1-2Traditional Packet Forwarding ServiceIn traditional IP networks, packets are treated equally. That is, the FIFO (first in first out)policy is adopted for packet processing. Network resources required for packet forwardingis determined by the order in which packets arrive. All the packets share the resources ofthe network. Network resources available to the packets completely depend on the timethey arrive. This service policy is known as Best-effort, which delivers the packets to theirdestination with the best effort, with no assurance and guarantee for delivery delay, jitter,packet loss ratio, reliability, and so on.The traditional Best-Effort service policy is only suitable for applications insensitive tobandwidth and delay, such as WWW, E-mail and FTP.New Applications and New RequirementsWith the expansion of computer network, more and more networks become part of theInternet. The Internet gains rapid development in terms of scale, coverage and userquantities. More and more users use the Internet as a platform for their services and fordata transmission.Besides the traditional applications such as WWW, E-mail, and FTP, new services aredeveloped on the Internet, such as tele-education, telemedicine, video telephone,videoconference and Video-on-Demand (VoD). Enterprise users expect to connect theirregional branches together using VPN techniques for coping with daily business, forinstance, accessing databases or manage remote equipments through Telnet.All these new applications have one thing in common, that is, they have specialrequirements for bandwidth, delay, and jitter. For instance, bandwidth, delay, and jitter arecritical for videoconference and VoD. As for other applications, such as transactionprocessing and Telnet, although bandwidth is not as critical, a too long delay may causeunexpected results. That is, they need to get serviced in time even if congestion occurs.Newly emerging applications demand higher service performance from IP networks. Inaddition to simply delivering packets to their destinations, better network services aredemanded, such as allocating dedicated bandwidth, reducing packet loss ratio, avoidingcongestion, regulating network traffic, and setting priority of the packets. To meet thoserequirements, the network should be provided with better service capability.
