Snom ONE IP, Техническое руководство

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Deploying the snom ONE IP Telephone System
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do not register cannot be called and SIP devices that do not successfully authenticate
cannot make outbound calls. A media server is a device that handles any kind of media
or RT, such as a voicemail server, a conference server, an IVR server, and a music on
hold server.
User Agent User Agent
Proxy Server
User Agent
Registrar Server
Figure B-1. Different Types of User Agent Servers (UASs)
Back-to-Back User Agent (B2BUA)
A B2BUA essentially bolts two user agents together in a back-to-back fashion, similar to
two people standing back to back. A B2BAU establishes a two-legged call, keeping the
SIP server in the middle of the call to orchestrate the details. One side of the session
acts as the SIP UA server that receives the calls; the other side acts as the SIP UA client
that establishes the other leg of the call. This “middle position” of the SIP server allows
the system to execute difficult call scenarios, like recording a call, stepping out of the
voicemail system (by pressing 0), barging into a call, and many other call scenarios that
are very hard to do without this center position.
Answering
SIP UA
Originating
SIP UA
Originating
SIP Endpoint
Answering
SIP Endpoint
Figure B-2. Back-to-Back User Agent (B2BUA)