(Lync) Collocated or Stand-alone Mediation Servers?

In OCS 2007 R2 the Mediation Server was a separate role that needed to be installed whenever we wanted to leverage Enterprise voice or Dial-in conferencing usuage. In some instances depending on how many branch offices you had or how many concurrent calls you planned for your user base, this would increase the quantity of Mediation Servers in your enviroment. 

This was just one of the areas customers began to ask, “Why so many OCS servers?”

The Mediation Server by default in coupled with the Front End Server (Enterprise or Standard Edition) in Lync Server 2010. This alone saves you from having to deploy another physical box (and yes I said physical) because the Mediation Server does transcode audio from the Lync enviroment to the SIP Gateway or PBX and with transcoding different codecs such as G.711 to RTA (Real Time Audio) its best to have a physical box instead of a virtual one.

Now the question may come up as to what if I have a specific need to separate my Mediation Server in Lync?  Yes you can do this which leads to the title of the blog, “Collocated or Stand-alone Mediation Servers?”

They key things that i would like for you to consider when making this design decision is when planning ensure that after you take into account the processing requirements for non-media bypass PSTN calls and for the A\V Conferencing Server (collocated on the Front End Server) that there is enough processing power to handle signaling for the number of busy hour calls that need to be supported. Allow at least 30% of CPu for these interactions with the Front End Server.

Now if there is not enough CPU, then you must decouple the Mediation Server from the Front-End pool and create a stand-alone pool of Mediation Servers. In addition if you deploy PSTN gatewways that do not support the configuration of a pool of Mediation Servers then you will need to deploy a stand-alone pool consisting of a single Mediation Server.  Now keep in mind similar to the Front End Servers, Director Servers, and Edge Servers that you can DNS load balance Mediation Servers in a pool.   

Note: The number of PSTN calls that can be handled and the number of machines required in the pool will depend on the following:
The number of gateway peers that the Mediation Server pool controls
The busy hour traffic through those gateways
The percentage of calls that are calls that bypass the Mediation Server


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