Avaya BCM Emergency Services Access (ESA) User Manual download pdf (Page 7)

Technical Solution Guide for BCM ESA v2.2 November 2006

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6 Nortel Confidential

1. Introduction

Emergency Services Access (ESA), through its North American “dial 911” instantiation, has become integrated

into the fabric of the telecommunications network. Supporting this lifeline service is an infrastructure of Public

Safety Answering Point (PSAP) which can respond to multiple emergency service requests.

Once a subscriber dials the requisite access code, such as 911, the hosting telecom network executes a simple

routing process based upon the origination Directory Number (DN) which results in the call arriving at a

geographically relevant PSAP. Known by many names Calling Line ID (CLID), or in BCM speak the Outgoing Line

Identification (OLI), it is this originating DN that is the key to effective ESA.

1.1 Background

Given the importance of the CLID or OLI to ESA, this section will review the fundamentals involved.

For Voice based services, BCMs connect to the PSTN in the following manner:

• Individual telephone lines, also called analogue trunks

• Time Division Multiplexed (TDM) facilities composed of multiple lines, also called digital trunks

• Through an Internet Protocol (IP) connection for Voice over IP (VoIP), this is commonly called IP Trunking

1.1.1 Analogue Trunks

In addition to the voice component of a call, a telephone line passes a limited quantity of telephony information to

and from the Central Office (CO). The signaling used to indicate that a call is incoming, is electrical in nature and

involves monitoring the polarity and level of the line’s voltage.

In essence, this method will only allow the subscriber communicate the digits dialed; it is the CO that stores and

applies the line’s CLID to outgoing call. This CLID is then used by the PSAP to look-up the address of the caller.

Each analogue trunk has an individual Listed Directory Number (LDN).

1.1.2 Digital Trunks

This technology was a major step forward in the advanced of telecommunications systems, in that up to 24

individual voice conversations can be digitized and transported on a single facility. And with the advent of trunking

protocols such as ISDN Primary Rate Interface (PRI), additional services and features are supported over the

trunk.

Digital trunks have one or more LDNs associated to the TDM timeslots it carries. In the case of multiple LDNs, the

Telco and ESA Authority work in conjunction with the customer to ensure that the correct street address is

recorded in the Automatic Line Identification (ALI) database.

In the case of a basic, non-PRI digital trunk, it operates as simple grouping of 24 individual lines. The call

signaling is accomplished via multiple schemas which are variants of the method used for individual lines. Known

by names such as E&M and Per Trunk Signaling (PTS), these methods continue to rely upon the CO to correctly

add the CLID defined for individual timeslot on the trunk for ESA.

For PRI trunks, electrical call signaling methods have been replaced by a protocol where a SETUP message is

sent to the CO when a call is originated. This messaging based system, in conjunction with the dedication of one

timeslot for signaling, permit an expansion of the information that can be exchanged. This translates into the

ability of the originator to pass on their CLID to the CO.

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Avaya BCM Emergency Services Access (ESA) User Manual Page 7