AudioCodes E-SBC User Manual page 783

CHAPTER 30 SBC Overview
■ 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.
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).
2. The device replaces the Contact header value with the special prefix and database key value
as user part, and with the device's URL as host part (e.g., Contact: <sip:Prefix_Key_User-
@SBC:5070;transport=udp>;q=0.5).
3. The device sends this manipulated SIP 3xx response to the Far-End User (FEU).
4. The FEU sends a new request with the Request-URI set to the value of the received 3xx
response's Contact header (e.g., RequestURI: sip:Prefix_Key_
User@SBC:5070;transport=udp).
5. Upon receipt of the new request from the FEU, the device replaces the Request-URI with the
new destination address (e.g., RequestURI: sip:Prefix_User-
@IPPBX:5070;transport=tcp;param=a).
6. The device removes the user prefix from the Request-URI, and then sends this Request-URI
to the new destination (e.g., RequestURI: sip:User@IPPBX:5070;transport=tcp;param=a).
Mediant 1000 Gateway & E-SBC | User's Manual
- 745 -