How to Calculate Network Mean Slow Down in NS2
To calculate the Mean Slowdown in ns2 has a series of steps to follow and these parameters is utilized to evaluate the degradation in performance experienced by network flows because of congestion or other network difficulties. The Mean Slowdown parameters related to the actual time taken for a flow or packet to be routed with the time it would have taken in an ideal, uncongested network scenario. It’s mostly utilized in fairness and congestion control studies to evaluate on how much a flow or packet has been “slowed down” because of the network congestion, routing delays, or other issues.
The below are the brief approaches to calculate the mean slowdown in ns2:
Steps to Calculate Network Mean Slowdown in NS2
To compute Mean Slowdown, we generally need two components:
- Ideal transmission time: The time it would take to route the packet or flow in an ideal, uncongested network like based on propagation delay and bandwidth.
- Actual transmission time: The time it actually takes for the packet or flow to traverse the network that involves latency because of congestion, queuing, and routing.
Formula for Mean Slowdown:
For each packet iii:
Slowdowni=Actual Transmission TimeiIdeal Transmission Timei\text{Slowdown}_i = \frac{\text{Actual Transmission Time}_i}{\text{Ideal Transmission Time}_i}Slowdowni=Ideal Transmission TimeiActual Transmission Timei
The Mean Slowdown is then the average slowdown via all packets:
Mean Slowdown=1n∑i=1nSlowdowni\text{Mean Slowdown} = \frac{1}{n} \sum_{i=1}^{n} \text{Slowdown}_iMean Slowdown=n1i=1∑nSlowdowni
Where:
- n is the total number of packets or flows.
- Actual Transmission Time is the time it takes for a packet to be routed in current network conditions (measured from the trace file).
- Ideal Transmission Time is the time it would have taken for the packet to traverse the network in best criteria (deliberate based on the link bandwidth and propagation delay).
- Set Up the NS2 Simulation:
Initially, we want to configure a simple simulation in which data packets are sent from a source to a destination, and then evaluate the actual transmission time of each packet.
Example TCL Script for Data Transmission:
# Create the simulator
set ns [new Simulator]
# Create two nodes: source and destination
set node_(0) [$ns node]
set node_(1) [$ns node]
# Create a duplex link between the nodes (1 Mbps bandwidth, 10ms delay)
$ns duplex-link $node_(0) $node_(1) 1Mb 10ms DropTail
# Attach UDP agents to nodes for sending and receiving data
set udp0 [new Agent/UDP]
set sink [new Agent/Null]
$ns attach-agent $node_(0) $udp0
$ns attach-agent $node_(1) $sink
$ns connect $udp0 $sink
# Set up CBR traffic on the UDP agent
set cbr0 [new Application/Traffic/CBR]
$cbr0 attach-agent $udp0
$cbr0 set packetSize_ 512 ;# Packet size in bytes
$cbr0 set rate_ 1Mb ;# Transmission rate
# Start and stop the traffic
$ns at 1.0 “$cbr0 start”
$ns at 10.0 “$cbr0 stop”
# Enable tracing to capture packet transmission and reception
set tracefile [open out.tr w]
$ns trace-all $tracefile
# End the simulation after 12 seconds
proc finish {} {
global ns tracefile
$ns flush-trace
close $tracefile
exit 0
}
# End simulation at 12 seconds
$ns at 12.0 “finish”
In this simulation:
- The source node transmits packets at a rate of 1 Mbps over a link with 1 Mbps bandwidth and 10 ms propagation delay.
- The destination node receives the packets, and the actual transmission time can be dignified using the trace file.
- Trace File Overview:
Once the simulation completed, NS2 created a trace file (out.tr) that logs packet events like transmission and reception. To estimate the actual transmission time, we can monitor when each packet is sent and received.
Example Trace File Entries:
s 2.000000000 _0_ AGT — 512 cbr 0 0.0 1.0 1.0
r 2.010000000 _1_ AGT — 512 cbr 0 0.0 1.0 1.0
s 3.000000000 _0_ AGT — 512 cbr 1 0.0 2.0 2.0
r 3.010000000 _1_ AGT — 512 cbr 1 0.0 2.0 2.0
- s: Packet sent.
