Pre-empting Existing Calls for E911 IP-to-Tel Calls
If the device receives an emergency call (E911) from the IP network destined to the Tel and there are unavailable channels (e.g., all busy), the device terminates one of the current calls (arbitrary) and then sends the emergency call to that channel. The preemption is done only on a channel belonging to the same Trunk Group for which the emergency call was initially destined and if the 'Channel Select Mode' parameter (ChannelSelectMode) is configured with a value other than By Dest Phone Number (0). Call preemption is done only if the incoming IP-to-Tel call is identified as an emergency call.
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To configure call preemption for emergency calls: |
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1.
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Enable call preemption for emergency calls: |
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For all calls: Open the Priority & Emergency page (Setup menu > Signaling & Media tab > SIP Definitions folder > Priority and Emergency), and then from the 'Call Priority Mode' drop-down list (CallPriorityMode), select Emergency: |
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For specific calls: Open the Tel Profiles table (see Configuring Tel Profiles), and then for the required Tel Profile, configure the 'Call Priority Mode' drop-down list (TelProfile_CallPriorityMode) to Emergency. |
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2.
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Configure the [EmergencyCallAlertInfoUri] parameter with a value that if the SIP Alert-Info header in the incoming INVITE message contains the same value, then the INVITE is considered an emergency call. If not configured, the call is not considered an emergency call (even if the header is present). |
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3.
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(Optional) Block device resets that are triggered through CLI (reload command) during and after emergency calls, by configuring the [ReloadTimeoutForEmergencyCall] parameter to a non-zero value. This is the duration for blocking resets after the call has ended (regardless of whether it was successfully established or not). |
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The feature is applicable to the following interfaces: |
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The device also identifies emergency calls if the Priority header of the incoming SIP INVITE message contains the “emergency” value. |
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For Trunk Groups configured with call preemption, all must be configured to MLPP [1] or all configured to Emergency [2]. In other words, you cannot set some trunks to [1] and some to [2]. |
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If you are using a Tel Profile, you must configure the 'Call Priority Mode' parameter in the Tel Profile table and on the Priority & Emergency page with the same value; otherwise, the Tel Profile parameter is not applied. |
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If you configure call preemption using the global parameter and a new Tel Profile is subsequently added, the TelProfile_CallPriorityMode parameter automatically acquires the same setting as well. |
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For FXO interfaces, the preemption is done only on existing IP-to-Tel calls. In other words, if all the current FXO channels are busy with calls that were answered by the FXO device (i.e., Tel-to-IP calls), new incoming emergency IP-to-Tel calls are rejected.
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