1-11 QoS ConfigurationOverviewIntroduction to QoSQuality of Service (QoS) is a concept concerning service demand and supply. It reflects the ability tomeet customer needs. Generally, QoS does not focus on grading services precisely, but on improvingservices under certain conditions.In an internet, QoS refers to the ability of the network to forward packets. The evaluation on QoS of anetwork can be based on different aspects because the network may provide various services.Generally, QoS refers to the ability to provide improved service by addressing the essential issues suchas delay, jitter, and packet loss ratio in the packet forwarding process.Traditional Packet Forwarding ServiceIn traditional IP networks, packets are treated equally. That is, the FIFO (first in first out) policy isadopted for packet processing. Network resources required for packet forwarding is determined by theorder in which packets arrive. All the packets share the resources of the network. Network resourcesavailable to the packets completely depend on the time they arrive. This service policy is known asBest-effort, which delivers the packets to their destination with the best effort, with no assurance andguarantee for delivery delay, jitter, packet loss ratio, reliability, and so on.The traditional Best-Effort service policy is only suitable for applications insensitive to bandwidth anddelay, such as WWW, file transfer and E-mail.New Applications and New RequirementsWith the expansion of computer network, more and more networks become part of the Internet. TheInternet gains rapid development in terms of scale, coverage and user quantities. More and more usersuse the Internet as a platform for their services and for data transmission.Besides the traditional applications such as WWW, E-mail, and FTP, new services are developed on theInternet, such as tele-education, telemedicine, video telephone, videoconference andVideo-on-Demand (VoD). Enterprise users expect to connect their regional branches together usingVPN techniques for coping with daily business, for instance, accessing databases or manage remoteequipments through Telnet.All these new applications have one thing in common, that is, they have special requirements forbandwidth, delay, and jitter. For instance, bandwidth, delay, and jitter are critical for videoconferenceand VoD. As for other applications, such as transaction processing and Telnet, although bandwidth isnot as critical, a too long delay may cause unexpected results. That is, they need to get serviced in timeeven if congestion occurs.Newly emerging applications demand higher service performance from IP networks. In addition tosimply delivering packets to their destinations, better network services are demanded, such asallocating dedicated bandwidth, reducing packet loss ratio, avoiding congestion, regulating network
