Error and Traffic Control for High-Speed Networks

University dissertation from Stockholm : KTH

Abstract: The Internet evolves rapidly, both in terms of the applications that use it and the networks that carry the traffic. This creates many important research tasks, both to adapt the networks that carry the traffic to work well together with the Internet protocols and to make the protocols robust to tolerate various underlying networks. A key issue is error handling, in this thesis both error correction for both underlying optical networks and integrated in the Internet protocols are studied. The results show that error control should not be considered in isolation: by combining it with traffic control we find that it is possible to implement new services in elegant ways that are well suited for deployment in the Internet.The traffic in the Internet is increasingly being carried over optical links which offer large capacity. When optical fibers are deployed in access networks, the components need to be cheap and an important factor is sharing of the fibers between several users. One technology that can help in providing these advantages is optical code division multiple access (CDMA). If low-complexity components are used, noise will be a significant problem and there is a need for error control to keep the error rates at an acceptable level. Error control for an optical CDMA network is one of the topics in this thesis. Our results show that there is a strong correlation between the error rates and the number of active users, which indicates the need for traffic control. Moreover, the performance is significantly improved by error correction and soft decoding.In wireless networks, packet loss caused by transmission errors is a well-known problem. In particular for the transmission control protocol (TCP), the performance is severely degraded by losses that are not caused by congestion. In this thesis, end-to-end forward error correction (FEC) is considered as a solution. A further advantage of end-to-end FEC is that it can also improve TCP performance for large bandwidth-delay product paths, where TCP is also known to perform badly. The results show that the error control has to be designed with the requirements of the traffic control in mind.The requirement on the network service is very different for a service like IP-telephony compared to web surfing; hence new traffic control methods are needed. For conversational applications it is important to have predictable performance during a session. For this purpose probe-based admission control can be used, but a problem with this approach is that it cannot isolate different applications with differing requirements on the loss rate. A solution is to combine the admission control with FEC to protect the ongoing sessions and provide consistent quality. Based on these ideas, a service architecture that can be deployed without upgrading the network is proposed and evaluated. The last part of this thesis also shows how this host based scheme could evolve into more complex schemes as network support is provided.