Version 7.2 317 Mediant 800B Gateway & E-SBC
User's Manual 15. Services
15.8.4.2 Configuring the E9-1-1 Callback Timeout
The PSAP can use the ELIN to call back the E9-1-1 caller within a user-defined time interval (in
minutes) from when the initial call established with the PSAP has been terminated. By default, an
ELIN can be used for PSAP callback within 30 minutes after the call is terminated. You can
change this to any value between 0 and 60:
To configure the E9-1-1 callback timeout
1. Open the Priority & Emergency page (Setup menu > Signaling & Media tab > SIP
Definitions folder > Priority and Emergency).
2. In the 'E911 Callback Timeout' field (E911CallbackTimeout), enter the required callback
timeout.
Figure 15-58: Configuring E9-1-1 Callback Timeout
3. Click Apply.
15.8.4.3 Configuring the SIP Release Cause Code for Failed E9-1-1 Calls
When a Skype for Business client makes an emergency call, the call is routed through the
Microsoft Mediation Server to the ELIN device, which sends it on to the PSTN. In some
scenarios, the call may not be established due to either the destination (for example, busy or not
found) or the ELIN device (for example, lack of resources or an internal error). In such a scenario,
the Mediation Server requires that the ELIN device "reject" the call with the SIP release cause
code 503 "Service Unavailable" instead of the designated release call. Such a release cause
code enables the Mediation Server to issue a failover to another entity (for example, another
ELIN device), instead of retrying the call or returning the release call to the user.
To support this requirement, you can configure the ELIN device to send a 503 "Service
Unavailable" release cause code instead of SIP 4xx if an emergency call cannot be established:
To enable SIP response 503 upon failed E911:
1. Open the Advanced Parameters page (Setup menu > Signaling & Media tab > Gateway
folder > Gateway Advanced Parameters).
2. From the 'Emergency Special Release Cause' drop-down list
(EmergencySpecialReleaseCause), select Enable.
Figure 15-59: Configuring SIP Release Code for Failed E9-1-1 Calls
3. Click Apply.
Note: The feature is applicable only to the Gateway application (digital interfaces).
15.8.4.4 Configuring SBC IP-to-IP Routing Rule for E9-1-1
To route incoming E9-1-1 calls to the emergency service provider's PSAP server, you need to
configure routing rules in the IP-to-IP Routing table for routing between the emergency callers' IP
Group and the PSAP server's IP Group. The only special configuration is to define the emergency
number (e.g., 911) in the 'Destination Username Prefix' parameter of the IP Group belonging to
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