# Emergency Calling Overview

Before you configure emergency calling, it helps to understand what the service does, what it needs to work, and how location information reaches emergency responders. This page covers the prerequisites, the difference between basic and enhanced emergency service, and the key location terms used throughout the setup guides.

## What you need first

Two things must be in place before anyone can place an emergency call through Cloud Voice:

- Each IP phone or softphone that will be used must be registered to Cloud Voice.
- At least one trunk must be configured to carry the emergency number. (A trunk is the connection between Cloud Voice and the outside phone network that the call travels over.)

:::caution
Both items above are required. If a phone is not registered, or if no trunk is set up to carry the emergency number, an emergency call from that device will not reach responders. Confirm both are in place before relying on the system for emergency dialing.
:::

## Basic emergency calling

Basic emergency service routes the caller to their local Public Safety Answering Point (PSAP) but sends no location data along with the call. Because responders receive nothing about where the caller is, the caller has to state their location out loud. The PSAP then dispatches the appropriate response based on what the caller tells them.

To turn this on, see [Set up Basic Emergency Calling](/pbx/administrator-guide/set-up-basic-emergency-calling/).

## Enhanced emergency calling

Enhanced emergency service adds automatic location delivery, so the PSAP can identify where the caller is directly from the number the call arrives on, without waiting for the caller to describe it.

This service is offered only in certain countries and regions, for example E911 in North America, E112 across continental Europe, and E999 in the United Kingdom.

:::caution
For wireless IP phones and softphones such as the Cloud Voice App, the only location the PSAP receives is whatever you set as the Emergency Outbound Caller ID on the PBX. A mobile device cannot report its actual physical position, so this configured value is what determines the location shown to responders.
:::

To turn this on, see [Set up Enhanced Emergency Calling](/pbx/administrator-guide/set-up-enhanced-emergency-calling/).

## Terminology

The terms below come up repeatedly when working with enhanced emergency calling.

**PSAP (Public Safety Answering Point)**
The call center that answers emergency calls and coordinates the response, such as sending police, fire, or ambulance crews.

**ERL (Emergency Response Location)**
A precise physical location that responders can be sent to. To give the PSAP an accurate picture of where a caller is within a larger site, you can define several ERLs.

**ELIN (Emergency Location Identification Number)**
A phone number, used as the caller ID, that is tied to a specific ERL. When an emergency call goes out, the PSAP sees the ELIN and uses it to look up the matching ERL.

:::note
The ELIN also gives the PSAP a number to call back on if the emergency call drops.
:::

### Mapping ERLs to ELINs

How finely you divide a site into ERLs is up to you, and the right granularity depends on how quickly responders need to find someone. The following examples show three common approaches.

**One ERL per building**: everyone in the same building shares one ELIN.

| ELIN | ERL |
| --- | --- |
| 5085550172 | 100 Harbor Way, Building A |
| 5085550173 | 220 Harbor Way, Building B |

**One ERL per floor**: everyone on the same floor of a building shares one ELIN.

| ELIN | ERL |
| --- | --- |
| 5085550182 | 100 Harbor Way, Building A, 5th Floor |
| 5085550183 | 100 Harbor Way, Building A, 4th Floor |

**One ERL per room**: each occupant has a distinct ELIN.

| ELIN | ERL |
| --- | --- |
| 5085550192 | 100 Harbor Way, Room 3005 |
| 5085550193 | 100 Harbor Way, Room 3006 |