Qos Overview; Introduction To Qos; Qos Service Models; Best-Effort Service Model - H3C S5820X Series Configuration Manual

QoS overview

This chapter includes these sections:

Introduction to QoS

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QoS service models

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QoS techniques overview
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Introduction to QoS
In data communications, Quality of Service (QoS) is the ability of a network to provide differentiated
service guarantees for diversified traffic in terms of bandwidth, delay, jitter, and drop rate.
Network resources are scarce. The contention for resources requires that QoS prioritize important traffic
flows over trivial ones. For example, in the case of fixed bandwidth, if a traffic flow gets more bandwidth,
the other traffic flows will get less bandwidth and may be affected. When making a QoS scheme, you
must consider the characteristics of various applications to balance the interests of diversified users and
to utilize network resources.
The following sections describe some typical QoS service models and widely used, mature QoS
techniques. By appropriately using these techniques, you can improve QoS effectively.
QoS service models
This section covers the following typical QoS service models:
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Best-effort service model

IntServ model

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DiffServ model
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Best-effort service model
Best effort is a single-service model and also the simplest service model. In the best-effort service model,
the network does its best to deliver packets, but does not guarantee delay or reliability.
The best-effort service model is the default model in the Internet and applies to most network applications.
It uses the first in first out (FIFO) queuing mechanism.
IntServ model
The integrated service (IntServ) model is a multiple-service model that can accommodate diverse QoS
requirements. It provides the most granularly differentiated QoS by identifying and guaranteeing definite
QoS for each data flow.
In the IntServ model, an application must request service from the network before it sends data. IntServ
signals the service request with the Resource Reservation Protocol (RSVP). All nodes receiving the request
reserve resources as requested and maintain state information for the application flow.
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