# Determining the location of the caller

The communication server has to determine the location of the caller (in fact it is the location of the terminal) who starts an emergency call. This location can be a building, a floor, an office or a workplace.

Dependant of the size of the communication system and the geographical spread (number of locations / buildings / offices) and the accuracy of the location required, the administrative and configuring effort can vary.

The needed configuration is dependant on the terminals type:

- IP system phones

  IP phones could be attached anywhere in the companies network, although usually they remain static on a desk. For the IP phones several configuration possibilities are available. Either you configure which location identifier shall be used for this terminal or the fall back to the location identifier of the system is used or the lookup is done based of the IP address of the terminal. This lookup can be done again in different ways. Either in the communication server is a table configured, that says which IP address range is covering which location or the IT department provides a location server, where the location identifier could be queried based on the used IP address or optionally the MAC address or even the number of the calling party.

- Mitel SIP phones

  Mitel SIP phones offer the possibility to retrieve/receive the location identifier via the LLDP protocol, if the IT department configured their switches accordingly and the switches actually support this feature. If the terminal received the location identifier, then in case the Mitel SIP terminals recognize the previously configured public emergency numbers, it fills the emergency location identifier received via the LLDP protocol into the INVITE message sent to the communication server. If the LLDP support is not working out, a Mitel SIP phones would work exactly as the IP phones.

- Standard SIP terminals

  Standard SIP terminals are treated like IP phones.

- Analogue, DSI and ISDN terminals

  Each terminal is attached to the system by fix wires. Naturally, most of these terminals will be rather close to the communication server they are connected to and therefore might share the same location identifier. Therefore should be configurable with just one entry of the location identifier in AIN node (or standalone system). However, there will be exceptions, especially if the accuracy is important. For such terminals the location identifier needs to be configurable individually.

- System DECT terminals

  System DECT terminals can roam between buildings and even sites. The communication server can determine over which System DECT radio unit the call is operating. Therefore each radio unit needs the possibility to have a location identifier, which will be used in case an emergency call is made. If all radio units are installed in the same location, then nothing needs to be configured, as there is the fallback to the AIN node setting.

- SIP-DECT terminals

  The communication server can determine the IP address of the SIP DECT radio unit. With the IP address found, the IP lookup table is consulted. There is no possibility to assign a location identifier to a SIP DECT radio unit as it is the case for System DECT radio units.

- Mobile phones with MMC and other integrated mobile/external phones

  Mobile phones with MMC and other integrated mobile/external phones are excluded from providing a location identifier. Currently there is no way to determine the location. For these terminal types no location identifier should be sent. Actually, the application on these terminals should detect the emergency call and use the mobiles native phone application to make the emergency call and therefore doesn’t use the communication server at all. The location is then determined by the mobile antennas.

- VPN connected terminals

  Any terminals connected on the other side of a VPN tunnel shall not send a location identifier, not even use the default system one. In general this would apply for terminals that are considered as nomadic and the communication server can’t be sure it is currently on the premises of the company.

- SIP networking

  Incoming calls received from other call servers, which route emergency calls via our communication server have to provide the location identifier in the incoming call. Microsoft LYNC can deliver such information. For other SIP networked communication servers the same protocol shall be applied as the communication server has to send to the provider.

- MBG teleworkers

  For teleworkers calling in via the MBG (Mitel Border Gateway), the IP lookup doesn’t make sense, as it would be always the address of the MBG. Either terminals connected via MBG have in the terminal settings their “home” emergency location identifier configured or they should suppress the sending of an emergency location identifier.

If no location identifier is defined for a terminal, the system inherits the setting from the next lower prioritized setting, as shown in the third column of the table below. In certain cases it is better to suppress the location of the calling party, this means that no location identifier shall be send out for this terminal. This is achieved by configuring an emergency location data set where the option Do not send the 'Emergency location identifier' is ticked. In such a case the call is signalled just as a normal call to the PSAP (Public safety answering point).

Table 1. Prioritization of the emergency location configurations depending on the calling terminal
Calling from... | Default location ID | Prio 1 - Prio 2 - ... - Prio x
IP system (hard) phones | Inherit | Terminal - IP lookup - system
Mitel SIP terminals, Standard SIP terminals, IP system (soft) phones, MiCollab and BluStar clients, mobile phones with MMC | Inherit | Received location ID - Terminal - AIN node - system
Analogue, DSI and ISDN terminals | Inherit | Terminal - AIN node - system
System DECT terminals | Inherit | Terminal - AIN node - system
SIP-DECT terminals | Inherit | IP lookup (of radio unit) - system
Other integrated mobile/external phones | Inherit | Terminal - system
VPN connected terminals | not applicable | not applicable
SIP networking | Inherit | Received location ID - trunk group - system
Other networking (QSIG) | Inherit | Trunk group - system
MBG teleworkers | Inherit | Terminal - IP lookup - system
Virtual terminals | not applicable | not applicable

Parent topic: Function codes and services
↑