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Network Emulation for the Study and Validation of Traffic Models, Congestion and Flow Control in TCP/IP Networks Cheryl Pope Lecturer Department of Computer Science Faculty of Engineering, Computer and Mathematical Sciences The University of Adelaide Validating Networks • Motivations for evaluation environments – adaptive applications (multimedia, streaming, mobile) – validation of traffic models (traffic aggregation) – protocol testing (TCP congestion/flow control) – QoS support (flows, IntServe/DiffServe behaviours) – distributed applications • Current evaluation environments – simulation (most common) • Software based model of the underlying network. – “live” testing (less common) • Dedicated network resource or testing on the network to be used. – emulation (even less common) • Simulation which interacts with the network protocol stacks. Faculty of Engineering, Computer and Mathematical Sciences,, University of Adelaide, 2000 2 Evaluation environments • Simulation – + high level of control – + repeatable experiments – - difficult to accurately capture all aspects of the network • traffic models may be incorrect (Paxson-Floyd 95) • interaction of protocols • accuracy of protocol implementation • Live Testing – + very accurate model of the network – + no conversion of simulated applications needed – - low level of control (more difficult to create reproducible results) – - difficult to introduce new protocol behaviour other than end-to-end – - often just a “wire” Faculty of Engineering, Computer and Mathematical Sciences,, University of Adelaide, 2000 3 Network Emulation • Network emulation aims to combine the best properties of both simulation and “live” testing • Network functions are intercepted and delays, loss, etc. simulated – kernel network stack – socket API Video Web Network send/recv Emulation hooks TCP/IP stack (kernel) To other “host” • Provides a controlled environment, reproducible results, transparency to applications Faculty of Engineering, Computer and Mathematical Sciences,, University of Adelaide, 2000 4 Existing Work in TCP/IP Network Emulation • Kernel based emulators – NIST Net (www.antd.nist.gov/itg/nistnet/ ) • Linux based kernel module • Supports input from applications or packet traces – Dummynet (www.iet.unipi.it/~luigi/ip_dummynet/ ) • Free BSD based – NS2 emulator (www.isi.edu/nsnam/ns/ns-emulation.html) • No published work since Oct 98. • BSD based • No interpretation of packet headers. (“opaque mode” only) – Entrapid (www.cs.cornell.edu/skeshav/papers/simphony.ps) • Supports virtual kernels (currently Free BSD) Faculty of Engineering, Computer and Mathematical Sciences,, University of Adelaide, 2000 5 Existing Work in TCP/IP Network Emulation – Lancaster University emulator (www.comps.lancs.ac.uk/computing/research/mpg/reports_1995.html) • Aimed at emulation of mobile networks with high delay • Central emulation process (<16 nodes) • Unix (Sun) • Non-kernel based – Delay Line - University of Newcastle (ajuna.ncl.ac.uk/group/papers/p040.ps) • interception of socket calls • must recompile applications to use emulator Faculty of Engineering, Computer and Mathematical Sciences,, University of Adelaide, 2000 6 Goals of the Emulation Environment • Both IPv6 and IPv4 support – IPv6 flows for QoS behaviours – RSVP – backwards compatability for IPv4 applications and existing network traffic traces – multicasting support • No expertise beyond that required by simulators – No “kernel hacking” for users – simple insertion of user defined behaviours without recompilation of main OS kernel – dynamic reconfiguration – visualisation of emulation • Scalability – allow for interconnectivity between emulators to build larger emulations Faculty of Engineering, Computer and Mathematical Sciences,, University of Adelaide, 2000 7