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If handoff_randomization_ is true, then the next handoff interval is a random variate picked from a uniform distributionacross (0.5 ∗ term_handoff_int_, 1.5 ∗ term_handoff_int_).Crossseam ISLs are the only type of ISLs that are handed off. The criteria for handing off a crossseam ISL is whetheror not there exists a satellite in the neighboring plane that is closer to the given satellite than the one to which it is currentlyconnected. Again, a handoff timer running within the handoff manager on the polar satellite determines when the constellationis checked for handoff opportunities. Crossseam ISL handoffs are initiated by satellites in the lower-numbered plane of thetwo. It is therefore possible for a transient condition to arise in which a polar satellite has two crossseam ISLs (to differentsatellites). The satellite handoff interval is again settable from OTcl and may also be randomized:HandoffManager/Sat set sat_handoff_int_ 10; # secondsInterplane and crossseam ISLs are deactivated near the poles, because the pointing requirements for the links are too severeas the satellite draw close to one another. Shutdown of these links is governed by a parameter:HandoffManager/Sat set latitude_threshold_ 70; # degreesThe values for this parameter in the example scripts are speculative; the exact value is dependent upon the satellite hardware.The handoff manager checks the latitude of itself and its peer satellite upon a handoff timeout; if either or both of the satellitesis above latitude_threshold_ degrees latitude (north or south), the link is deactivated until both satellites drop belowthis threshold.Finally, if crossseam ISLs exist, there are certain situations in which the satellites draw too close to one another in the midlatitudes(if the orbits are not close to being pure polar orbits). We check for the occurence of this orbital overlap with thefollowing parameter:HandoffManager/Sat set longitude_threshold_ 10; # degreesAgain, the values for this parameter in the example scripts are speculative. If the two satellites are closer together in longitudethan longitude_threshold_ degrees, the link between them is deactivated. This parameter is disabled (set to 0) bydefault– all defaults for satellite-related bound variables can be found in ~ns/tcl/lib/ns-sat.tcl.17.2.4 RoutingThe current status of routing is that it is incomplete. Ideally, one should be able to run all existing ns routing protocols oversatellite links. However, many of the existing routing protocols implemented in OTcl require that the conventional ns links beused. Contributions in this area are welcome, but unfortunately it is not a trivial change.With that being said, the current routing implementation is similar to Session routing described in Chapter 29, except thatit is implemented entirely in C++. Upon each topology change, a centralized routing genie determines the global networktopology, computes new routes for all nodes, and uses the routes to build a forwarding table on each node. Currently, theslot table is kept by a routing agent on each node, and packets not destined for agents on the node are sent by default to thisrouting agent. For each destination for which the node has a route, the forwarding table contains a pointer to the head of thecorresponding outgoing link. As noted in Chapter 29, the user is cautioned that this type of centralized routing can lead tominor causality violations.The routing genie is a class SatRouteObject and is created and invoked with the following OTcl commands:set satrouteobject_ [new SatRouteObject]177
$satrouteobject_ compute_routeswhere the call to compute_routes is performed after all of the links and nodes in the simulator have been instantiated.Like the Scheduler, there is one instance of a SatRouteObject in the simulation, and it is accessed by means of an instancevariable in C++. For example, the call to recompute routes after a topology change is:SatRouteObject::instance().recompute();Despite the current use of centralized routing, the design of having a routing agent on each node was mainly done withdistributed routing in mind. Routing packets can be sent to port 255 of each node. The key to distributed routing workingcorrectly is for the routing agent to be able to determine from which link a packet arrived. This is accomplished by the inclusionof a class NetworkInterface object in each link, which uniquely labels the link on which the packet arrived. Ahelper function NsObject* intf_to_target(int label) can be used to return the head of the link correspondingto a given label. The use of routing agents parallels that of the mobility extensions, and the interested reader can turn to thoseexamples to see how to implement distributed routing protocols in this framework.The shortest-path route computations use the current propagation delay of a link as the cost metric. It is possible to computeroutes using only the hop count and not the propagation delays; in order to do so, set the following default variable to "false":SatRouteObject set metric_delay_ "true"Finally, for very large topologies (such as the Teledesic example), the centralized routing code will produce a very slowruntime because it executes an all-pairs shortest path algorithm upon each topology change even if there is no data currentlybeing sent. To speed up simulations in which there is not much data transfer but there are lots of satellites and ISLs, one candisable handoff-driven and enable data-driven route computations. With data-driven computations, routes are computed onlywhen there is a packet to send, and furthermore, a single-source shortest-path algorithm (only for the node with a packet tosend) is executed instead of an all-pairs shortest path algorithm. The following OTcl variable can configure this option (whichis set to "false" by default):SatRouteObject set data_driven_computation_ "false"17.2.5 Trace supportTracefiles using satellite nodes and links are very similar to conventional ns tracing described in Chapter 26. Special SatTraceobjects (class SatTrace derives from class Trace) are used to log the geographic latitude and longitude of the nodelogging the trace (in the case of a satellite node, the latitude and longitude correspond to the nadir point of the satellite).For example, a packet on a link from node 66 to node 26 might normally be logged as:+ 1.0000 66 26 cbr 210 ------- 0 66.0 67.0 0 0but in the satellite simulation, the position information is appended:+ 1.0000 66 26 cbr 210 ------- 0 66.0 67.0 0 0 37.90 -122.30 48.90 -120.94In this case, node 66 is at latitude 37.90 degrees, longitude -122.30 degrees, while node 26 is a LEO satellite whose subsatellitepoint is at 48.90 degrees latitude, -120.94 degrees longitude (negative latitude corresponds to south, while negative longitudecorresponds to west).178
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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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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 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: $ns add-isl $ltype $node1 $node2 $b
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Page 185 and 186: from routing agentto Node->entrySat
Page 187 and 188: $satnode add-isl This method c
Page 189 and 190: set prop [new Propagation/FreeSpace
Page 191 and 192: 18.3.2 Using shadowing modelBefore
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 $sink# mak
Page 213 and 214: Chapter 23Changes made to the IEEE
Page 215 and 216: Part IIISupport214
Page 217 and 218: endenddocument pargvcPrint out argc
Page 219 and 220: 24.4.2 Memory Conservation TipsSome
Page 221 and 222: Chapter 25Mathematical SupportThe s
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Page 225 and 226: }$sizeRNG next-substream# print the
Page 227 and 228: 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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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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