8.21 Emergency Services

3GPP43.318Generic Access Network (GAN)Release 16Stage 2TS

8.21.1 General

The GANC can indicate, in the GAN Registration procedures, an Access Network preference for the placement of emergency calls.

Based on the Access Network preference, and if any GERAN/UTRAN coverage is available (either from the GAN subscriber’s home PLMN or from any roamer PLMN, irrespective of roamer agreements), the MS should switch from GAN mode to GERAN/UTRAN mode and place the emergency call over GERAN/UTRAN, to leverage the location determination infrastructure in GERAN/UTRAN. During the emergency call, the MS should not attempt to handover the call to GAN. After the emergency call is completed, the MS may perform normal rove-in procedures to re-enter GAN mode, if GAN coverage is still available. Alternatively there may be a penalty timer configured to ensure that the MS remains in GERAN/UTRAN for call-back purposes. On expiry of the penalty timer the MS may perform normal rove-in procedures to re-enter GAN mode, if GAN coverage is still available.

Based on the Access Network preference, or if no GERAN/UTRAN coverage is available (neither from the GAN subscriber’s home PLMN nor from any roamer PLMN, irrespective of roamer agreements), the MS places the emergency call over GAN. In GAN, the emergency call is handled just like a GSM emergency call origination. The cell ID associated with the GANC provides an indication of the location of the MS. Additionally, more accurate location information may be obtained by the GANC either directly from the MS (e.g. using AGPS) or from the generic IP access network point of attachment (e.g. using a database of IP or MAC addresses). If available, the GANC can pass this location information through BSSMAP or RANAP signalling to the core network, when requested. However, location services based on mechanisms using the GERAN/UTRAN physical layer cannot be applied.

NOTE: A mechanism may be required in the GANC to force the MS to GERAN/UTRAN mode, if the location accuracy is not deemed sufficient for emergency calls in GAN mode.

8.21.2 North American Emergency Calls

8.21.2.1 Phase 1 Solution

8.21.2.1.1 Phase 1 Requirements

Wireless service providers were required by the FCC to have the capability to send wireless 911 calls to an E911 public safety answering point (PSAP) containing two important sets of data:

1. The location of the cell tower through which the E911 call was processed.

2. The mobile directory number (MDN) or "call back number" of the wireless phone placing the 911 call.

8.21.2.1.2 Phase 1 Mechanism

The GANC shall indicate during registration, when entering GAN mode, whether GERAN/UTRAN or GAN is preferred for support of emergency calls.

– If GAN mode is the preferred emergency call mode, the emergency call shall be placed over GAN if the mobile is in GAN mode. The GANC can reject the call depending on operator policy.

– If GERAN/UTRAN mode is the preferred emergency mode, the emergency call shall be placed over the GERAN/UTRAN when a GERAN/UTRAN network is available. If a GERAN/UTRAN network is not available the emergency call shall be placed over GAN.

8.21.2.2 Phase 2 Solution

8.21.2.2.1 Phase 2 Requirements

Wireless service providers are required by the FCC to have the ability to provide the actual caller’s location to the E911 PSAP. The location accuracy requirements differ depending on whether a network-based or handset-based approach is chosen.

– Network-based requirement: Within 100 meters, 67% of the time and within 300 meters, 95% of the time.

– Handset-based requirement: Within 50 meters, 67% of the time and within 150 meters, 95% of the time.

The handset-based requirements apply to terminals supporting location determining mechanisms (e.g. A-GPS, E-OTD). This may require new, modified or upgraded terminals.

8.21.2.2.2 Phase 2 Mechanism

The emergency call is placed over GERAN/UTRAN or GAN. If the emergency call is placed over GAN, the GANC will need to provide accurate location information for the MS or the AP through which the MS is placing the emergency call. This can be done in a number of ways:

– the GANC can reference an AP-ID to location mapping database for the GAN service;

– the MS can provide its current location (e.g. obtained via AGPS) in GA-RC REGISTER REQUEST/UPDATE message;

– the GANC can reference an MS (public) IP address to location mapping database;

– the GANC can deliver the required location information to the SMLC via Lb interface and the SMLC is responsible for final location determination.

The GANC passes this location information through BSSMAP or RANAP signalling to the CN, when requested.