Cisco Cisco Expressway Maintenance Manual
B2BUA (Back-to-Back User Agent) Overview
A B2BUA operates between both endpoints of a SIP call and divides the communication channel into two
independent call legs. Unlike a proxy server, the B2BUA maintains complete state for the calls it handles. Both legs of
the call are shown as separate calls on the Call status and Call history pages.
independent call legs. Unlike a proxy server, the B2BUA maintains complete state for the calls it handles. Both legs of
the call are shown as separate calls on the Call status and Call history pages.
B2BUA instances are hosted on the Expressway. They are used in the following scenarios:
■
; this usage does not require any explicit B2BUA configuration
■
required to support ICE calls
■
to route SIP calls between the Expressway and a Microsoft Edge Server; this requires the manual configuration
of the
of the
available for use by the B2BUA
Note:
The B2BUA does not use or preserve DSCP information (Differentiated Services Code Point) from incoming
traffic. It does not apply DSCP information to outgoing traffic.
Configuring B2BUA TURN Servers
The B2BUA TURN servers page (Applications > B2BUA > B2BUA TURN servers) is used to configure the set of
TURN servers available for use by a B2BUA instance. The page lists all the currently configured TURN servers and lets
you create, edit and delete TURN servers.
TURN servers available for use by a B2BUA instance. The page lists all the currently configured TURN servers and lets
you create, edit and delete TURN servers.
The B2BUA chooses which TURN server to offer via random load-balancing between all of the available servers.
There is no limit to the number of servers that can be configured for the B2BUA to choose from.
There is no limit to the number of servers that can be configured for the B2BUA to choose from.
for a zone.
The configurable options are:
Field
Description
Usage tips
TURN server address
The IP address of a TURN server to offer when
establishing ICE calls (for example, with a
Microsoft Lync Edge server).
establishing ICE calls (for example, with a
Microsoft Lync Edge server).
The TURN server must be RFC 5245
compliant, for example an Expressway-E
TURN server.
compliant, for example an Expressway-E
TURN server.
TURN server port
The listening port on the TURN server. Default
is 3478.
is 3478.
Description
A free-form description of the TURN server.
TURN services
username and
username and
password
The username and password that are required
to access the TURN server.
to access the TURN server.
If the TURN server is running on a Large Expressway-E, you can make use of its scaling capabilities by specifying
additional address/port combinations.
additional address/port combinations.
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Cisco Expressway Administrator Guide
Applications