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eceived from multicast group that must be processed. Therefore, the application agent must set the packet’s destinationaddress to zero.For locally originated data, the agent adds the appropriate SRM headers, sets the destination address to the multicast group,and forwards the packet to its target.On receiving a data message from the group, recv_data(sender, msgid) will update its state marking message 〈sender,msgid〉 received, and possibly trigger requests if it detects losses. In addition, if the message was an older message receivedout of order, then there must be a pending request or repair that must be cleared. In that case, the compiled object invokes theOTcl instance procedure, recv-data{sender, msgid} 2 .Currently, there is no provision for the receivers to actually receive any application data. The agent does not also store any ofthe user data. It only generates repair messages of the appropriate size, defined by the instance variable packetSize_. However,the agent assumes that any application data is placed in the data portion of the packet, pointed to by packet->accessdata().Request Packets On receiving a request, recv_rqst(sender, msgid) will check whether it needs to schedule requests forother missing data. If it has received this request before it was aware that the source had generated this data message (i.e.,the sequence number of the request is higher than the last known sequence number of data from this source), then the agentcan infer that it is missing this, as well as data from the last known sequence number onwards; it schedules requests for all ofthe missing data and returns. On the other hand, if the sequence number of the request is less than the last known sequencenumber from the source, then the agent can be in one of three states: (1) it does not have this data, and has a request pendingfor it, (2) it has the data, and has seen an earlier request, upon which it has a repair pending for it, or (3) it has the data, andit should instantiate a repair. All of these error recovery mechanisms are done in OTcl; recv_rqst() invokes the instanceprocedure recv-rqst{sender, msgid, requester} for further processing.Repair Packets On receiving a repair, recv_repr(sender, msgid) will check whether it needs to schedule requests forother missing data. If it has received this repair before it was aware that the source had generated this data message (i.e., thesequence number of the repair is higher than the last known sequence number of data from this source), then the agent caninfer that it is missing all data between the last known sequence number and that on the repair; it schedules requests for all ofthis data, marks this message as received, and returns. On the other hand, if the sequence number of the request is less thanthe last known sequence number from the source, then the agent can be in one of three states: (1) it does not have this data,and has a request pending for it, (2) it has the data, and has seen an earlier request, upon which it has a repair pending for it,or (3) it has the data, and probably scheduled a repair for it at some time; after error recovery, its hold down timer (equal tothree times its distance to some requester) expired, at which time the pending object was cleared. In this last situation, theagent will simply ignore the repair, for lack of being able to do anything meaningful. All of these error recovery mechanismsare done in OTcl; recv_repr() invokes the instance procedure recv-repr{sender, msgid} to complete the loss recoveryphase for the particular message.Session Packets On receiving a session message, the agent updates its sequence numbers for all active sources, and computesits instantaneous distance to the sending agent if possible. The agent will ignore earlier session messages from a groupmember, if it has received a later one out of order.Session message processing is done in recv_sess(). The format of the session message is: 〈count of tuples in this message,list of tuples〉, where each tuple indicates the 〈sender id, last sequence number from the source, time the last session messagewas received from this sender, time that that message was sent〉. The first tuple is the information about the local agent 3 .2 Technically, recv_data() invokes the instance procedure recv data 〈sender〉〈msgid〉, that then invokes recv-data{}. The indirectionallows individual simulation scripts to override the recv{} as needed.3 Note that this implementation of session message handling is subtly different from that used in wb or described in [11]. In principle, an agent disseminatesa list of the data it has actually received. Our implementation, on the other hand, only disseminates a count of the last message sequence number per sourcethat the agent knows that that the source has sent. This is a constraint when studying aspects of loss recovery during partition and healing. It is reasonable toexpect that the maintainer of this code will fix this problem during one of his numerous intervals of copious spare time.315
36.4 Loss Detection—The Class SRMinfoA very small encapsulating class, entirely in C++, tracks a number of assorted state information. Each member of the group,n i , uses one SRMinfo block for every other member of the group.An SRMinfo object about group member n j at n i , contains information about the session messages received by n i from n j .n i can use this information to compute its distance to n j .If n j sends is active in sending data traffic, then the SRMinfo object will also contain information about the received data,including a bit vector indicating all packets received from n j .The agent keeps a list of SRMinfo objects, one per group member, in its member variable, sip_. Its method, get_state(intsender) will return the object corresponding to that sender, possibly creating that object, if it did not already exist. The classSRMinfo has two methods to access and set the bit vector, i.e.,ifReceived(int id)setReceived(int id)indicates whether the particular message from the appropriate sender, with id id was receivedat n i ,to set the bit to indicate that the particular message from the appropriate sender, with id id wasreceived at n i .The session message variables to access timing information are public; no encapsulating methods are provided. These are:int lsess_; /* # of last session msg received */int sendTime_; /* Time sess. msg. # sent */int recvTime_; /* Time sess. msg. # received */double distance_;/* Data messages */int ldata_; /* # of last data msg sent */36.5 Loss Recovery ObjectsIn the last section, we described the agent behavior when it receives a message. Timers are used to control when any particularcontrol message is to be sent. The SRM agent uses a separate class SRM to do the timer based processing. In this section,we describe the basics if the class SRM, and the loss recovery objects. The following section will describe how the classSRM is used for sending periodic session messages. An SRM agent will instantiate one object to recover from one lost datapacket. Agents that detect the loss will instantiate an object in the class SRM/request; agents that receive a request andhave the required data will instantiate an object in the class SRM/repair.Request Mechanisms SRM agents detect loss when they receive a message, and infer the loss based on the sequencenumber on the message received. Since packet reception is handled entirely by the compiled object, loss detection occurs inthe C++ methods. Loss recovery, however, is handled entirely by instance procedures of the corresponding interpreted objectin OTcl.When any of the methods detects new losses, it invokes Agent/SRM::request{} with a list of the message sequencenumbers that are missing. request{} will create a new requestFunction_ object for each message that is missing.The agent stores the object handle in its array of pending_ objects. The key to the array is the message identifier〈sender〉:〈msgid〉.316
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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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Page 281 and 282: $ns_ rtmodel This command defines
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Page 361 and 362: Chapter 40Worm ModelIn this chapter
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HTTP responsesclients servers Delay
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41.5 Commands at a GlanceThe follow
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• HTTP response size (bytes)• s
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Chapter 42Session-level Packet Dist
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42.1.2 Inserting a Loss ModuleWhen
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Delay and Loss Modules Each receive
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Chapter 43Asim: approximate analyti
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set n(1) [$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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