Emergency calling solutions exist to retrieve user's information and geolocation for both E.164 and PLMN telephone networks:

• An E.164 emergency call relies on the public phone directory to retrieve information;

• A PLMN emergency call relies on Cell Ids and radio triangulation process to retrieve information.

This TSB covers issues associated with support of ECS from IP Telephony terminals connected to an Enterprise Network (EN). It describes new network architecture elements needed to support ECS, and the functionality of those new elements, in North America. Many countries have similar ECS requirements. Portions of this document may be applicable in providing guidance in solutions for those requirements.

This TSB addresses ECS calls placed from fixed, mobile, remote dial-in, or wireless access VoIP terminals, as shown in Figure 1. This figure also illustrates similar access scenarios for ECS calls placed directly through an ISP. Solutions contained within this TSB may apply to the non-enterprise environment as well. This TSB does not address scenarios for devices connected to VoIP networks through gateways.

Use cases:

• (A) EN may be directly accessed by the user's terminal, without crossing a tier's network.

• (B) EN may also be accessed through one (or several) tier's network(s):

o (B.1) Case of multi-site enterprises, using leased-links to connect distant sites;

o (B.2) Case of public access point based connection, using VPN

o (B.3) Case of private (residential) access point based solution, also using VPN.

• (C) EN may finally be accessed by a "guest" terminal, that doesn't belong to the enterprise fleet, but that anyway tries to setup an emergency call.

Cases (A) and (B.1) are covered by immediate solutions, while cases (B.2), (B.3) and (C) are mentioned for further study, some material being proposed in the document annexes.

Many ECS support issues will require further investigation, and are beyond the scope of this document. These include for example:

• Dialing procedures

• Call Reliability

• Call set-up delay Call queuing

• Calling feature override (e.g. call forwarding, call waiting, call conferencing, caller ID suppression, call priority interruption [18] and do not disturb.)

• Access by persons with disabilities (e.g. TDD devices)

• Language-based call routing

• Use of a Private Safety Answering Point

• Transmission of supplementary call data (e.g. biometrics)

Please note that using managed, switched infrastructure described in this TSB does not necessarily provide a solution for the problem of remote access via VPN connectivity It also assumes that a sufficient number of local tandem ECS trunk connections exist to allow for routing to the appropriate PSAP.