AudioCodes Mediant 3000 User Manual page 550

Thus, the Stateful Proxy mode provides full SIP transparency (no topology hiding) or
asymmetric topology hiding. Below is an example of a SIP dialog-initiating request when
operating in Stateful Proxy mode for full transparency, showing all the incoming SIP
headers retained in the outgoing INVITE message.
Figure 28-1: Example of SIP Message Handling in Stateful Proxy Mode
Some of the reasons for implementing Stateful Proxy mode include:

B2BUA typically hides certain SIP headers for topology hiding. In specific setups,
some SIP servers require the inclusion of these headers to know the history of the SIP
request. In such setups, the requirement may be asymmetric topology hiding, whereby
SIP traffic toward the SIP server must expose these headers whereas SIP traffic
toward the users must not expose these headers.

B2BUA changes the call identifiers between the inbound and outbound SBC legs and
therefore, call parties may indicate call identifiers that are not relayed to the other leg.
Some SIP functionalities are achieved by conveying the SIP call identifiers either in
SIP specific headers (e.g., Replaces) or in the message bodies (e.g. Dialog Info in an
XML body).

In some setups, the SIP client authenticates using a hash that is performed on one or
more of the headers that B2BUA changes (removes). Therefore, implementing B2BUA
would cause authentication to fail.

For facilitating debugging procedures, some administrators require that the value in
the Call-ID header remains unchanged between the inbound and outbound SBC legs.
As B2BUA changes the Call-ID header, such debugging requirements would fail.
The operating mode can be configured per the following configuration entities:

SRDs in the SRD table (see ''Configuring SRDs'' on page 326)

IP Groups in the IP Group table (see ''Configuring IP Groups'' on page 343)
If the operation mode is configured in both tables, the operation mode of the IP Group is
applied. Once configured, the device uses default settings in the IP Profile table for
handling the SIP headers, as mentioned previously. However, you can change the default
settings to enable partial transparency.
User's Manual 550
Mediant 3000
Document #: LTRT-89730