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entry_addrdemuxIP addressportdemuxdefaulttarget_255Src/SinkRTagentclass SatNode : public NodeSatPositionLinkHandoffMgrSatTraceList of pointers:node_head nodehead_linklist_head linklisthead_Channel* uplink_Channel* downlink_SatLinkHeadOther linkobjects...SatLinkHeadOther linkobjectsFigure 17.5: Structure of class SatNode.to populate this table correctly. The SatRouteAgent populates certain fields in the header and then sends the packet down tothe approprate link. To implement a distributed routing protocol, a new SatRouteAgent could be defined– this would learnabout topology by noting the interface index marked in each packet as it came up the stack– a helper function in the nodeintf_to_target() allows it to resolve an index value to a particular LinkHead.There are pointers to three additional objects in a SatNode. First, each SatNode contains a position object, discussed in theprevious section. Second, each SatNode contains a LinkHandoffMgr that monitors for opportunities to hand links off andcoordinates the handoffs. Satellite nodes and terminal nodes each have their specialized version of a LinkHandoffMgr.Finally, a number of pointers to objects are contained in a SatNode. We discussed linklisthead_ and nodehead_ inthe previous subsection. The uplink_ and downlink_ pointers are used for convenience under the assumption that, inmost simulations, a satellite or a terminal has only one uplink and downlink channel.17.3.3 Detailed look at satellite linksFigure 17.6 provides a more detailed look at how satellite links are composed. In this section, we describe how packetsmove up and down the stack, and the key things to note at each layer. The file ~ns/tcl/lib/ns-sat.tcl contains the various OTclinstprocs that assemble links according to Figure 17.6. We describe the composite structure herein as a “network stack.” Mostof the code for the various link components is in ~ns/satlink.{cc,h}.The entry point to a network stack is the SatLinkHead object. The SatLinkHead object derives from Class LinkHead;the aim of link head objects is to provide a uniform API for all network stacks. 4 The SatLinkHead object contains pointersto the LL, Queue, MAC, Error model, and both Phy objects. The SatLinkHead object can also be queried as to what type ofnetwork stack it is– e.g., GSL, interplane ISL, crossseam ISL, etc.. Valid codes for the type_ field are currently found in~ns/sat.h. Finally, the SatLinkHead stores a boolean variable linkup_ that indicates whether the link to at least one othernode on the channel is up. The C++ implementation of SatLinkHead is found in ~ns/satlink.{cc,h}.Packets leaving a node pass through the SatLinkHead transparently to the class SatLL object. The SatLL class derivesfrom LL (link layer). Link layer protocols (like ARQ protocols) can be defined here. The current SatLL assigns a MAC4 In the author’s opinion, all network stacks in ns should eventually have a LinkHead object at the front– the class SatLinkHead would then disappear.183
from routing agentto Node->entrySatLinkHeadNetworkInterfaceLLSat/EnqueQueueSat/RecvErrormodelSat/DropSat/DequeMacSat/ErrorPhy_txPhy_rxto SatChannelfrom SatChannelFigure 17.6: Detailed look at network interface stack.address to the packet. Note that in the satellite case, we do not use an Address Resolution Protocol (ARP); instead, we simplyuse the MAC index_ variable as its address, and we use a helper function to find the MAC address of the correspondinginterface of the next-hop node. Since class LL derives from class LinkDelay, the delay_ parameter of LinkDelaycan be used to model any processing delay in the link layer; by default this delay is zero.The next object an outgoing packet encounters is the interface queue. However, if tracing is enabled, tracing elements maysurround the queue, as shown in Figure 17.6. This part of a satellite link functions like a conventional ns link.The next layer down is the MAC layer. The MAC layer draws packets from the queue (or deque trace) object– a handshakingbetween the MAC and the queue allows the MAC to draw packets out of the queue as it needs them. The transmission timeof a packet is modelled in the MAC also– the MAC computes the transmission delay of the packet (based on the sum of theLINK_HDRSIZE field defined in satlink.h and the size field in the common packet header), and does not call up foranother packet until the current one has been “sent” to the next layer down. Therefore, it is important to set the bandwidth ofthe link correctly at this layer. For convenience, the transmit time is encoded in the mac header; this information can be usedat the receiving MAC to calculate how long it must wait to detect a collision on a packet, for example.Next, the packet is sent to a transmitting interface (Phy_tx) of class SatPhy. This object just sends the packet to the attachedchannel. We noted earlier in this chapter that all interfaces attached to a channel are part of the linked list for that channel.This is not true for transmit interfaces, however. Only receive interfaces attached to a channel comprise this linked list, sinceonly receive interfaces should get a copy of transmitted packets. The use of separate transmit and receive interfaces mirrorsthe real world where full-duplex satellite links are made up of RF channels at different frequencies.The outgoing packet is next sent to a SatChannel, which copies the packet to every receiving interface (of class SatPhy)on the channel. The Phy_rx sends the packet to the MAC layer. At the MAC layer, the packet is held for the duration of itstransmission time (and any appropriate collision detection is performed if the MAC, such as the Aloha MAC, supports it).If the packet is determined to have arrived safely at the MAC, it next passes to an ErrorModel object, if it exists. If not,the packet moves through any receive tracing objects to the SatLL object. The SatLL object passes the packet up after aprocessing delay (again, by default, the value for delay_ is zero).184
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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
Page 133 and 134: Higher LayersNode 1Node 2. . .Node
Page 135 and 136: };void recv(Packet* p, Handler*);vi
Page 137 and 138: and the frame type. It then passes
Page 139 and 140: $ll_ set delay_ $delay$ll_ set band
Page 141 and 142: 14.10 Commands at a glanceThe follo
