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 SIP domain; this requires the manual configuration
of
of
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
Go to Applications > B2BUA > B2BUA TURN servers to enter details of the TURN servers that are needed by the
Expressway B2BUA instances. The page lists the currently configured TURN servers and lets you create, edit and
delete them.
Expressway B2BUA instances. The page lists the currently configured TURN servers and lets you create, edit and
delete them.
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.
subzone.
If you want to use the TURN servers for Microsoft interoperability, you must enable Offer TURN services (See
).
Field
Description
TURN server address
The IP address of a TURN server to offer when establishing ICE calls (for example, with a
Microsoft Edge server).
Microsoft Edge server).
The TURN server must be RFC 5245 compliant, for example an Expressway-E TURN
server.
server.
TURN server port
The listening port on the TURN server. Default is 3478.
Description
A free-form description of the TURN server.
TURN services
username and
password
password
The username and password that are required to access the TURN server.
Table 14 TURN Server Configuration Details
If you are using the TURN server on a Large Expressway-E, it listens on all ports in the range 3478-3483 by default.
You can enter the same TURN server address up to six times if you supply a different port each time, to make the best
use of the Large Expressway-E's capacity.
You can enter the same TURN server address up to six times if you supply a different port each time, to make the best
use of the Large Expressway-E's capacity.
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Cisco Expressway Administrator Guide
Applications