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The ns Manual (formerly ns Notes and Documentation)1 - NM Lab at ...

The ns Manual (formerly ns Notes and Documentation)1 - NM Lab at ...

The ns Manual (formerly ns Notes and Documentation)1 - NM Lab at ...

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Chapter 43Asim: approxim<strong>at</strong>e analytical simul<strong>at</strong>ionThis chapter describes a fast approxim<strong>at</strong>e network simul<strong>at</strong>or, Asim. Asim solves the steady st<strong>at</strong>e of the network usingapproxim<strong>at</strong>e fixed points. <strong>The</strong> overall structure is shown in Figure 43.1. <strong>The</strong> user feeds a regular <strong>ns</strong> script <strong>and</strong> tur<strong>ns</strong> on theasim flag. Asim would do a fast approxim<strong>at</strong>e simul<strong>at</strong>ion of the network scenario <strong>and</strong> would present to the user the dropprobabilities of the routers, the delays <strong>and</strong> the approxim<strong>at</strong>e aggreg<strong>at</strong>e throughput of the links <strong>and</strong> the flows.In particular, we the following links/traffic are supported:• Drop Tail Queues• RED Queues• Bulk TCP flows with FTP traffic• Short lived TCP flows<strong>The</strong> d<strong>at</strong>a structures of Asim are popul<strong>at</strong>ed by a module within the Tcl space of <strong>ns</strong> from the user supplied script. Uponexecuting Asim, the results can be accessed using Tcl routines. To use the Asim within a script the user has to useSimul<strong>at</strong>or set useasim_ 1Flow st<strong>at</strong>ecomput<strong>at</strong>io<strong>ns</strong>NSscriptParserInitialconditio<strong>ns</strong>Terminalconditio<strong>ns</strong> ? Yes Networkst<strong>at</strong>eNoRouter st<strong>at</strong>ecomput<strong>at</strong>io<strong>ns</strong>Figure 43.1: <strong>The</strong> structure of Asim378

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