[This is pre-release documentation and subject to change in future releases. This topic's current status is: Milestone-Ready]

Topic Last Modified: 2010-03-19

New for the Mediation Server in Communications Server 2010 is the ability for a single Mediation Server to control multiple (N) gateways. In previous releases, there was a 1:1 ratio of Mediation Server to Gateways. Also new for Communications Server 2010 is the ability for a Mediation Server to be deployed as a pool; this pool can be collocated with the Registrar on an Enterprise Front End pool, or can be a standalone pool. When collocated with the Registrar, the pool size can be at most 10 (limit of the Registrar pool size). Taken together, these new capabilities increase the reliability and deployment flexibility for Mediation Servers, but they require associated capabilities in the following peer entities:

A Mediation Server pool must have a uniform view of the peer gateway entity that it interacts with. This means that ALL members of the pool access the same definition of the peer gateway entity from configuration, and are equally likely to interact with it for outgoing calls. Thus, there is no capability to segment the pool such that some Mediation Servers only talk to certain gateway peers for outgoing calls. If such segmentation is necessary, a separate pool of Mediation Servers must be used. This would be the case, for example, if the associated capabilities in IP-PSTN gateways, SIP Trunks, or IP-PBXexs to interact with a pool as detailed above are not present.

A Communications Server 2010 deployment assumes that a particular IP-PSTN gateway, IP-PBX, or SIP Trunk peer depends on only a single Mediation Server pool; calls are routed to that pool by the Communications Server 2010 Front End/Registrar so that they can get to that gateway peer.

For SIP Trunks, IP-PBXes, and IP-PSTN gateways where a separate pool of Mediation Servers must be used (due to the fact that these entities do not support the correct capabilities to interact with a pool), the following scheme can be used to achieve redundancy:

The number of Gateways that a particular pool of Mediation Servers can control is dependent on the number of calls that are bypass. Bypass calls imply that the media does not flow through any Mediation Server in the pool. This in turn implies that a Mediation Server in the pool can handle many more calls, since only signaling plane processing is necessary. Contrast this to a case where the media flow can never bypass the Mediation Server.