QoS in Network Simulator 2

Transcription

1 QoS in Network Simulator 2 This experiment provides experience in how to apply and simulate QoS mechanisms in communication networks by means of NS2. We focus on RSVP in this experiment. 1. RSVP in NS2 HowTo This section provides a fast overview on how to use RSVP in NS2 scenarios, see [1] Setting an RSVP Link between Two Nodes An RSVP link between two nodes, node_1 and node_2 is created with the following Tcl command: ns duplex-rsvp-link <node_1> <node_2> <bw> <delay> <reservable> <rsvp> <queue> <adc> <est> where: ns is an instance of the simulator. bw expresses the bandwidth of the link. delay stands for the link delay. reservable determines the amount of bandwidth able to be reserved by RSVP. rsvp stands for the bandwidth (bits per second) reserved for RSVP control messages. If this value is set to zero, all RSVP control messages will be transmitted as best effort packets. Otherwise, a WFQ class with the specified bandwidth will be reserved for RSVP control messages to avoid control messages loss. queue is the size of the queue (in bytes) assigned to serve best-effort packets. adc determines the used admission control algorithm. There are currently five admission control algorithms implemented [2], namely Parameter-based Simple Sum algorithm (Param), Measured Sum (MS), Hoeffding Bounds (HB), Acceptance Region-Tangent at Origin (ACTO) and Acceptance Region-Tangent at Peak (ACTP). est is the estimator used by measurement-based admission control algorithms. Currently, there are four different estimators implemented, namely Null (for Param), TimeWindow (for MS), ExpAvg (for HB) and PointSample (for ACTO and ACTP). Example: $ns duplex-rsvp-link $a $b 1Mb 10ms Param Null 1.2. Setting Up and Creation of RSVP Agents The following creates an RSVP-agent named rsvpagent and adds it to the node node_1. set rsvpagent [$node_1 add-rsvp-agent] Another way to add the rsvpagent to the node node_1 is the following: $node_1 add-rsvp-agent

2 1.3. TCL Commands The following lists some useful commands for RSVP Create a session: <rsvp-agent> session <destination> <flow-id> Release a session: <rsvp-agent> release <session-id> Send path messages <rsvp-agent> sender <session-id> <rate> <bucket> <ttl> Reserve bandwidth <rsvp-agent> reserve <session-id> <style> <flow descriptor list> Send a RESV CONFIRM object with the next reservation message <rsvp-agent> confirm <session-id> Get a list of all sessions in an agent: <rsvp-agent> sessions Set the status value for a session <rsvp-agent> set-status <session-id> <value> Get the status value of a session <rsvp-agent> get-status <session-id> 2. RSVP in NS2 Practice Assume the network provided in figure 1. All links have a bandwidth of 1 Mbit/sec. The delay on each link is 10 msec. 90% of each link bandwidth can be reserved by RSVP, while 100 bit/sec is reserved for RSVP control messages. Each queue of network nodes reserves 5000 bytes to serve best effort packets. Resources are reserved for two UDP sessions. One is between nodes 1 and 2, while the other is between nodes 0 and 5. The RSVP session between nodes 1 and 4 is observed during this experiment. We measure the sending rate (in kbit/s) and the bandwidth loss (in packets/s). The sending rate is stored in a file named rate.tr, while the bandwidth loss is stored in a file named loss.tr.

3 Figure 1: An example network operating RSVP 2.1. Measuring the Sending Rate and Bandwidth Loss During the experiment, the following should be done. 1. Run the file rsvp-scenario.tcl by typing ns rsvp-scenario.tcl. 2. See the scenario using nam. What do you notice? What kind of traffic do we have? 3. Present the measured sending rates and bandwidth loss using xgraph. Interpret the results. 4. Go to the Tcl script and try to highlight, how the sending rate as well as the bandwidth loss has been measured Impact of Sending Rate During the experiment, the following should be done. 1. Change the sending rate of the CBR source attached to node 1 between until bits/s (actual rate is bits/s). The change can be done by updating this command in the script <set r [define_cbr_traffic $n1 $n ]>. 2. After each change, run the simulation again and stores the results files. 3. See the measured rates for all sending rates values and interpret the results. 4. Do the same for the bandwidth loss Impact of Best Effort Traffic The following task aims at analyzing how best effort traffic affects RSVP session. For this purpose, do the following: 1. Build a normal UDP session with a CBR source sending 500 bytes packets each 5 ms between both nodes 1 and Change the rate of the normal UDP session and notice how this affects the sending rate as well as the bandwidth loss of RSVP session between 1 and 4.

