Traffic Control for VBR Video in Packet Switched Networks

Sammanfattning: The best effort service offered by the Internet is notsatisfactory for the transmission of loss and delay sensitivedata, such as real-time voice and video. In order to provideservice guarantees at reasonably high load levels, additionalcontrol functions haveto be employed in the network. Theintroduction of these functions is a critical issue, as severalaspects have to be taken into account, like scalability,economic feasibility and compliance with the end-to-endargument, one of the basic principles underlying the currentInternet architecture. To fulfill these requirements controlfunctions should be put at the network edge, while the core ofthe network should be kept simple to maintain the flexibilityof the network. The endpoint measurement-based admission control schemesproposed recently follow this principle. Most of theseadmission control schemes, however, suffer from limitedgranularity, namely, the QoS guarantees (packet loss, delay anddelay jitter) within a service class are the same for allstreams. Quality differentiation thus either requires qualityspecific service classes, which is in contradiction to theend-to-end argument, or the use of additional traffic controlfunctions at the network edge. Such additional control functions can decrease the packetloss probability given by the admission control to a levelrequired by the application by introducing additional delay.Delay limited shaping can be used to decrease the burstiness ofthe streams and thus their packet loss probability at the priceof increased delay. Forward error correction can be used torecover from losses within the network while incurringincreased delay and some overhead. This thesis gives an evaluation of how the different controlfunctions can work together to improve transmission quality,and thus the perceived visual quality. The effects of the jointuse of the control functions shaping and forward errorcorrection are evaluated, and the optimal allocation of thedelay is investigated. An exact mathematical model of thepacket loss process for multimedia traffic is presented, andits applicability is evaluated.