IP Telephony network engineering overview
278 Avaya Application Solutions IP Telephony Deployment Guide
In general, these concerns dictate a hierarchical network that consists of at most three layers
(
Table 65: Layers in a hierarchical network
on page 278):
●
Core
●
Distribution
●
Access
Some smaller networks can collapse the functions of several layers into one device.
For IP Telephony to work well, WAN links must be properly sized with sufficient bandwidth for
voice and data traffic. Each voice call uses between 6.3 Kbps and 80 Kbps, depending on the
desired codec, quality, and header compression used. G.729, which uses 24 Kbps of
bandwidth, is one of the most promising standards today. Traditional telephone metrics, such as
average call volume, peak volume, and average call length, can be used to size interoffice
bandwidth demands. See
Traffic engineering
for more information.
Quality of Service (QoS) also becomes increasingly important with WAN circuits. In this case,
QoS means the classification and the prioritization of voice traffic. Voice traffic must be given
absolute priority through the WAN. If links are not properly sized or queuing strategies are not
properly implemented, the quality and the timeliness of voice and data traffic will be less than
optimal.
Table 65: Layers in a hierarchical network
Layer
Description
Core
The core layer is the heart of the network. The purpose of the core
layer is to forward packets as quickly as possible. The core layer
must be designed with high availability in mind. Generally, these
high-availability features include redundant devices, redundant power
supplies, redundant processors, and redundant links. Today, core
interconnections increasingly use Gigabit Ethernet.
Distribution
The distribution layer links the access layer with the core. The
distribution layer is where QoS feature and access lists are applied.
Generally, Gigabit Ethernet connects to the core, and either Gigabit
Ethernet or 100base-TX/FX links connect the access layer.
Redundancy is important at this layer, but not as important as in the
core.
Access
The access layer connects servers and workstations. Switches at this
layer are smaller, usually 24 to 48 ports. Desktop computers and
workstations are usually connected at 10 Mbps (or 10 Mbps), and
servers are connected at 100 Mbps (or 1 Gbps). Limited redundancy
is used. Some QoS and security features can be implemented in the
access layer.
Summary of Contents for Application Solutions
Page 1: ...Avaya Application Solutions IP Telephony Deployment Guide 555 245 600 Issue 3 4 1 June 2005 ...
Page 20: ...About This Book 20 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 21: ...Issue 3 4 1 June 2005 21 Section 1 Avaya Application Solutions product guide ...
Page 22: ...22 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 106: ...Call processing 106 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 124: ...Avaya LAN switching products 124 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 139: ...Issue 3 4 1 June 2005 139 Section 2 Deploying IP Telephony ...
Page 140: ...140 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 186: ...Traffic engineering 186 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 204: ...Security 204 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 228: ...Avaya Integrated Management 228 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 274: ...Reliability and Recovery 274 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 275: ...Issue 3 4 1 June 2005 275 Section 3 Getting the IP network ready for telephony ...
Page 276: ...276 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 356: ...Network recovery 356 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 366: ...Network assessment offer 366 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 367: ...Issue 3 4 1 June 2005 367 Appendixes ...
Page 368: ...Appendixes 368 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 394: ...Access list 394 Avaya Application Solutions IP Telephony Deployment Guide ...
Page 414: ...DHCP TFTP 414 Avaya Application Solutions IP Telephony Deployment Guide ...