4 3. TCL Script # Create the scheduler and define the nam file and where the sending rates as well as bandwidth loss will be stored. set ns [new Simulator] set nf [open out.nam w] set ratef [open rate.tr] set lossf [open loss.tr] $ns namtrace-all $nf # Define two colors, each will be used for an RSVP session $ns color 1 Blue $ns color 2 Red # Create network nodes set n0 [$ns node] set n1 [$ns node] set n2 [$ns node] set n3 [$ns node] set n4 [$ns node] set n5 [$ns node] # Write a procedure named "create_link" This procedure is used to create an RSVP connection between two nodes, namely src_node and dst_node proc create_link {src_node dst_node { global ns set rate 1Mb set delay 10ms set reservable 0.9 set rsvp_rate 100 set bo_queue_size 5000 $ns duplex-rsvp-link $src_node $dst_node $rate $delay $reservable $rsvp_rate $bo_queue_size Param Null; # create RSVP connections between network nodes create_link $n0 $n2 create_link $n1 $n2 create_link $n2 $n3 create_link $n3 $n4

5 create_link $n3 $n5 # create RSVP connections between network nodes set rsvp0 [$n0 add-rsvp-agent] set rsvp1 [$n1 add-rsvp-agent] set rsvp2 [$n2 add-rsvp-agent] set rsvp3 [$n3 add-rsvp-agent] set rsvp4 [$n4 add-rsvp-agent] set rsvp5 [$n5 add-rsvp-agent] # create a UDP association between src_node and dst_node with a cbr_rate proc define_cbr_traffic {src_node dst_node cbr_rate class { global ns set udp_src [new Agent/UDP] $udp_src set class_ $class $ns attach-agent $src_node $udp_src set cbr_src [new Application/Traffic/CBR] set cbr_interval set packet_size_unit 8; $cbr_src set packetsize_ [expr $cbr_rate*$cbr_interval/$packet_size_unit] $cbr_src set interval_ $cbr_interval $cbr_src attach-agent $udp_src set null_sink [new Agent/LossMonitor] $ns attach-agent $dst_node $null_sink $ns connect $udp_src $null_sink return "$cbr_src $null_sink" set r [define_cbr_traffic $n1 $n ] set cbr0 [lindex $r 0] set null0 [lindex $r 1] $null0 set name "rsvp" set r [define_cbr_traffic $n0 $n ] set cbr1 [lindex $r 0] set null1 [lindex $r 1] $null1 set name "norm" proc print-sessions { { global rsvp1 ns set sessions [$rsvp1 sessions]

6 set now [$ns now] puts "time = $now: sessions - $sessions" # write a procedure named "monitor" to measure the sending rates and bandwidth loss proc monitor {loss_monitor prev { global ns ratef lossf set name [$loss_monitor set name] set bytes [$loss_monitor set bytes_] set nlost [$loss_monitor set nlost_] set now [$ns now] set time [expr $now-$prev] if {$time!=0 { set rate [expr $bytes/$time*8/1000] set lrate [expr $nlost/$time] else { set rate 0 set lrate 0 puts "$name $now $rate Kbit/s" puts "$name $now $lrate pkt/s lost" puts $ratef "$now $rate" puts $lossf "$now $lrate" $loss_monitor set bytes_ 0 $loss_monitor set nlost_ 0 set period 0.05 $ns at [expr $now+$period] "monitor $loss_monitor $now" set flow_id0 1 set rsvp_session0 [$rsvp1 session $n4 $flow_id0] $ns at 0 "monitor $null0 0" $ns at 0 "monitor $null1 0" $ns at 0.01 "$rsvp1 sender $rsvp_session " $ns at 0.1 "$rsvp4 reserve $rsvp_session0 FF $n1" $ns at 0.2 "$cbr1 start" $ns at 0.35 "$cbr0 start" $ns at 1.8 "$cbr0 stop"

7 $ns at 1.9 "$cbr1 stop" $ns at 2.0 "finish" proc finish { { global ns nf ratef lossf $ns flush-trace close $nf close $ratef close $lossf exec nam out.nam & exit 0 $ns run 4. References [1] M. Greis. RSVP/ns: An implementation of RSVP for the network simulator ns-2. RSVP/ns Documentation, [2] S. Jamin, S. J. Shenker, P. B. Danzig, Comparison of Measurement-based Admission Control Algorithms for Controlled-Load Service", Proc. IEEE INFOCOM 97, April 97.