NS internals

	Velibor Markovski
	Communication Networks Laboratory
	School of Engineering Science
	Simon Fraser University

Software architecture

	Split programming model (C++ and OTcl)
	Simulation kernel ® C++
	Simulation definition, configuration and control ® OTcl
	Tradeoff: performance vs. flexibility

Class mirroring

	OTcl class hierarchy
	C++ class hierarchy

Simple script

	Two nodes
	CBR traffic from source to destination
	UDP used as transport protocol

Simple script

Simple script - initialization

Simple script - initialization

Simple script - initialization

Simple script - initialization

Simple script - initialization

Simple script - initialization

Simple script – node creation

Simple script – link creation

Simple script – setting up source

Simple script – setting up sink

Simple script – connecting nodes

Simple script – schedule “at” events

Event scheduler

Initial events

Initial and follow-up events

Initial and follow-up events

Scheduler’s main functions

	Schedule events at certain time
		Insert events in the list
	Deque events from the list
	Dispatch dequed events
		Call appropriate event handler

Back to our example

Back to our example

Back to our example

Back to our example

Even more details…

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Complex software structure

	Approximate numbers:
	27K lines of C++ code (ns-2.1b5)
	12K lines of OTcl code
	18K lines of test suites and examples

Why simulators at all?

	Inexpensive
	Flexible:
		with scenario generation
		with link speeds
		with topologies
	Access to ALL data

Alternatives to simulation

	Testbeds
	Emulation (testbed-simulator mix)
	Live Internet tests

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