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Page 145 and 146: Chapter 16Mobile Networking in nsTh
Page 147 and 148: entry_addrdemuxIP addressdefaulttar
Page 149 and 150: 16.1.2 Creating Node movementsThe m
Page 151 and 152: set netif $netif_($t)set mac $mac_(
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Page 157 and 158: switch(ch->ptype()) {case PT_MAC:br
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Page 163 and 164: The main problem facing the wired-c
Page 165 and 166: target_target_encapsulatorreg_agent
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Page 171 and 172: Chapter 17Satellite Networking in n
Page 173 and 174: in counter-rotating planes (where t
Page 175 and 176: • Position/Sat/Geo A geostationar
Page 177 and 178: $ns add-isl $ltype $node1 $node2 $b
Page 179 and 180: $satrouteobject_ compute_routeswher
Page 181 and 182: This will add an error model to the
Page 183: lh_firstnameobj‘‘name’’ is
Page 187 and 188: $satnode add-isl This method c
Page 189 and 190: set prop [new Propagation/FreeSpace
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Page 193 and 194: Chapter 19Energy Model in nsEnergy
Page 195 and 196: Chapter 20Directed DiffusionThe dir
Page 197 and 198: However if we have a large and dens
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Page 203 and 204: 21.2 Implementation of XCP in NSIn
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Page 207 and 208: Thruput2 0.054024 60000residue_pos_
Page 209 and 210: Chapter 22DelayBox: Per-Flow Delay
Page 211 and 212: $ns attach-agent $n_sink $sink# mak
Page 213 and 214: Chapter 23Changes made to the IEEE
Page 215 and 216: Part IIISupport214
Page 217 and 218: endenddocument pargvcPrint out argc
Page 219 and 220: 24.4.2 Memory Conservation TipsSome
Page 221 and 222: Chapter 25Mathematical SupportThe s
Page 223 and 224: set run [lindex $argv 0]}if {$run <
Page 225 and 226: }$sizeRNG next-substream# print the
Page 227 and 228: protected:RNG* rng_;};Classes deriv
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Page 231 and 232: Chapter 26Trace and Monitoring Supp
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also used to accumulate packet drop
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}name,th->size(),flags,iph->flowid(
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PT_TORA,PT_DSR,PT_AODV,// insert ne
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The QueueMonitor class is not deriv
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$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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Traffic generatorsApplication/Traff
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• recv(int nbytes)—Announces th
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1. EXPOO_Traffic—generates traffi
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set src [new Agent/UDP]set sink [ne
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Application FTP FTP objects produce
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send_data(ADU)Application(HttpApp,
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39.1.4 Transmitting user data over
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and teardown of connections. Only O
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TclObjectPagePoolPagePool/CompMathP
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PagePool/ProxyTrace takes these two
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}int id_; // object IDWebTrafSessio
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An Http/Server object waits for inc
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set tmp [new RandomVariable/Exponen
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Object Type Event Type Explaination
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Chapter 40Worm ModelIn this chapter
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$w local-p 0.5Following are some co
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(nsnode) clientcloudPackM ime(nsnod
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HTTP responsesclients servers Delay
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41.5 Commands at a GlanceThe follow
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• HTTP response size (bytes)• s
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Chapter 42Session-level Packet Dist
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42.1.2 Inserting a Loss ModuleWhen
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Delay and Loss Modules Each receive
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Chapter 43Asim: approximate analyti
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set n(1) [$ns node]set link(0:1) [$
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Part VIIIEmulation382
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When using the emulation mode, a sp
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set intf [$pf1 open readonly]puts "
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puts "install nets into taps..."$a0
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Chapter 45Nam45.1 IntroductionNam i
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• Button 6 (Chevron logo) - Close
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Second, when dealing with randomly
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dst_portaddr,seqno,flags,sname);A n
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• up• down• right• left•
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46.1.7 Agent TracingAgent trace eve
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v -t 1.0 -e node_tclscript 2 "Echo
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If nam ever gets to the end of an e
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l :link-t time-s source id-d des
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E :D :P :a :session enqueue-t time
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v :V :N :W :g :A :c :q :execute tcl
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$ns duplex-link-op orient right$ns
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Chapter 47Educational use of NS and
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Bibliography[1] C. Alaettinoğlu, A
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