Pre-Empting Existing Calls For E9-1-1 Calls; Psap Callback To Skype For Business Clients For Dropped E9-1-1 Calls - AudioCodes Mediant 4000 SBC User Manual

User's Manual
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15.8.3.2 Pre-empting Existing Calls for E9-1-1 Calls

If the ELIN device receives an E9-1-1 call from the IP network and there are unavailable
channels (for example, all busy), the device immediately terminates one of the non-E9-1-1
calls (arbitrary) and accepts the E9-1-1 call on the freed channel:

The preemption is done only on a call pertaining to the same source IP Group from
which the E9-1-1 call is received, or the same destination IP Group (i.e., PSAP
Server).
This feature is initiated only if the received SIP INVITE message contains a Priority header
set to "emergency", as shown below:
PRIORITY: emergency

15.8.3.3 PSAP Callback to Skype for Business Clients for Dropped E9-1-1 Calls

As the E9-1-1 service automatically provides all the contact information of the E9-1-1 caller
to the PSAP, the PSAP operator can call back the E9-1-1 caller. This is especially useful in
cases where the caller disconnects prematurely. However, as the Enterprise sends ELINs
to the PSAP for E9-1-1 calls, a callback can only reach the original E9-1-1 caller using the
device to translate the ELIN number back into the E9-1-1 caller's extension number.
In the ELIN table of the device, the temporarily stored From header value of the SIP
INVITE message originally received from the E9-1-1 caller is used for PSAP callback.
When the PSAP makes a callback to the E9-1-1 caller, the device translates the called
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
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