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Sip - B2bua

A back-to-back user agent (B2BUA) is a logical network element in SIP that receives SIP requests, modifies them, and forwards them as new requests. Unlike proxies, B2BUAs maintain dialog state and must participate in all requests within a dialog. B2BUAs break the end-to-end nature of SIP by operating as both the user agent client and server between two endpoints of a call. They implement functions like call management, network interworking, and hiding of network details. Common examples of B2BUAs include private branch exchange phone systems and session border controllers.

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93 views2 pages

Sip - B2bua

A back-to-back user agent (B2BUA) is a logical network element in SIP that receives SIP requests, modifies them, and forwards them as new requests. Unlike proxies, B2BUAs maintain dialog state and must participate in all requests within a dialog. B2BUAs break the end-to-end nature of SIP by operating as both the user agent client and server between two endpoints of a call. They implement functions like call management, network interworking, and hiding of network details. Common examples of B2BUAs include private branch exchange phone systems and session border controllers.

Uploaded by

VISHAL KUMAR
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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3/10/23, 1:45 PM SIP - B2BUA

SIP - B2BUA

A back-to-back user agent (B2BUA) is a logical network element in SIP applications. It is a type of
SIP UA that receives a SIP request, then reformulates the request, and sends it out as a new
request.

Unlike a proxy server, it maintains dialog state and must participate in all requests sent on the
dialogs it has established. A B2BUA breaks the end-to-end nature of SIP.

B2BUA – How it Works?


A B2BUA agent operates between two endpoints of a phone call and divides the communication
channel into two call legs. B2BUA is a concatenation of UAC and UAS. It participates in all SIP
signalling between both ends of the call, it has established. As B2BUA available in a dialog service
provider may implement some value-added features.

In the originating call leg, the B2BUA acts as a user agent server (UAS) and processes the request
as a user agent client (UAC) to the destination end, handling the signalling between end points
back-to-back.

A B2BUA maintains the complete state for the calls it handles. Each side of a B2BUA operates as a
standard SIP network element as specified in RFC 3261.

Functions of B2BUA
A B2BUA provides the following functions −

Call management (billing, automatic call disconnection, call transfer, etc.)

Network interworking (perhaps with protocol adaptation)


Hiding of network internals (private addresses, network topology, etc.)

Often, B2BUAs are also implemented in media gateways to bridge the media streams for full control
over the session.

Example of B2BUA
Many private branch exchange (PBX) enterprise telephone systems incorporate B2BUA logic.

Some firewalls have built in with ALG (Application Layer Gateway) functionality, which allows a
firewall to authorize SIP and media traffic while still maintaining a high level of security.

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3/10/23, 1:45 PM SIP - B2BUA

Another common type of B2BUA is known as a Session Border Controller (SBC).

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