Track your QoS SLA
Tom Lancaster

There are many variables of performance that will make your VoIP solution better or worse, all under the umbrella of QoS. Tracking your SLA will give you an idea of where your performance needs to improve.

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QoS isn't an all-or-nothing technology. There are many different aspects that contribute to the "quality of service" and each of these aspects is measured independently. They are also not binary. In other words, they could be many different values instead of just "yes or no" or "on or off." So in the real world, your network is likely to excel in some of these areas and it could probably use some work in others. Thus, it is important to measure and track these values that combine to affect your users' experience.

In networks where the service-provider/customer relationship is well defined, this measurement and tracking are often accomplished as a part of a Service Level Agreement, or SLA. But even if you're not subject to one of these agreements now, it can be a good exercise to help you improve your network.

The meat of an SLA typically looks something like this:

Service Metrics	Service Level
------------------		----------------
Net Availability	99.9%
Mean Time 		1500 hrs
Between Failures
LAN Latency		<20 ms average (mean)
WAN Latency		<80 ms average (mean)
Packet Loss		<0.5% average (mean)

This information can be invaluable. For instance, if you want to sell an IP Telephony solution to your management, it will be much easier for you if you can show your network has exceeded its SLA for several months. This can give management the confidence they need that the network is ready to support critical voice traffic.

In preparation for VoIP, you can also show that you plan to update the SLA with VoIP-specific metrics, such as jitter, dropped calls, and RSVP admissions and rejections.


Thomas Alexander Lancaster IV is a consultant and author with over ten years experience in the networking industry, focused on Internet infrastructure.

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Related Book

Internet Performance Survival Guide: QoS Strategies for Multi-Service Networks
by Geoff Huston
Online Price: $42.49
Publisher Name: John Wiley & Sons
Date published: February 2000
Summary:
The bestselling author of the ISP Survival Guide returns with an unprecedented look at network performance solutions delivered from an Internet perspective. With their signature knack for pinpointing highly detailed specifics in the midst of a comprehensive, straightforward overview of every possible snag and solution, authors Geoff Huston and Paul Ferguson cover the latest in standards work, the advantages and disadvantages of specific performance-tuning tools, design guidelines for achieving performance thresholds, fascinating performance-management predictions for the new century, and much more.


This was first published in September 2001

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