If all the ELINs in the list are in use by active calls, the ELIN Gateway selects the ELIN
number as follows:
1. The ELIN with the lowest count (i.e., lowest number of active calls currently using
this ELIN).
2. If the count between ELINs is identical, the ELIN Gateway selects the ELIN with
the greatest amount of time passed since the original E9-1-1 call using this ELIN
was terminated with the PSAP. For example, if E9-1-1 caller using ELIN
4257275678 was terminated at 11:01 and E9-1-1 caller using ELIN 4257275670
was terminated at 11:03, then the ELIN Gateway selects ELIN 4257275678.
In this scenario, multiple E9-1-1 calls will be sent with the same ELIN.
28.11.4.3.5 Location Based Emergency Routing
The device supports location-based emergency routing (E-911) in Lync Server 2010. This
ensures that E-911 calls from remote branches are routed to emergency providers that are
relevant to the geographical area in which the remote branch callers are physically located.
To support this, the device enables routing and SIP header / number manipulation of such
emergency calls based on the geographical location of the caller. The device manipulates
the received destination number (i.e., 911) from the remote branch callers, into a
destination number of an emergency provider that is relevant to the geographical area in
which the remote branch office is located.
28.11.4.4 Configuring AudioCodes ELIN Gateway
This section describes E9-1-1 configuration of the AudioCodes ELIN Gateway deployed in
the Lync Server 2010 environment.
28.11.4.4.1 Enabling the E9-1-1 Feature
By default, the E9-1-1 feature in the ELIN Gateway for Lync Server 2010 is disabled. To
enable it, the following ini file parameter setting must be done:
E911Gateway = 1
28.11.4.4.2 Configuring the E9-1-1 Callback Timeout
The PSAP can use the ELIN to call back the E9-1-1 caller within a user-defined time
interval (in minutes) from when the initial call established with the PSAP has been
terminated. By default, an ELIN can be used for PSAP callback within 30 minutes after the
call is terminated. You can change this interval, by using the following ini file parameter:
E911CallbackTimeout = <time value> ; where <time value > can be
any value from 0 through 60
28.11.4.4.3 Configuring the SIP Release Cause Code for Failed E9-1-1 Calls
When a Lync 2010 client makes an emergency call, the call is routed through the Microsoft
Mediation Server to the ELIN Gateway, which sends it on to the PSTN. In some scenarios,
the call may not be established due to either the PSTN (for example, the destination is
busy or not found) or ELIN Gateway (for example, lack of resources or an internal error). In
such a scenario, the Mediation Server requires that the ELIN Gateway "reject" the call with
the SIP release cause code 503 "Service Unavailable" instead of the designated release
call. Such a release cause code enables the Mediation Server to issue a failover to another
entity (for example, another ELIN Gateway), instead of retrying the call or returning the
release call to the user.
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