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

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SBM Overview
SBM Role in a Microsoft UC&C Solution
Figure 1-9. Establishing the Call
4. RTP communications continue to pass through the SBM’s PSTN gateway
and over the PSTN line. (Unless you are using Media Bypass, the RTP
traffic passes through the Mediation Server before the PSTN gateway.)
Often, you route local branch users’ PSTN calls out the SBM’s PSTN connec-
tion as described in the steps above. However, the SBM can also route calls
through PSTN gateways at other sites; the flow all depends on the routing rules
defined for the branch site. For example, you might use routing rules to route
calls that would be long distance from the branch to a PSTN gateway where
the call is local or cheaper. This is called least cost routing.