AudioCodes Mediant 500L MSBR User Manual

User's Manual 31. SBC Overview
Version 6.8 527 Mediant 500L MSBR
The handling of SIP 3xx can be configured for all calls, using the global parameter
SBC3xxBehavior. For configuring different SIP 3xx handling options for different UAs (i.e.,
per IP Group), use the IP Profile table parameter, 'SBC Remote 3xx Behavior'.
31.7.1.1 Resultant INVITE Traversing Device
The device can handle SIP 3xx responses so that the new INVITE message sent as a
result of the 3xx traverses the device. The reasons for enforcing resultant INVITEs to
traverse the device may vary:

The user that receives the 3xx is unable to route to the 3xx contact (i.e., the user is on
the LAN and the new contact is on the WAN). In such a scenario, the device enables
the user to reach the WAN contact and overcome NAT problems.

Enforce certain SBC policies (e.g., call admission control, header manipulation, and
transcoding) on the resultant INVITE.
The device enforces this by modifying each Contact in the 3xx response as follows:

Changes the host part to the device's IP address – this change causes the remote
user agent to send the INVITE to the device.

Adds a special prefix ("T~&R_") to the Contact user part – to identify the new INVITE
as a 3xx resultant INVITE.
The SBC handling for the 3xx resultant INVITE is as follows:
1. The incoming INVITE is identified as a 3xx resultant INVITE according to the special
prefix.
2. The device automatically replaces the SBC host part (in the Request-URI) with the
host from the 3xx Contact.
3. The prefix ("T~&R_") remains in the user part for the classification, manipulation, and
routing mechanisms.
4. The classification, manipulation, and routing processes are done exactly like any other
INVITE handling. The special prefix can be used for specific routing rules for 3xx
resultant INVITEs.
5. The prefix is removed before the resultant INVITE is sent to the destination.
Figure 31-5: SIP 3xx Response Handling
The process of this feature is described using an example:

AudioCodes Mediant 500L MSBR Specifications

General

Brand	AudioCodes
Model	Mediant 500L MSBR
Category	Network Router
Language	English