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

2 Faculty of Engineering, Computer and Mathematical Sciences,, University of Adelaide, 2000 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.

3 Faculty of Engineering, Computer and Mathematical Sciences,, University of Adelaide, 2000 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”

4 Faculty of Engineering, Computer and Mathematical Sciences,, University of Adelaide, 2000 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 Provides a controlled environment, reproducible results, transparency to applications Video Web TCP/IP stack (kernel) Emulation hooks Network send/recv To other “host”

5 Faculty of Engineering, Computer and Mathematical Sciences,, University of Adelaide, 2000 Existing Work in TCP/IP Network Emulation Kernel based emulators –NIST Net ( ) Linux based kernel module Supports input from applications or packet traces –Dummynet ( ) Free BSD based –NS2 emulator ( No published work since Oct 98. BSD based No interpretation of packet headers. (“opaque mode” only) –Entrapid ( Supports virtual kernels (currently Free BSD)

6 Faculty of Engineering, Computer and Mathematical Sciences,, University of Adelaide, 2000 Existing Work in TCP/IP Network Emulation –Lancaster University emulator ( 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

7 Faculty of Engineering, Computer and Mathematical Sciences,, University of Adelaide, 2000 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