HP Survivable Branch Communication zl Module powered by Microsoft Lync Planning and Design Guide 2011-02

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Design Considerations
Planning Call Capacity
Media Bypass Overview
In the traditional Lync architecture, Lync clients communicate with Mediation
Gateways, which then translate the calls for transmission to the PSTN (Media)
gateway. With Media Bypass, the Mediation Server still helps to establish the
PSTN call. However, after the call is established, clients can send Real-Time
Protocol (RTP) media traffic directly to the PSTN gateway, encoding their
calls with the correct codec themselves. Similarly, the PSTN gateway can send
the media traffic from the PSTN directly to the Lync client.
As illustrated in the figure, the SBM provides both the Mediation Server and
the Media Gateway, so the packet flow is the same. However, Media Bypass
still vastly enhances the solution’s scalability and audio quality because it
removes the need to translate the call at the Mediation Server, decreasing the
burden on the SBM and reducing latency.
Figure 2-2. Media Bypass