Topic Last Modified: 2010-07-08
Media bypass refers to removing the Mediation Server from the media path whenever possible for calls whose signaling traverses the Mediation Server. This feature is new for Communications Server 2010.
The Mediation Server works in concert with the Communications Server 2010 endpoint involved in a particular call to the public switched telephone network (PSTN) to determine whether media from that endpoint can be sent directly to the IP-PSTN gateway, IP-PBX, or Session Border Controller (SBC) at an Internet Telephony Service Provider(ITSP) without needing to traverse the Mediation Server.
Bypassing the Mediation Server can result in improved quality by reducing latency, needless translation, possibility of packet loss, and the number of points of potential failure. Scalability can be improved because, for bypassed calls, media processing is eliminated from the Mediation Server. Freeing up the CPU in this way complements the Mediation Server’s ability in Communications Server 2010 to control multiple gateways, a capability that is new to this release. Where a Mediation Server and an IP-PSTN gateway or PBX media termination point are located at different sites connected by one or more WAN links with constrained bandwidth, media bypass lowers the bandwidth requirement by allowing media from a client at a branch site to flow directly to a gateway or media termination point at the branch site without having to flow over the WAN link to Mediation Server at the central site.
As a general rule, enable media bypass wherever possible for the advantages cited previously. In addition, enabling media bypass can reduce the number of Mediation Servers that your Enterprise Voice infrastructure requires.
Requirements for Media Bypass
When planning your Enterprise Voice infrastructure, it is important to decide the global mode for media bypass (either "Always Bypass" or "Use Site and Region Information", as well as whether bypass can be enabled for a particular trunk connection to a peer (IP-PSTN gateway, IP-PBX, or SBC at an ITSP) of the Mediation Server. Media bypass can be employed when the following conditions are met:
- Media bypass is enabled globally as well as for the trunk
connection to the peer. Bypass should only be enabled for the trunk
connection if the peer supports the necessary capabilities for
media bypass--the ability to handle multiple forked responses (also
known as early dialogs) being the most important. Before you deploy
media bypass, contact the manufacturer of your gateway or PBX, or
contact the ITSP to obtain the value for the maximum number of
early dialogs that the gateway, PBX, or SBC can accept.
- There is a routable path from the Communications Server 2010
endpoint to the gateway peer for media. If there is no such
routable path--for example, many SIP trunking providers only allow
their SBC to receive traffic from the Mediation Server--, then
media bypass must not be enabled for the trunk connection in
- The Communications Server 2010 endpoint and the peer are well
connected. During deployment, if you enable media bypass globally
and enable media bypass for one or more trunk connections by
running the New-CsNetworkMediaBypassConfiguration cmdlet
with the –AlwaysBypass parameter, good connectivity is
assumed and media bypass is always applied to calls that involve a
Communications Server 2010 endpoint and a peer. Otherwise, the
global configuration can be set to use site and region information.
When media bypass is set to use site and region information, you
must associate the subnets associated with Communications Server
2010 endpoints with particular sites. You must also associate the
subnets of the trunk connections to the IP-PSTN gateway, IP-PBX, or
SBC with particular sites. If the Communications Server 2010
endpoint and the peer involved in a call are deployed at the same
site, or at different sites that have no bandwidth constraints on
WAN links between those sites, media bypass will be employed.