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F E A T U R E

Does QoS Deliver?

September 4, 2003
By Mike DeMaria

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Glossary | Weblinks

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	In this article
	Introduction
	Layer It On
	Double Pepperoni Techniques
	Traffic Shapers
	Executive Summary
	The LAN and WAN Of QoS
	Glossary \| Weblinks

QoS is full of confusing and sometimes contradictory terms. Here's how Network Computing defines them:

Quality of Service: A way to provide better or stable service for select network traffic through bandwidth or latency control.

Saturation point: The amount of load (packet count, simultaneous sessions or bandwidth utilization) that causes a network device to start dropping an unacceptable percentage of packets.

Flow: A session between two hosts (such as a TCP session). This includes handshaking, data transfer and termination. There can be multiple simultaneous flows between two hosts.

Class: A grouping of flows based on common criteria. May include protocol, source/destination address or subnet.

Classification: Detecting, identifying and potentially marking flows.

Burst rate vs. maximum rate: If a QoS device supports bursting, it can let a class or flow be configured to use more bandwidth than the maximum rate, but only if extra, unused bandwidth is available. Think of it as a second max rate: Burst will always be higher than max rate. If burst equals max rate, then bursting is effectively disabled.

Web Links

Infrastructure white papers & research reports

Infrastructure books

Definition of the DS Field

DiffServ Architecture

DiffServ white paper

IntServ & DiffServ primer

Revised ToS specification

RSVP specification

"PacketShaper 8500: Traffic Management Gets Smart"

"Fine-Tuning for QoS"