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Chapter 44EmulationThis chapter describes the emulation facility of ns. Emulation refers to the ability to introduce the simulator into a livenetwork. Special objects within the simulator are capable of introducing live traffic into the simulator and injecting trafficfrom the simulator into the live network.Emulator caveats:• While the interfaces described below are not expected to change drastically, this facility is still under development andshould be considered experimental and subject to change.• The facility described here has been developed under FreeBSD 2.2.5, and use on other systems has not been tested bythe author.• Because of the currently limited portability of emulation, it is only compiled into nse (build it with “make nse”), notstandard ns.44.1 IntroductionThe emulation facility can be subdivided into two modes:1. opaque mode – live data treated as opaque data packets2. protocol mode – live data may be interpreted/generated by simulatorIn opaque mode, the simulator treats network data as uninterpreted packets. In particular, real-world protocol fields are notdirectly manipulated by the simulator. In opaque mode, live data packets may be dropped, delayed, re-ordered, or duplicated,but because no protocol processing is performed, protocol-specific traffic manipulation scenarios (e.g. “drop the TCP segmentcontaining a retransmission of sequence number 23045”) may not be performed. In protocol mode, the simulator is able tointerpret and/or generate live network traffic containing arbitrary field assignments. To date (Mar 1998), only Opaque Modeis currently implemented.The interface between the simulator and live network is provided by a collection of objects including tap agents and networkobjects. Tap agents embed live network data into simulated packets and vice-versa. Network objects are installed in tap agentsand provide an entrypoint for the sending and receipt of live data. Both objects are described in the following sections.383
When using the emulation mode, a special version of the system scheduler is used: the RealTime scheduler. This scheduleruses the same underlying structure as the standard calendar-queue based scheduler, but ties the execution of events to realtime.It is described below.44.2 Real-Time SchedulerThe real-time scheduler implements a soft real-time scheduler which ties event execution within the simulator to real time.Provided sufficient CPU horsepower is available to keep up with arriving packets, the simulator virtual time should closelytrack real-time. If the simulator becomes too slow to keep up with elapsing real time, a warning is continually produced if theskew exceeds a pre-specified constant “slop factor” (currently 10ms).The main dispatch loop is found in the routine RealTimeScheduler::run(), in the file scheduler.cc. It followsessentially the following algorithm:• While simulator is not halted– get current real time (“now”)– dispatch all pending simulator events prior to now– fetch next (future) event if there is one– delay until the next simulator event is ready or a Tcl event occurs– if a tcl event occured, re-insert next event in simulator event queue and continue– otherwise, dispatch simulator event, continue– if there was no future even, check for Tcl events and continueThe real-time scheduler should always be used with the emulation facility. Failure to do so may easily result in the simulatorrunning faster than real-time. In such cases, traffic passing through the simulated network will not be delayed by the properamount of time. Enabling the real-time scheduler requires the following specification at the beginning of a simulation script:set ns [new Simulator]$ns use-scheduler RealTime44.3 Tap AgentsThe class TapAgent is a simple class derived from the base Agent class. As such, it is able to generate simulator packetscontaining arbitrarily-assigned values within the ns common header. The tap agent handles the setting of the common headerpacket size field and the type field. It uses the packet type PT_LIVE for packets injected into the simulator. Each tap agentcan have at most one associated network object, although more than one tap agent may be instantiated on a single simulatornode.Configuration Tap agents are able to send and receive packets to/from an associated Network object. Assuming a networkobject $netobj refers to a network object, a tap agent is configured using the network method:set a0 [new Agent/Tap]384
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18 Radio Propagation Models 17718.1
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30 Multicast Routing 25130.1 Multic
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38.2.5 An example . . . . . . . . .
