aside, there is another influencing factor that triggers fail over – SIP Error messages!

Lync will not fail over on 4xx SIP Response codes, an error code reporting a 5xx SIP Response is required for Lync to attempt an alternate route.

For example, if a gateway was responding positively to SIP Option requests from the Lync Mediation Server but was unable to route to the ITSP a 408 SIP Response code may be received (Request Timeout).

As this is a 4xx SIP message no fail over will be attempted!!!

All certified gateways usually send the correct response codes as described by Microsoft for fail over. But we are in a world where all things are not perfect and so…we may need to tell Lync to respond differently to a the 408 SIP Response code.

How to do this?
As with all things truly powerful…Lync Powershell of course.
You can set a SIP Response Code Translation Rule per Gateway and below is an example:

New-CsSipResponseCodeTranslationRule -Identity “PstnGateway:” -ReceivedResponseCode 406 -TranslatedResponseCode 503

The Identity MUST be in the format PstnGateway:/
You can check the naming convention in Lync Control Panel Voice Routing – Route – Associated Trunks.

TechNet reference:


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.
This entry was posted in Fail over, SIP Options, SIP Response Code Translation. Bookmark the permalink.

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