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 1-6. Establishing the SIP Call
4. The RTP traffic flows for the duration of the call.
Calls between branch users remain within the LAN while calls between a
branch user and a user at a different site pass over the WAN connection. In
either case, for simple two-way calls the RTP traffic passes directly between
the clients, making the Lync solution quite scalable. See Figure 1-4 on
page 1-11 and Figure 1-5 on page 1-12.
5. When a user ends the call, the Lync client sends a SIP Bye message. The
other party sends an OK, and the call is terminated.
The process that you just examined is for a basic audio call. The SIP and RTP
traffic for a conference that involves a branch user must pass through a
Conferencing server at the central office as shown in Figure 1-7.