Media Bypass Gotcha

After reading several blogs, tech-net articles and working with premier support, it was discovered that you MUST have the subnet of your SBC defined in Lync.  Without this, the SBC can not be given a bypass ID and thus your lync clients / phones will never send media traffic to the SBC.

In this example the IP of the SBC is

To figure out if you’re running into this problem you will need to log onto your Mediation Server, launch ocslogger and turn on full tracing of the mediation server

With logging turned on make a PSTN call.  Once the call goes through, hang up then examine the OCSLogger file.  Click analyze.  In the find field type “findbestmatch”

You’ll notice that it states “No Subnet found for”.  Now if you recall, for a Media Bypass call to work, the Bypass ID of the client MUST match the Bypass ID of the gateway (note this is with Media Bypass set to “Use Sites and Region Configuration”.  CAC is NOT enabled in this environment) …so lets search for the bypassID of the gateway.  In the same screen type “bypassid”

You’ll see it’s searching for the bypass ID of gateway.  Go one line down

Bypass ID = Null, thus no bypassID is assigned to the gateway.

All that’s needed is to add the Subnet of the gateway to Subnet field in Lync Control Panel (network configuration > Subnet)

Once this is done, should you have the other portions of Media Bypass set up properly, Media Bypass will work.

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