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Chapter 1 Introduction 25

IP Telephony Configuration Guide

The Programming Operations Guide has a data section that describes the internet protocols and

data settings that the Business Communications Manager requires or is compatible with. Ensure

that this connection is correctly set up and working before you attempt to deploy any remote IP

devices.

LAN

A Local Area Network (LAN) is a communications network that serves users within a confined

geographical area. For Business Communications Manager 3.5, a LAN is any IP network

connected to a LAN card on the Business Communications Manager 3.5 system. Often, the LAN

can include a router that forms a connection to the Internet. A Business Communications Manager

can have up to two LAN connections.

Public Switched Telephone Network

The Public Switched Telephone Network (PSTN) can play an important role in IP telephony

communications. In many installations, the PSTN forms a fallback route. If a call across a VoIP

trunk does not have adequate voice quality, the call can be routed across the PSTN instead, either

on public lines or on a dedicated ISDN connection between the two systems. The Business

Communications Manager also serves as a gateway to the PSTN for all voice traffic on the system.

Key IP telephony concepts

In traditional telephony, the voice path between two telephones is circuit switched. This means

that the analog or digital connection between the two telephones is dedicated to the call. The voice

quality is usually excellent, since there is no other signal to interfere.

In IP telephony, each IP telephone encodes the speech at the handset microphone into small data

packets called frames. The system sends the frames across the IP network to the other telephone,

where the frames are decoded and played at the handset receiver. If some of the frames get lost

while in transit, or are delayed too long, the receiving telephone experiences poor voice quality.

On a properly-configured network, voice quality should be consistent for all IP calls.

The following sections describe some of the components that determine voice quality for IP

telephones and trunks:

• “Codecs” on page 26

• “Jitter Buffer” on page 26

• “QoS routing” on page 27

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Avaya IP Telephony Guía de configuración Pagina 25