- r: Packet received.
- 2.000000000: Event time (in seconds).
- 0 and 1: Node IDs (source node _0_ and destination node _1_).
- 512: Packet size in bytes.
- Calculate Actual and Ideal Transmission Times:
- Actual Transmission Time is the time difference between when a packet is sent and when it is received.
Actual Transmission Timei=Reception Timei−Transmission Timei\text{Actual Transmission Time}_i = \text{Reception Time}_i – \text{Transmission Time}_iActual Transmission Timei=Reception Timei−Transmission Timei
- Ideal Transmission Time can be estimated using the link bandwidth and propagation delay. For a 512-byte packet routed over a 1 Mbps link with a 10 ms propagation delay:
Ideal Transmission Timei=Transmission Delay+Propagation Delay\text{Ideal Transmission Time}_i = \text{Transmission Delay} + \text{Propagation Delay}Ideal Transmission Timei=Transmission Delay+Propagation Delay Transmission Delay=Packet Size (in bits)Link Bandwidth (in bps)=512×81×106=0.004096 seconds\text{Transmission Delay} = \frac{\text{Packet Size (in bits)}}{\text{Link Bandwidth (in bps)}} = \frac{512 \times 8}{1 \times 10^6} = 0.004096 \, \text{seconds}Transmission Delay=Link Bandwidth (in bps)Packet Size (in bits)=1×106512×8=0.004096seconds Ideal Transmission Timei=0.004096+0.010=0.014096 seconds\text{Ideal Transmission Time}_i = 0.004096 + 0.010 = 0.014096 \, \text{seconds}Ideal Transmission Timei=0.004096+0.010=0.014096seconds
- AWK Script to Calculate Mean Slowdown:
We can utilize an AWK script to compute the actual transmission time for each packet and compare it with the ideal transmission time to estimate the slowdown. The mean slowdown can then be estimated by averaging the slowdown values for all packets.
AWK Script to Calculate Mean Slowdown:
BEGIN {
total_slowdown = 0;
packet_count = 0;
ideal_time = 0.014096; # Ideal transmission time (in seconds)
}
# Record the transmission time for each packet
$1 == “s” && $4 == “_0_” && $7 == “cbr” {
packet_time[$10] = $2; # Store the send time indexed by packet ID
}
# Calculate the actual transmission time and slowdown for each received packet
$1 == “r” && $4 == “_1_” && $7 == “cbr” {
actual_time = $2 – packet_time[$10]; # Actual transmission time
slowdown = actual_time / ideal_time; # Slowdown for this packet
total_slowdown += slowdown;
packet_count++;
}
END {
mean_slowdown = total_slowdown / packet_count;
print “Mean Slowdown: ” mean_slowdown;
}
This script:
- Records the transmission time for each packet.
- Computes the actual transmission time when a packet is received.
- Calculates the slowdown as the ratio of the actual transmission time to the ideal transmission time.
- Averages the slowdowns to estimate the mean slowdown.
- Running the AWK Script:
Save the AWK script as mean_slowdown.awk, and then execute it on the trace file created by NS2:
awk -f mean_slowdown.awk out.tr
- Interpreting Results:
The script will output the mean slowdown that denoted the average factor by which packets were delayed that related to their ideal transmission times.
Example output:
Mean Slowdown: 1.2
This means that, on average; packets took 1.2 times longer to be routed compared to the ideal, uncongested scenario.
- Conclusion:
To compute Mean Slowdown in NS2:
- Set up the simulation to transmit packets from a source to a destination.
- Capture transmission and reception times in the trace file.
- Calculate actual transmission times using the trace file and ideal transmission times according to the link properties.
- Compute the slowdown for each packet and estimate the mean slowdown using an AWK script.
Over the structure and thorough guide you can capable to know and to calculate the Mean Slowdown in the uncongested network environment. We plan to deliver more information regarding the Mean Slowdown in further pages.
Calculating the Network Mean Slow Down in NS2 can be quite challenging. We encourage you to stay connected with us, as we are here to provide guidance for optimal results. Our team specializes in networking parameter analysis, and we guarantee the best outcomes. If you need assistance with thesis ideas or topics, please do not hesitate to reach out to us.