Branch Office Scenario

In most cases, the country regulations force that the A-number sent to the public exchange is within the direct-in-dialling number series handled in that PSTN area.

In complex network configurations with remote branch offices in different geographical areas, when the emergency call is set up through the public trunk located in the main office, the remote branch offices must provide A-numbers associated to their remote geographical area, see Figure 1.

Furthermore, the emergency calls made from the remote branch office must be set up to the local emergency centers.

Figure 1. Example of a complex network configuration with Remote Branch Offices

The correct setup of the emergency calls to the local emergency center and the provision of the correct user location to the center are achieved by means of the configurations below.

When MX-ONE IP telephones are used in H.323 mode, there is functionality for registration towards the branch node when the connection with the main site is faulty. When the connection towards the main site is up again, the telephones will register towards the main site.

Emergency Calls from Remote Logged-Off IP Telephones (Using H.323)

The local presence at the remote branch office can be achieved by using either a Survivable Branch Node (SBN) or an MX-ONE. In all the figures and examples in this document, the SBN is used.

The emergency calls are set up directly to the SBN and not to the main office. These calls are established to the local emergency center and the telephone configuration file must be initiated according to these premises.

The A-number is initiated by the system administrator, in the telephone configuration file, according to the geographical location of the remote branch office.

The A-number can be a local extension, operator group, hunt group, or a ring group initiated in the SBN.

Figure 2. Emergency Call from a Remote Logged-Off IP Telephone

Emergency Calls from Remote Logged-On IP Telephones

The local presence at the remote branch office can be achieved by using either an SBN or an MX-ONE. The SBN is used in all figures and examples in this document.

The IP telephones of a remote branch office must belong to the same domain. The following data must be initiated for the remote branch office domain:

The A-number and the type of number, in such way that the A-number is prefixed by the main office according to the geographical location of the remote branch office. It is possible that the system administrator prefers to prefix the A-number manually and avoid the prefixing done by the system. In this case, the A-number must be initiated with all necessary prefixes, and the type of number must be initiated to avoid the system prefixing.
The area code for the user geographical location.

The logged-on IP telephones are registered in the main office gatekeeper; therefore, the calls made by these telephones are initiated from the main office. When remote branch offices exist, the main office normally distributes the public calls from remote IP telephones to the PSTN through the remote branch office SBN.

The domain area code of the remote branch offices is used to distribute the emergency calls from remote IP telephones to the remote branch office SBN. In this way the emergency calls are set up to the local emergency center. For the main office to distribute these calls to the proper SBN, LCR tables must be initiated.

Figure 3. Emergency Call from a Remote Logged-On IP Telephone

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