B2Bua And Stateful Proxy Operating Modes - AudioCodes Mediant 4000 SBC User Manual

CHAPTER 22 SBC Overview
● Generates a new SIP Call-ID header value (different between legs).
● Changes the SIP Contact header and sets it to the device's address.
● Layer-3 topology hiding by modifying source IP address in the SIP IP header.
■ SIP normalization: The device supports SIP normalization, whereby the SBC application can
overcome interoperability problems between SIP user agents. This is achieved by the
following:
● Manipulation of SIP URI user and host parts.
● Connection to ITSP SIP trunks on behalf of an IP-PBX - the device can register and utilize
user and password to authenticate for the IP-PBX.
■ Survivability:
● Routing calls to alternative routes such as the PSTN.
● Routing calls between user agents in the local network using a dynamic database (built
according to registrations of SIP user agents).
■ Routing:
● IP-to-IP routing translations of SIP, UDP, TCP, TLS (when extensive transcoding is not
required).
● Load balancing and redundancy of SIP servers.
● Routing according to Request-URI\Specific IP address\Proxy\FQDN.
● Alternative routing.
● Routing between different Layer-3 networks (e.g., LAN and WAN).
■ Load balancing\redundancy of SIP servers.
■ ITSP accounts.
■ SIP URI user and host name manipulations.
■ Coder transcoding.

B2BUA and Stateful Proxy Operating Modes

The device can operate in one or both of the following SBC modes:
■ Back-to-Back User Agent (B2BUA): Maintains independent sessions toward the endpoints,
processing an incoming request as a user agent server (UAS) on the inbound leg, and
processing the outgoing request as a user agent client (UAC) on the outbound leg. SIP
messages are modified regarding headers between the legs and all the device's interworking
features may be applied.
■ Stateful Proxy Server: SIP messages traverse the device transparently (with minimal
interference) between the inbound and outbound legs, for connecting SIP endpoints.
By default, the device's B2BUA mode changes SIP dialog identifiers and topology data in SIP
messages traversing through it:
■ Call identifiers: Replaces the From-header tag and Call-ID header so that they are different for
each leg (inbound and outbound).
■ Routing headers:
● Removes all Via headers in incoming requests and sends the outgoing message with its
own Via header.
● Doesn't forward any Record-Route headers from the inbound to outbound leg, and vice
versa.
● Replaces the address of the Contact header in the incoming message with its own
address in the outgoing message.
■ Replaces the User-Agent/ Server header value in the outgoing message, and replaces the
original value with itself in the incoming message.
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Mediant 4000 SBC | User's Manual