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Network design
304 Avaya Application Solutions IP Telephony Deployment Guide
Converged network design
Converged networks require the application of good management and control practices to
support and sustain the deployment of IP telephony. The first step in implementing an IP
telephony system is making the commitment to provide a network capable of supporting a real
time application such as voice. With many large enterprise networks averaging over 500 hours
of downtime per year in 2003 [1], this level of commitment seems to be the exception rather
than the rule.
Design and Management
Highly available networks do not just happen. They must be planned and maintained. The
probability of success for both of those activities is improved by the application of three
fundamental principles -- Simplicity, Manageability and Scalability.
According to an article published in Network World [2] 59% of network downtime was
attributable to routing management with approximately 36% of that caused by configuration
errors. In another instance a report published by Infonetics Research and reviewed in
DMReview [3] attributed the single largest portion (32%) of downtime costs to Application
problems with software failure (36%) and human error (22%) precipitating those outages over
half of the time. In another article available through Infonetics Research [4] the author cites
human error as “the most troubling” cause of outages due to the time and cost of correcting the
problems. Older studies [5] attribute as much as 80% of all mission-critical application service
downtime to “people or process” failures.
It is clear from the available data that in order to deploy a business-critical IP based service the
network upon which it runs must be:
● Easy to configure.
● Easy to monitor and troubleshoot.
● Extensible with minimum reconfiguration. That is, designed with enough resources to grow
with the business it supports.
Design for Simplicity
It is self evident that action without understanding is unpredictable. IT staff must interact with the
network, so if the system is difficult to understand the probability of error increases. With this
thought in mind it is advisable to reduce the number protocols and services on any network
segment and reduce the number of decisions the network must make. Simple, documentable,
reproducible and verifiable configurations are a must for IP telephony deployment. The IT staff
responsible for the network needs to understand how it works, and new staff should be easy to