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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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Higher LayersNode 1Node 2. . .Node NLink LayerQueueQueue. . .QueueLLLLLLMac LayerMacMac. . .MacPhysical LayerChannelClassifier/Mac14.2 Components of a LANFigure 14.1: Connectivity within a LANLanLink captures the functionality of the three lowest layers in the network stack:1. Link Layer (LL)2. Medium Access Control (MAC) Layer3. Physical (PHY) LayerFigure 14.1 illustr<strong>at</strong>es the extended network stack th<strong>at</strong> makes simul<strong>at</strong>io<strong>ns</strong> of local area network possible in <strong>ns</strong>. A packet sentdown the stack flows through the link layer (Queue <strong>and</strong> LL), the MAC layer (Mac), <strong>and</strong> the physical layer (Channel toClassifier/Mac). <strong>The</strong> packet then makes its way up the stack through the Mac, <strong>and</strong> the LL.At the bottom of the stack, the physical layer is composed of two simul<strong>at</strong>ion objects: the Channel <strong>and</strong> Classifier/Mac.<strong>The</strong> Channel object simul<strong>at</strong>es the shared medium <strong>and</strong> supports the medium access mechanisms of the MAC objects on thesending side of the tra<strong>ns</strong>mission. On the receiving side, the Classifier/Mac is respo<strong>ns</strong>ible for delivering <strong>and</strong> optionallyreplic<strong>at</strong>ing packets to the receiving MAC objects.Depending on the type of physical layer, the MAC layer must contain a certain set of functionalities such as: carrier se<strong>ns</strong>e,collision detection, collision avoidance, etc. Since these functionalities affect both the sending <strong>and</strong> receiving sides, they are132

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