User's Manual 468 Document #: LTRT-10466
Mediant 500L MSBR
In scenarios where the same ELIN number is being used by multiple E9-1-1 callers, upon
receipt of a PSAP callback, the ELIN Gateway sends the call to the most recent E9-1-1
caller. For example, if the ELIN number "4257275678" is being used by three E9-1-1
callers, as shown in the table below, then when a PSAP callback is received, the ELIN
Gateway sends it to the E9-1-1 caller with phone number "4258359555".
Table 29-5: Choosing Caller of ELIN
ELIN Time Call From
4257275678 11:00 4258359333
4257275678 11:01 4258359444
4257275678 11:03
4258359555
29.11.4.3.4 Selecting ELIN for Multiple Calls within Same ERL
The ELIN Gateway supports the receipt of up to five ELIN numbers in the XML message of
each incoming SIP INVITE message. As discussed in the preceding sections, the ELIN
Gateway sends the ELIN number as the E9-1-1 calling number to the PSTN-based
emergency provider. If the XML message contains more than one ELIN number, the ELIN
Gateway chooses the ELIN according to the following logic:
If the first ELIN in the list is not being used by other active calls, it chooses this ELIN.
If the first ELIN in the list is being used by another active call, the ELIN Gateway skips
to the next ELIN in the list, and so on until it finds an ELIN that is not being used and
sends this ELIN.
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.
29.11.4.3.5 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.
For an example on location-based emergency call routing, see ''Configuring Location-
Based Emergency Routing'' on page 470.
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