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X Other 40347 Educational use of NS
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# so, we lied. now, we define the t
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Chapter 2Undocumented FacilitiesNs
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Part IInterface to the Interpreter1
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• if you can do what you want by
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• tcl.result(const char* s)Pass t
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By convention in ns, the class Agen
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$object set bwvar 1500kb$object set
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For a C++ variable to be traceable,
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3.5 Class TclClassThis compiled cla
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class Packet {......static int hdrl
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The actual arguments passed by the
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class TclClass (Section 3.5) define
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Chapter 4The Class SimulatorThe ove
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4.2.2 the heap schedulerThe heap sc
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4.4 Commands at a glanceSynopsis:ns
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$ns_ dumpqCommand for dumping event
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NODEPortClassifierAgentAgentAddrCla
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The Node instance variable, entry_,
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The default values for all the abov
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The classify() method is pure virtu
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};The class imposes no direct seman
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flow-specific queuing disciplines a
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5.5 Routing Module and Classifier O
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Module NameRtModule/BaseRtModule/Mc
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$node neighborsThis returns the lis
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Linkhead_enqT_queue_ deqT_ link_ tt
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6.2 ConnectorsConnectors, unlink cl
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$ns_ link-lossmodel This function
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Chapter 7Queue Management and Packe
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}}}void Queue::resume(){Packet* p =
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7.3 Different types of Queue object
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maxidle_ is the maximum amount of t
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dst_ The destination address of pac
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7.5.2 ConfigurationRunning a JoBS s
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mean_pkt_size_ Used to set the expe
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Demarker objects$q trace-file This
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The recv() method overrides the bas
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9.2 ImplementationThe procedures an
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Average sending rateTSW window leng
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The following command adds an entry
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$qCE configQ 0 1 10 20 0.10Note tha
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Chapter 10AgentsAgents represent en
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CtrMcast/EncapCtrMcast/DecapMessage
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}bind("windowOption_", &wnd_option_
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hdr_flags* nf = (hdr_flags*)npkt->a
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public:ECHO_Timer(ECHO_Agent *a) :
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10.6.4 Using the agent through OTcl
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State Variables are:dupacks_ Number
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$agent attach-tbf Attaches a token
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(void)Scheduler::instance().schedul
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* outstanding, cancel it.*/void Tcp
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Chapter 12Packet Headers and Format
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method is now obsolete; its usage i
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Packethdrsize_next_bits()points to
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the system’s memory allocator. In
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}incr hdrlen_ $incrreturn $baseFrom
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Chapter 13Error ModelThis chapter d
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SimpleLink::errormodule argsSimulat
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This is a simple example of how to
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Higher LayersNode 1Node 2. . .Node
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};void recv(Packet* p, Handler*);vi
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and the frame type. It then passes
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$ll_ set delay_ $delay$ll_ set band
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14.10 Commands at a glanceThe follo
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15.2.1 Default Hierarchical Setting
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Chapter 16Mobile Networking in nsTh
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entry_addrdemuxIP addressdefaulttar
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16.1.2 Creating Node movementsThe m
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set netif $netif_($t)set mac $mac_(
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the hardware address of a packet’
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destined to itself to the port dmux
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switch(ch->ptype()) {case PT_MAC:br
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16.1.7 Revised format for wireless
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Packet info at "Application level"
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The main problem facing the wired-c
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target_target_encapsulatorreg_agent
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why: This avoids header clashes bet
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This command is used to create a Go
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Chapter 17Satellite Networking in n
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in counter-rotating planes (where t
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• Position/Sat/Geo A geostationar
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$ns add-isl $ltype $node1 $node2 $b
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$satrouteobject_ compute_routeswher
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This will add an error model to the
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lh_firstnameobj‘‘name’’ is
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from routing agentto Node->entrySat
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$satnode add-isl This method c
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set prop [new Propagation/FreeSpace
