Routing and emergency numbers

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Emergency calling is disabled in SatSite units by default because the configuration must be well tested and this is a risky operation.

GSM phones never send out the dialled emergency number. Instead, they make a special emergency call in which some (but not all) phones may add extra information, such as the desired service (police, etc.).

There are 4 sources of numbers that are interpreted as emergency:

- 112 is GSM standard and cannot be turned off
- other numbers added in firmware by the phone manufacturer, such as 911 or other regional numbers; these also cannot be turned off
- optional emergency numbers provided by the SIM (if present)
- optional emergency numbers added by the network after a successful registration if the SIM is accepted

The configuration of YateBTS / NiPC allows routing emergency calls somewhere. If not configured, they will be routed like other calls to the outbound with called party "sos" (that is, sip:sos@domain.name)

Custom emergency calls routing is configured by the gw_sos parameter in section [general] of subscribers.conf, and may look like:

; Route to an arbitrary protocol and gateway
gw_sos=sip/sip:sos@emergency.gw
; Redirect to a short number
gw_sos=111
; Redirect to an international format number
gw_sos=+10744341111

The redirect to number format allows routing emergency calls to a local subscriber's short number or MSISDN.

Depending on if and where the phone was attached when making the emergency call the IMSI and phone number may not be present, in this case the calling party identity is based on IMEI:

From: <sip:IMEIxxxxxxxxxxxxxx@ip.add.re.ss>

Prioritization is not implemented, other calls are not preempted.