AudioCodes Mediant 500 MSBR, Руководство пользователя

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Version 7.2 645 Mediant 500 MSBR
User's Manual 32. SBC Overview
32.8.1.1 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) 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 32-6: SIP 3xx Response Handling
The process of this feature is described using an example:
1. The device receives the Redirect server's SIP 3xx response (e.g., Contact:
<sip:User@IPPBX:5060;transport=tcp;param=a>;q=0.5).