AudioCodes Mediant 500 MSBR, User Manual

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Version 7.2 279 Mediant 500 MSBR
User's Manual 18. Services
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 280), 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".
Table 18-22: Choosing Caller of ELIN
ELIN Time Call From
4257275678 11:00 4258359333
4257275678 11:01 4258359444
4257275678 11:03 4258359555
18.7.3.4 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).
2. If the count between ELINs is identical, the device 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 4257
2 75678
was terminated at 11:01 and E9-1-1 caller using ELIN 425727567 0 was
terminated at 11:03 , then the device selects ELIN 425727567 8 .
In this scenario, multiple E9-1-1 calls are sent with the same ELIN.