3Com 10014299 manual QOS Overview, Three Types of QoS Services

47 QOS OVERVIEW

This chapter covers the following topics:

■What Is QoS?

■Three Types of QoS Services

■Benefits of QoS for the Network Service

What Is QoS?

In the traditional IP network, all the packets are treated identically. Each router has to handle these packets a following first in first out (FIFO) policy. That is, it makes best effort to transmit the packets to the destination without considering the throughput, delay, jitter, drop rate of the packets, etc. This may be advantageous or disadvantageous, depending on the conditions of the network. With the rapid development of the computer networks, the voice, image, and important data that are sensitive to the bandwidth, delay and jitter are simultaneously transmitted over the network, which enrich the network resources. However, at the same time, there are more strict requirements for the network transmission data quality. They expect that a certain service guarantee in terms of the throughput, delay, delayed jitter, and packet loss ratio of the packets can be obtained, and that different services may be provided on the basis of the client types. One way to solve these problems is to increase the bandwidth of the network, however, the increase in bandwidth is so limited and so expensive that it only relieves this problem to some extent. The provision of QoS is the basic requirements for future IP networks.

Quality of Service (QoS) refers to a series of technology integrations to obtain the expected service level with respect to the throughput, delayed jitter, delay, and packet loss ratio for users. In short, QoS is the network service that provides different service qualities that meet various kinds of demands.

Three Types of QoS Services

Generally, the services of QoS are usually divided into the following three types:

■Best-effort service: This is the default service model provided by IP. It uses a FIFO (first in, first out) queue, offers the most primitive service of "routing-forwarding", and provides no guarantee for delay and reliability. It can satisfy most early networks' requirement (e.g., FTP, E-mail), but cannot provide high quality services for the developing voice and multimedia services.

■Integrated service: This model is usually applied on the edge routers. In this model, before sending a packet, it is necessary to apply for network resource and service quality through signal. After the confirmation of Resource Reservation Protocol (RSVP), the packets can be sent, and the size of the traffic is not larger than the preset traffic parameters.