Overview; Evaluating Traffic On Your Network - HP 7102dl - ProCurve Secure Router Configuration Manual

Setting Up Quality of Service

Overview

8-4
Overview
Quality of service (QoS) protocols allow a router to distinguish different
classes of traffic and serve each class according to its priority and needs.

Evaluating Traffic on Your Network

Several factors define the QoS that traffic receives, including:
bandwidth
delay
number of dropped packets
Clearly, high bandwidth is better than low bandwidth, and low delay and low
numbers of dropped packets are better than long delay and high numbers of
dropped packets.
However, sometimes you must balance these factors. A link may have low
bandwidth, but also low delay. You should understand which factors are most
important for managing QoS for different kinds of traffic.
A router must handle several kinds of traffic, including:
Data—Data packets tend to be relatively large. They can be fragmented
and reconstructed without damage to their integrity. Data traffic can
tolerate high latency and is bursty: packets can be queued and sent at
various speeds without excessively degrading QoS. For data, bandwidth
is usually more important than delay in determining the QoS. For example,
more bandwidth helps FTP applications download files more quickly.
However, less delay at any given moment does not perceptibly increase
the QoS because the entire file must be downloaded before it can be used.
Real-time traffic—Real-time traffic requires low latency; it cannot tolerate
delays. Real-time traffic includes Voice over IP (VoIP) and interactive
traffic such as Telnet. Such packets are typically small, and they cannot
be fragmented. As well as requiring low latency, voice and other real-time
traffic must have low jitter: that is, the delay for each packet transmitted
should be similar so that the receiver does not hear a difference in
conversation.
High-priority traffic—Mission-critical traffic should be guaranteed a cer-
tain amount of bandwidth and should not be dropped when congestion
occurs.