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The default requestFunction_ is class SRM/request The constructor for the class SRM/request calls thebase class constructor to initialize the simulator instance (ns_), the SRM agent (agent_), trace file (trace_), andthe times_ array. It then initializes its statistics_ array with the pertinent elements.A separate call to set-params{} sets the sender_, msgid_, round_ instance variables for the request object. Theobject determines C1_ and C2_ by querying its agent_. It sets its distance to the sender (times_(distance)) andfixes other scheduling parameters: the backoff constant (backoff_), the current number of backoffs (backoffCtr_),and the limit (backoffLimit_) fixed by the agent. set-params{} writes the trace entry “Q DETECT”.The final step in request{} is to schedule the timer to send the actual request at the appropriate moment. Theinstance procedure SRM/request::schedule{} uses compute-delay{} and its current backoff constant todetermine the delay. The object schedules send-request{} to be executed after delay_ seconds. The instancevariable eventID_ stores a handle to the scheduled event. The default compute-delay{} function returns avalue uniformly distributed in the interval [C 1 d s , (C 1 + C 2 )d s ], where d s is twice $times_(distance). Theschedule{} schedules an event to send a request after the computed delay. The routine writes a trace entry “QNTIMER at 〈time〉”.When the scheduled timer fires, the routine send-request{} sends the appropriate message. It invokes “$agent_ sendrequest 〈args〉” to send the request. Note that send{} is an instproc-like, executed by the command() method of the compiledobject. However, it is possible to overload the instproc-like with a specific instance procedure send{} for specific configurations.As an example, recall that the file tcl/mcast/srm-nam.tcl overloads the send{} command to set the flowidbased on type of message that is sent. send-request{} updates the statistics, and writes the trace entry “Q SENDNACK”.When the agent receives a control message for a packet for which a pending object exists, the agent will hand the message offto the object for processing.When a request for a particular packet is received, the request object can be in one of two states: it is ignoring requests,considering them to be duplicates, or it will cancel its send event and re-schedule another one, after having backed offits timer. If ignoring requests it will update its statistics, and write the trace entry “Q NACK dup”. Otherwise, set atime based on its current estimate of the delay_, until which to ignore further requests. This interval is marked bythe instance variable ignore_. If the object reschedules its timer, it will write the trace entry “ Q NACK IGNORE-BACKOFF 〈ignore〉”. Note that this re-scheduling relies on the fact that the agent has joined the multicast group, andwill therefore receive a copy of every message it sends out.When the request object receives a repair for the particular packet, it can be in one of two states: either it is still waitingfor the repair, or it has already received an earlier repair. If it is the former, there will be an event pending to send arequest, and eventID_ will point to that event. The object will compute its serviceTime, cancel that event, and set ahold-down period during which it will ignore other requests. At the end of the hold-down period, the object will ask itsagent to clear it. It will write the trace entry “Q REPAIR IGNORES 〈ignore〉”. On the other hand, if this is a duplicaterepair, the object will update its statistics, and write the trace entry “Q REPAIR dup”.When the loss recovery phase is completed by the object, Agent/SRM::clear{} will remove the object from its arrayof pending_ objects, and place it in its list of done_ objects. Periodically, the agent will cleanup and delete the done_objects.Repair Mechanisms The agent will initiate a repair if it receives a request for a packet, and it does not have a request objectpending_ for that packet. The default repair object belongs to the class SRM/repair. Barring minor differences, thesequence of events and the instance procedures in this class are identical to those for SRM/request. Rather than outline everysingle procedure, we only outline the differences from those described earlier for a request object.The repair object uses the repair parameters, D1_, D2_. A repair object does not repeatedly reschedule is timers; therefore, itdoes not use any of the backoff variables such as that used by a request object. The repair object ignores all requests for the317
same packet. The repair objet does not use the ignore_ variable that request objects use. The trace entries written by repairobjects are marginally different; they are “P NACK from 〈requester〉”, “P RTIMER at 〈fireTime〉”, “P SENDREP”, “P REPAIRIGNORES 〈holddown〉”.Apart from these differences, the calling sequence for events in a repair object is similar to that of a request object.Mechanisms for Statistics The agent, in concert with the request and repair objects, collect statistics about their responseto data loss [11]. Each call to the agent request{} procedure marks a new period. At the start of a new period,mark-period{} computes the moving average of the number of duplicates in the last period. Whenever the agent receivesa first round request from another agent, and it had sent a request in that round, then it considers the request as a duplicate request,and increments the appropriate counters. A request object does not consider duplicate requests if it did not itself send arequest in the first round. If the agent has a repair object pending, then it does not consider the arrival of duplicate requests forthat packet. The object methods SRM/request::dup-request?{} and SRM/repair::dup-request?{} encodethese policies, and return 0 or 1 as required.A request object also computes the elapsed time between when the loss is detected to when it receives the first request. Theagent computes a moving average of this elapsed time. The object computes the elapsed time (or delay) when it cancels itsscheduled event for the first round. The object invokes Agent/SRM::update-ave to compute the moving average of the delay.The agent keeps similar statistics of the duplicate repairs, and the repair delay.The agent stores the number of rounds taken for one loss recovery, to ensure that subsequent loss recovery phases for thatpacket that are not definitely not due to data loss do not account for these statistics. The agent stores the number of routestaken for a phase in the array old_. When a new loss recovery object is instantiated, the object will use the agent’s instanceprocedure round?{} to determine the number of rounds in a previous loss recovery phase for that packet.36.6 Session ObjectsSession objects, like the loss recovery objects (Section 36.5), are derived from the base class SRM Unlike the loss recoveryobjects though, the agent only creates one session object for the lifetime of the agent. The constructor invokes the baseclass constructor as before; it then sets its instance variable sessionDelay_. The agent creates the session object when itstart{}s. At that time, it also invokes SRM/session::schedule, to send a session message after sessionDelay_ seconds.When the object sends a session message, it will schedule to send the next one after some interval. It will also update itsstatistics. send-session{} writes out the trace entry “S SESSION”.The class overrides the evTrace{} routine that writes out the trace entries. SRM/session::evTrace disable writing out thetrace entry for session messages.Two types of session message scheduling strategies are currently available: The function in the base class schedules sendingsession messages at fixed intervals of sessionDelay_ jittered around a small value to avoid synchronization among all theagents at all the nodes. class SRM/session/logScaledchedules sending messages at intervals of sessionDelaytimes log 2 (groupSize_) so that the frequency of session messages is inversely proportional to the size of the group.The base class that sends messages at fixed intervals is the default sessionFunction_ for the agent.318
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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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Page 281 and 282: $ns_ rtmodel This command defines
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Page 361 and 362: Chapter 40Worm ModelIn this chapter
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41.5 Commands at a GlanceThe follow
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• HTTP response size (bytes)• s
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Chapter 42Session-level Packet Dist
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42.1.2 Inserting a Loss ModuleWhen
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Delay and Loss Modules Each receive
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Chapter 43Asim: approximate analyti
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set n(1) [$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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