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Transcript
Interacting Network Elements: Chaos and Congestion Propagation Gábor Vattay Department of Physics of Complex Systems and Communication Networks Laboratory1 Eötvös University H-1117 Budapest, Pázmány P. s. 1/A, Hungary In mobile and ad hoc networks bandwidth is a scarce resource. Unlike in over provisioned Internet core networks, network elements in these are often used up to their limits over an extended period of time. Adaptive elastic traffic flows, such as TCP, struggle with each other for higher bandwidth share. Also, gradual dominance of peer-to-peer applications over webbing changes our assumptions on the distribution and nature of traffic sources. The role of servers and clients becomes more symmetric. Persistent massive data uploads can originate in areas of the network which were formerly designated to downlink traffic with the assumption of little or no uplink traffic. This new interacting complex network environment leads to new non-linear effects in the core, which were formerly observed in access networks only. All these new developments are going to increase the interaction of traffic flows which calls for the application of methods developed for the statistical description of interacting non-linear physical systems. In this presentation our research results in this domain are summarized. First it is demonstrated that microscopic network details can cause synchronization or chaos (Veres and Boda Infocom 2000) affecting the macroscopic behavior of the network. The detailed mechanism and description is discussed. Evidence is given supporting a description in terms of discrete chaos. Proposals will be given how to control this behavior with the methods of chaos control. Next the flow-to-flow propagation and inheritance of the statistical properties of traffic via shared congestion (Kenesi, Molnár, Veres, Vattay, SIGCOMM 2000) is discussed. It is shown that mode locking (frequency locking due to external periodic forcing), a well-known feature of certain nonlinear systems, is partially responsible for the effect. Finally new ideas on the propagation of congestion are discussed: Propagation of congestion is very common in congested highway vehicle traffic. Fukuda and Takayashu (NTT and Sony) discovered similar router-to-router congestion propagation in a sequence of highly congested routers at Keo University, Japan in 1999. We think that this phenomenon will be a general feature in the new network environments. It will be verified why such propagation occurs in TCP/IP traffic. 1 A joint laboratory of Eötvös Univesity and Ericsson Research Extended Abstract for "NeXtworking'03" First COST-IST(EU) - NSF(USA) Workshop on Exchanges & Trends in Networking, June 23-25, 2003, Chania, Crete, Greece