AudioCodes Mediant 4000 SBC User Manual page 574

sends two identical REGISTER messages - one to the primary proxy and one to the
secondary proxy. When the device is located between the SIP entity and the two proxy
servers, it needs to differentiate between these two REGISTER messages even though
they are identical. This is crucial to ensure that the device forwards the two registrations to
the proxy servers and that the device performs correct call routing between the SIP entity
and the two proxy servers.
To differentiate between these REGISTER messages, a unique SIP Interface needs to be
used for each REGISTER message. Each REGISTER message is registered in the
registration database using a unique "ac-int=<value>" string identifying the SIP Interface for
the Contact user. In addition, for SIP requests (e.g., INVITE) from the proxy servers, the
device needs to search its registration database for the contact user so that it can forward it
to the user. In normal registration, the host part of the Request-URI contains the IP address
of the device and therefore, there is no way of knowing which registered user the INVITE is
intended for. To overcome this issue, you can configure the device to use a special string
with a unique value, "ac-feu=<value>" for each registration, allowing the device to
differentiate between two registrations from the same user (identical REGISTER requests).
Each REGISTER message is registered in the registration database using the unique "ac-
feu=" string identifier for the Contact user.
A summary of how the device registers the two REGISTER messages in its registration
database is as follows:
1. The addresses of the proxy servers that are configured on the SIP entity (IP Phone)
must be the device's IP address with a different SIP local port for each one, for
example:
•
Primary Proxy Server: 172.17.0.1:5060
•
Secondary Proxy Server: 172.17.0.1:5080
2. When the device receives two identical REGISTER messages from the SIP entity, it
differentiates them by the SIP port on which they are received. The port allows the
device to associate them with a SIP Interface (5060 for "Interface-1" and 5080 for
"Interface-2").
3. The device performs SIP message manipulation (Pre-classification Manipulation) on
the REGISTER messages to add a special parameter ("ac-int=<value>") to the
Contact header to identify the SIP Interface on which each message is received. For
example:
•
REGISTER for Primary Proxy received on SIP Interface "Interface-1":
REGISTER
To: sip:100@audc.com
Contact: <sip:100@172.17.100.20;ac-int=1>
•
REGISTER for Secondary Proxy received on SIP Interface "Interface-2":
REGISTER
To: sip:100@audc.com
Contact: <sip:100@172.17.100.20;ac-int=2>
4. The device adds to the Contact header a special string with a unique value, "ac-
feu=<value>" for each registration (e.g., "Contact: <sip:100@172.17.100.20;ac-
int=1;ac-feu=x>").
5. The device saves the two contacts (100@172.17.100.20;ac-int=1;ac-feu=x and
100@172.17.113.32;ac- int=2;ac-feu=y) under the same AOR (100@audc.com) in its
user registration database.
The SIP call flow for dual registration is shown below:
User's Manual 574
Mediant 4000 SBC
Document #: LTRT-40203