AudioCodes Mediant 4000 SBC, User Manual

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CHAPTER 28 Advanced SBC Features
Mediant 4000 SBC | User's Manual
2. Enable the E9-1-1 feature, by configuring the 'PSAP Mode' parameter to PSAP Server in the
IP Groups table for the IP Group of the PSAP server (see Enabling the E9-1-1 Feature ).
3. Configure routing rules in the IP-to-IP Routing table for routing between the emergency callers'
IP Group and the PSAP server's IP Group. The only special configuration required for the
routing rule from emergency callers to the PSAP server:
● Configure the emergency number (e.g., 911) in the 'Destination Username Pattern' field.
● Assign the Call Setup rule that you configured for obtaining the ELIN number from the AD
(see Step 1) in the 'Call Setup Rules Set ID' field (see
Configuring SBC IP-to-IP Routing
Rule for E9-1-1 ).
Configuring Dual Registration for SIP Entity
Some SIP entities (e.g., IP Phones) are setup to register with two registrar/proxy servers (primary
and secondary). The reason for this is to provide call redundancy for the SIP entity in case one of
the proxy servers fail. When the SIP entity registers with the proxy servers, it 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: 172.17.0.1.20:5060
● 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").
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