Planning for Media Bypass
Topic Last Modified: 2010-11-05
Media bypass is useful when you want to minimize the number of Mediation Servers deployed. Typically, a Mediation Server pool will be deployed at a central site, and it will control gateways at branch sites. Enabling media bypass allows media for PSTN calls from clients at branch sites to flow directly through the gateways at those sites. Lync Server 2010 outbound call routes and Enterprise Voice policies must be properly configured so that PSTN calls from clients at a branch site are routed to the appropriate gateway.
Wi-Fi networks typically experience more packet loss than wired networks. Recovery from this packet loss is not typically something that can be accommodated by gateways. Thus, we recommend that you evaluate the quality of a Wi-Fi network before determining whether bypass should be enabled for a wireless subnet. There is a tradeoff in latency reduction versus recovery from packet loss to consider, as well. RTAudio, a codec which is available for calls that do not bypass the Mediation Server, is better suited for handling packet loss.
After your Enterprise Voice structure is in place, planning for media bypass is straightforward.
If you have a centralized topology without WAN links to branch sites, you can enable global media bypass, because fine-grained control is unnecessary.
If you have a distributed topology consisting of one or more network regions and their affiliated branch sites, determine the following:
Whether your Mediation Server peers are able to support the capabilities required for media bypass.
Which sites in each network region are well connected.
Which combination of media bypass and call admission control is appropriate for your network.
Bypass IDs are computed, either directly or indirectly, depending on configuration by the administrator. In addition to enabling media bypass globally, you must enable media bypass individually on each PSTN trunk. If bypass is enabled globally but is not enabled for a particular PSTN trunk, media bypass will not be invoked for any calls involving that PSTN trunk. In addition, when media bypass is set to Use Site and Region Information, you must associate all routable subnets with the sites in which they are located. If there are routable subnets within a site for which bypass is not wanted, these subnets should be grouped within a new site before you enable media bypass. Doing so will assure that the unroutable subnets are assigned a different bypass ID.