Selecting Elin For Multiple Calls Within Same Erl - AudioCodes Mediant 1000 User Manual

User's Manual
number (i.e., ELIN) received from the PSAP to the corresponding E9-1-1 caller's extension
number as matched in the ELIN table.
The handling of PSAP callbacks by the device is as follows:
1. When the device receives a call from the emergency service provider, it searches the
ELIN table for an ELIN that corresponds to the received called party number in the
incoming message.
2. If a match is found in the ELIN table, it routes the call to the Mediation Sever by
sending a SIP INVITE, where the values of the To and Request-URI are taken from
the value of the original From header that is stored in the ELIN table (in the Call From
column).
3. The device updates the Time in the ELIN table. (The Count is not affected).
The PSAP callback can be done only within a user-defined period (see ''Configuring the
E9-1-1 Callback Timeout'' on page 291), started from after the original E9-1-1 call
established with the PSAP is terminated. After this time expires, the table entry with its
ELIN is disregarded and no longer used (for PSAP callback). Therefore, table entries of
only the most recently terminated E9-1-1 callers are considered in the ELIN table. If the
PSAP callback is done after this timeout expires, the device is unable to route the call to
the E9-1-1 caller and instead, either sends it as a regular call or most likely, rejects it if
there are no matching routing rules. However, if another E9-1-1 caller has subsequently
been processed with the same ELIN number, the PSAP callback is routed to this new E9-
1-1 caller.
In scenarios where the same ELIN number is used by multiple E9-1-1 callers, upon receipt
of a PSAP callback, the device 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 device sends it to
the E9-1-1 caller with phone number "4258359555".
ELIN
4257275678
4257275678
4257275678

15.7.3.4 Selecting ELIN for Multiple Calls within Same ERL

The device 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 device sends
the ELIN number as the E9-1-1 calling number to the emergency service provider. If the
XML message contains more than one ELIN number, the device 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 device 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 device selects the ELIN number
as follows:
1. The ELIN with the lowest count (i.e., lowest number of active calls currently using
this ELIN).
Version 7.2
Table 15-26: Choosing Caller of ELIN
Time
11:00
11:01
11:03
289
Call From
4258359333
4258359444
4258359555
Mediant 1000B Gateway & E-SBC
15. Services