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Issue 6 January 2008 283
IP Telephony network engineering overview
In the early days of local area networking, network designers used hubs to attach servers and
workstations, and routers to segment the network into manageable pieces. Because of the high
cost of router interfaces and the inherent limitations of shared-media hubs, network design was
generally well done. In recent years, with the rise of switches to segment networks, designers
were able to hide certain faults in their networks and still get good performance. As a result,
network design was often less than optimal. IP Telephony places new demands on the network.
Suboptimal design cannot cope with these demands. Even with switches installed, a company
must follow industry best practices to have a properly functioning voice network. Because most
users do not tolerate poor voice quality, administrators should implement a well-designed
network before they begin IP Telephony pilot programs or deployments.
This section contains network design recommendations in the following topics:
● Overview
● Voice quality
● Best practices
● Common issues
Overview
Industry best practices dictate that a network be designed with consideration of the following
factors:
● Reliability and redundancy
● Scalability
● Manageability
● Bandwidth
Voice mandates consideration of the following additional factors when designing a network:
● Delay
● Jitter
● Loss
● Duplex