H3C S5500-SI Series Operation Manual

Also see for S5500-SI Series: Configuration Operation manual Configuration guide Configuration guide Configuration guide

Operation Manual – QoSH3C S5500-SI Series Ethernet Switches Chapter 1 QoS Overview1-1Chapter 1 QoS Overview1.1 IntroductionQuality of Service (QoS) is a concept generally existing in occasions where servicesupply-demand relations exist. QoS measures the ability to meet the service needs ofcustomers. Generally, the evaluation is not to give precise grading. The purpose of theevaluation is to analyze the conditions where the services are good and the conditionswhere the services still need to be improved, so that specific improvements can beimplemented.In Internet, QoS measures the ability of the network to deliver packets. The evaluationon QoS can be based on different aspects because the network provides diversifiedservices. Generally speaking, QoS is the evaluation on the service ability to support thecritical indexes such as delay, delay jitter and packet loss rate in packet delivery.1.2 Traditional Packet Delivery ServiceThe traditional IP network treats all the packets equally. The switch adopts the first infirst out (FIFO) policy in packet processing and assigns resources necessary for packetforwarding according to the arrival time of the packet. All the packets share the networkand router resources. The resources that the packet can get depend completely on thechance at packets arrival.This service policy is called Best-Effort. The switch makes its best effort to deliver thepackets to the destination but it cannot provide any guarantee for delay, delay jitter,packet loss rate, and reliability in packet delivery.The traditional Best-Effort service policy is only applicable to services such as WWW,FTP, and E-mail, which are not sensitive to the bandwidth and the delay performance.1.3 New Requirements Brought forth by New ServicesWith the fast development of computer networks, more and more networks areconnected into Internet. Internet extends very quickly in scale, coverage and thenumber of users. More and more users use the Internet as a platform for datatransmission and develop various applications on it.Besides traditional applications such as WWW, FTP, and E-mail, Internet users also tryto develop new services on Internet, such as tele-education, tele-medicine, videophones, video conferencing, and video on demand (VOD). Enterprise users also hopeto connect their branch offices in different locations through the VPN technology todevelop some transaction applications, such as to access to the database of thecompany or to manage remote switches through Telnet.

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