Emergency Calling in WebRTC

Problem description.

Bring your own number (BYON) service aims to provide consumers with the ability to use their phone number (MSISDN) for outgoing and incoming calls from non-SIM card or non-cellular devices. Any web-based application can integrate this BYON as a feature utilizing well-known HTTP and webRTC technologies.To access the service, users are required to authenticate using their digital credentials associated with their Internet Service Provider account, for example their operator app credentials. Registration from a web endpoint is necessary to enable the service on these devices.

The regulator entities in many countries requires that for any voice call service, the emergency call service must be available, which implies knowing the location of the user who is making a call.

Knowing the service provided and the regulation of emergency calls. The problem is as follows. A user links his device (Tablet, XR glasses...) with his phone number thanks to BYON.  the user may leave their phone (containing the SIM) at home and goes away with the BYON device (e.g. tablet. No SIM). If this user makes an emergency call, there migh be issues to know their location.

It is necessary to find a solution to locate the above-mentioned devices. This document aims to solve Issue#25 of the WebRTC CAMARA Group

Scenarios.

Introduction:

Regarding the following scenarios. The identification of the user's location cannot be done through the MSISDN parameter. This parameter is unknown in any of the scenarios.

It is therefore proposed to identify the user's location by IP address. The IP address is a private parameter and it is necessary to obtain a public IP through NAT algorithms (CGNAT converts private IP to public IP following an algorithm).

The deterministic NAT algorithm is the one that best fits our needs. From a developer's public IP, the customer's private IP can be located on the BNG or FTTH.

1.User calls from BYON device connected to cellular network

In the 5G standard architectures the Access and Mobility Management function (AMF) is the element in charge of managing the UE mobility within the different gNodeBs of the operator. This information of the radio cell a user is connected to, is sent to the UDM throughout the N8 interface as outlined in the 3GPP standard. However, this information is also needed by the SMF to determine the best UPF the user can connect to, this is done through the N11 interface.

In this case, the user is using BYON from his cell phone connected to the cellular network. The device has its own SIM. It is possible to locate the cell to which the user is connected.

• If the user is making a call from a mobile phone with multisim capability, the antenna location described above may not work.
  Multisim enabled devices have a primary SIM and a secondary SIM with a different phone number. The user only appreciates that there is one SIM (with a single phone number).

• The localization in multisim scenario should be checked.

2. User calls from the BYON device connected to his home wifi

The user makes a call from a device using BYN. The user is connected to the Wifi network at home.  The operator can usually determine the connection originated from the home connection point.
The subscriber's address is known.

3. User calls from BYON device connected to a different wifi than home wifi (eg. starbucks)

In this scenario the user is using the BYON service on a device that does not have a SIM (cannot be located). The user's devices is also connected to a Wifi network other than his home network (Eg: Wifi network of a coffee shop).

This case is the most difficult to solve

Since the user's device could be mobile, to differentiate between scenarios 2 and 3, we need the user to confirm whether they are at their registered emergency address. If they are, PSAP routing will be based on that address. If they are not, the emergency call will be routed to the national emergency center. Note: The logic for confirming the registered address could potentially be used when the user is on a cellular network and the BYON App/Service does not have access to the device's location using the cellular network.

4. User calls from BYON device (Mobile phone) that can provide device location (and user has provided permission to fetch location) 

In this scenario, the user is utilizing the BYON service on a device (mobile phone) that allows the BYON app to access the device's location. If the user has granted location access permission, the emergency call will be placed with the device's location, and PSAP routing will be based on both the device location and the registered emergency address. If the device does not support location access or if the user has not granted permission, it will revert to scenario 2 or 3.