Marghoob Mohiyuddin Review of network performance metrics ns 2 ns 2 demo 1 Understanding network behavior Improving protocols Verifying correctness of implementation Detecting faults Monitor service level agreements Choosing provider Billing Link bandwidth capacity maximum rate in bps at which the sender can send data along the link Propagation delay time it takes the signal to travel from source to destination Packet transmission time time it takes the sender to transmit all bits of the packet Queuing delay time the packet need to wait before being transmitted because the queue was not empty when it arrived Processing Time time it takes a router switch to process the packet header manage memory etc 2 Throughput of a connection or link total number of bits successfully transmitted during some period t t T divided by T Link utilization throughput of the link link rate Delay Latency of bit packet file from A to B The time required for bit packet file to go from A to B Jitter Variability in delay Round Trip Time RTT Two way delay from sender to receiver and back Bandwidth Delay product Product of bandwidth and delay network storage capacity of 3 Network centric metrics Reliability queue lengths load etc Network service providers try to provide best possible service to an aggregate of traffic flows End user centric metrics Throughput packet loss etc Users concerned about the performance of specific applications Robustness of network elements Mean Time to Failure MTF Mean Time to Repair MTR Designing components of a network Router and switch metrics Offered load Should be handled by the network element Dropped traffic Effectiveness of the router switch Average queue lengths Queue management when queue large Link metrics Link bandwidth Routing sub system metrics Route stability Excessive fluctuations can lead to connectivity problems 4 End to end latency and jitter Jitter variation in delay Can help identify congestion in the path Effective throughput Packet loss Application throughput decreases with increasing packet loss Measurements gather data from a real network e g ping www berkeley edu realistic specific Simulations run a program that pretends to be a real network e g NS network simulator Nachos OS simulator Models analysis write some equations from which we can derive conclusions general may not be realistic Usually use combination of methods 5 Review of network performance metrics ns 2 ns 2 demo Discrete event network simulator Models network protocols Wired wireless satellite TCP UDP multicast unicast Web telnet FTP Ad hoc routing sensor networks Infrastructure stats tracing error models Multiple levels of detail in one simulator 6 To examine protocol in controlled environment Repeatable experiments Alternatives Experimentation operation details but limited scale limited flexibility Analysis can provide deeper understanding but ignores implementation details ns Network Simulator Executes Tcl scripts containing simulation setup and events nam Network AniMator Visualize ns output xgraph graph plotter Plot ns output Analyze Tcl script ns 2 Sim results nam 7 Model world as events Maintain queue of events ordered by time Main virtual simulated time Repeat Extract event at head set virtual time to event s time Process it If processing generates another event then add it to queue Each event takes predefined amount of virtual time arbitrary amount of real time Slow CPU makes simulation run slower in real time but does not change result Assuming a simple queue model Event at t 1 A B A and B two nodes on an ethernet A enqueues packet on the LAN Generates event at t 1 1 Event at t 1 1 LAN dequeues packet and triggers B 8 Traffic models and applications web FTP telnet constant bit rate Transport protocols unicast TCP Reno Vegas etc UDP multicast SRM Routing and queueing wired routing ad hoc routing and directed diffusion queueing protocols drop tail RED fair queueing etc Physical media wired point to point LANs wireless multiple propagation models satellite C for packet processing Simulator code Library of network and protocol objects Can add new protocols oTcl for control oTcl Object Tcl Tool Command Language User s command scripts Network topology protocols applications Simulation output specification In this course project only requires writing the oTcl part 9 Programming language used to setup simulation environment Object oriented Interpreted Used for Setting up topology Placing events Injecting events Tracing events variables set x 10 puts x is x expressions set y pow x 2 set y expr x x 3 control if x 0 return x else return expr x while x 0 puts x set x eval x 1 Assign values set x 0 Use values set x y Mathematical expression expr x x 2 Nested commands set x expr y 2 Printing puts hello x File operations set file1 open filename w Control if k 5 puts k 5 else puts k 5 for set i 0 i 5 incr i commands Procedures procedure arg1 arg2 Methods object method arg1 arg2 Comments start with a 10 proc fact x set ret 1 if x 2 for set i 1 i x incr i set ret expr i ret puts factorial of x is ret fact 5 factorial of 5 is 120 Creating the event scheduler Tracing Creating network topology Creating Transport Layer Agents Creating Applications Applications Events 11 Create scheduler Creates new simulator object store this in the var ns set ns new Simulator Schedule event ns at time event event any legitimate ns tcl commands Start scheduler ns run helloworld tcl Create a simulator put in var ns set ns new Simulator ns at 1 puts Hello World ns at 1 5 exit ns run c199 ns helloworld tcl c199 Hello World Schedule event print HelloWorld at time t 1 Run the simulator executing events Execute the script 12 Node creation set n0 ns node set n1 ns node Can also set node color n0 color black Links Queuing ns simplex link n0 n1 bandwidth delay queue type ns duplex link n0 n1 bandwidth delay queue type Queue type DropTail RED CBQ FQ SFQ DRR ns duplex link n0 n1 1Mb 10ms DropTail ns queue limit n0 n1 20 UDP Source set udp0 new Agent UDP Sink set null new Agent NULL Connect to nodes ns attach agent n0 udp0 ns attach agent n1 null Connect together ns connect udp0 null 13 TCP Source set tcp0 new Agent TCP Sink set sink0 new Agent TCPSink Connect to nodes ns attach agent n0 tcp0 ns attach agent n1 sink0 Connect source and sink ns connect tcp0 sink0 Creating traffic on top of TCP FTP set ftp new Application FTP ftp attach agent tcp ns at time ftp start Telnet set telnet new Application Telnet telnet attach agent tcp 14
View Full Document
Unlocking...