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18.3.2 Using shadowing modelBefore
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Chapter 19Energy Model in nsEnergy
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Chapter 20Directed DiffusionThe dir
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However if we have a large and dens
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yr application in the ns context. T
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value of opt(pre-stop) is usually t
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21.2 Implementation of XCP in NSIn
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the persistent queue length in the
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Thruput2 0.054024 60000residue_pos_
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Chapter 22DelayBox: Per-Flow Delay
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$ns attach-agent $n_sink $sink# mak
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Chapter 23Changes made to the IEEE
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Part IIISupport214
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endenddocument pargvcPrint out argc
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24.4.2 Memory Conservation TipsSome
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Chapter 25Mathematical SupportThe s
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set run [lindex $argv 0]}if {$run <
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}$sizeRNG next-substream# print the
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protected:RNG* rng_;};Classes deriv
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ns-random is implemented in ~ns/mis
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Chapter 26Trace and Monitoring Supp
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The monitor-queue function is const
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also used to accumulate packet drop
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}name,th->size(),flags,iph->flowid(
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PT_TORA,PT_DSR,PT_AODV,// insert ne
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The QueueMonitor class is not deriv
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$ns_ trace-all This is the command
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Chapter 27Test Suite SupportThe ns
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... ...}$ns_ at $opt(stop).1 "$self
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Example: To enable debugging in Que
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Chapter 29Unicast RoutingThis secti
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Asymmetric Routing Asymmetric routi
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class RouteLogic This class defines
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— The procedure init-all{} is a g
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Global Actions Once the detailed ac
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This dumps next hop information in
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$ns mrtproto ST;# specify shared tr
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Dense Mode The Dense Mode protocol
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and unique label (id). Thus, “inc
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add-iif{ifid link},add-oif{link if}
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CtrMcastComp is the centralised mul
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$ns_ mrtproto This command specifi
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Chapter 31Network DynamicsThis chap
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v 0.8123 link-up 3 5v 0.8123 link-u
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The first argument is the time at w
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$ns_ rtmodel This command defines
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$ns set-address-format hierarchical
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32.4 Hierarchical Routing with Sess
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Chapter 33UDP Agents33.1 UDP Agents
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Chapter 34TCP AgentsThis section de
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set ns [new Simulator]set node1 [$n
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34.2.1 The Base TCP SinkThe base TC
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Agent/TCP/FullTcp set dupseg_fix_ t
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34.5 Tracing TCP DynamicsThe behavi
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Chapter 35SCTP AgentsThis chapter d
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Figure 35.1: Example of a Multihome
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Note: the actual value of these tra
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1.526624 1 4 sctp 1500 -------D 0 1
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$ns at 5.0 "finish"$ns run35.5.2 Mu
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Chapter 36Agent/SRMThis chapter des
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36.1.2 Other Configuration Paramete
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3.6274 n 0 m r 1 type repair servi
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3.6029 n 3 m r 2 Q NTIMER at 3.730
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36.4 Loss Detection—The Class SRM
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same packet. The repair objet does
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}hdr_asrm* seh = (hdr_asrm*) p->acc
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set grp [Node allocaddr]$srm set ds
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#set up the multicast routingDM set
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37.3 Architecture of the PLM Protoc
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We add in void PLMLossMonitor::recv
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Part VIApplication330
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Page 359 and 360: Object Type Event Type Explaination
Page 361 and 362: Chapter 40Worm ModelIn this chapter
Page 363 and 364: $w local-p 0.5Following are some co
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Page 367 and 368: HTTP responsesclients servers Delay
Page 369 and 370: 41.5 Commands at a GlanceThe follow
Page 371 and 372: • HTTP response size (bytes)• s
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Page 375 and 376: 42.1.2 Inserting a Loss ModuleWhen
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Page 379 and 380: Chapter 43Asim: approximate analyti
Page 381 and 382: set n(1) [$ns node]set link(0:1) [$
Page 383: Part VIIIEmulation382
Page 387 and 388: set intf [$pf1 open readonly]puts "
Page 389 and 390: puts "install nets into taps..."$a0
Page 391 and 392: Chapter 45Nam45.1 IntroductionNam i
Page 393 and 394: • Button 6 (Chevron logo) - Close
Page 395 and 396: Second, when dealing with randomly
Page 397 and 398: dst_portaddr,seqno,flags,sname);A n
Page 399 and 400: • up• down• right• left•
Page 401 and 402: 46.1.7 Agent TracingAgent trace eve
Page 403 and 404: v -t 1.0 -e node_tclscript 2 "Echo
Page 405 and 406: If nam ever gets to the end of an e
Page 407 and 408: l :link-t time-s source id-d des
Page 409 and 410: E :D :P :a :session enqueue-t time
Page 411 and 412: v :V :N :W :g :A :c :q :execute tcl
Page 413 and 414: $ns duplex-link-op orient right$ns
Page 415 and 416: Chapter 47Educational use of NS and
Page 417 and 418: Bibliography[1] C. Alaettinoğlu, A
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