2. References
Awk – A Tutorial and Introduction
NS by Example nile.wpi.edu/NS/

3. Trace Analysis Tools

4. Awk utility Awk is an excellent filtering and reporting utility
A pseudo-C interpreter
Same C arithmetic
Supports associative arrays (array index can be a variable of any type)

5. Awk – Basic Structure pattern { action }
pattern specifies when action is performed
Awk is line oriented
Default pattern matches every line
Two other important patterns
BEGIN
END
M. Dahshan - TCOM5272

6. Awk – Basic Structure Example on an NS trace file Output
cbr
cbr
r cbr
BEGIN {print “Time\tSequence Number”} {print $2”\t”$11} END {print “DONE”}
Output
Time Sequence Number
DONE
M. Dahshan - TCOM5272

7. Calculating Packet Delay
BEGIN {
# simple awk script to generate end-to-end # packet lifetime statistics
# in a form suitable for plotting with xgraph
# Lloyd Wood, July 1999. #
highest_packet_id = 0; }
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8. Calculating Packet Delay{
action = $1;
time = $2;
node_1 = $3;
node_2 = $4;
src = $5;
flow_id = $8;
node_1_address = $9;
node_2_address = $10;
seq_no = $11;
packet_id = $12;
M. Dahshan - TCOM5272

9. Calculating Packet Delay
if ( packet_id > highest_packet_id ) highest_packet_id = packet_id;
# getting start time is not a problem, provided you're not starting
# traffic at 0.0.
# could test for sending node_1_address or flow_id here.
if ( start_time[packet_id] == 0 ) start_time[packet_id] = time;
# only useful for small unicast where packet_id doesn't wrap.
# checking receive means avoiding recording drops
if ( action != "d" ) {
if ( action == "r" ) {
# could test for receiving node_2_address or flow_id here.
end_time[packet_id] = time; }
} else {
end_time[packet_id] = -1;
M. Dahshan - TCOM5272

10. Calculating Packet Delay
END {
for ( packet_id = 0; packet_id <= highest_packet_id; packet_id++ ) {
start = start_time[packet_id];
end = end_time[packet_id];
packet_duration = end - start;
if ( start < end ) printf("%d %f\n", packet_id , packet_duration); }
M. Dahshan - TCOM5272

11. Calculate Average Delay
First, calculate packet delay
{ #increment number of lines num_lines++; #sum the delay values #column 2 is the packet delay sum_delay=sum_delay+$2; } END {print sum_delay/num_lines}
M. Dahshan - TCOM5272

12. Calculating Dropped Packets
BEGIN{dropped=0} {
action = $1;
if(action=="d")
dropped++; }
END{print dropped}
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13. Calculating Throughput
Throughput = total number of bytes received
BEGIN{dest=3} { action = $1; node2 = $4; packet_size = $6; if(action=="r" && node2=dest) throughput + = packet_size; } END{throughput}
M. Dahshan - TCOM5272

14. Calculating Jitter Jitter = difference between packet delays
First, calculate packet delay
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15. Calculating Jitter BEGIN {old_delay=0.0;} { delay = $2;
if(old_delay>0) jitter=delay-old_delay;
else jitter=0.0;
#if(jitter<0) jitter = -jitter;
old_delay = delay;
print $1 " " jitter; }
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16. cat, grep, wc
We can simplify processing by doing some pre-filtering using grep
We can also do some quick calculations by combining multiple small commands
Take the output of a command as an input to the next command (pipes)
M. Dahshan - TCOM5272

17. Print only CBR Traffic grep cbr out.tr
r cbr
cbr
cbr
cbr
cbr
r cbr
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18. Print CBR Traffic From 2 to 3
grep "2 3 cbr" out.tr
cbr
cbr
cbr
cbr
cbr
cbr
cbr
cbr
r cbr
cbr
M. Dahshan - TCOM5272

19. Print Only Received Packets
grep ^r out.tr
r cbr
r cbr
r cbr
r cbr
r cbr
r cbr
r cbr
r cbr
r cbr
r cbr
M. Dahshan - TCOM5272

20. Print CBR Received at Node 3
grep ^r out.tr | grep "2 3 cbr"
r cbr
r cbr
r cbr
r cbr
r cbr
r cbr
r cbr
r cbr
r cbr
r cbr
M. Dahshan - TCOM5272

21. Calculate Dropped Packets!
grep ^d out.tr | wc –l 18
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22. Activities
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23. Trace Analysis Example
Download the file Trace Analysis Example
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24. Activity 1: Calculate Packet Delay
Use the provided packet delay script to calculate the delay for CBR traffic only!
Save the output to a file cbr_delay.txt
Commands:
ns ns-simple-trace.tcl
grep cbr out.tr | awk -f pkt_delay.awk > cbr_delay.txt
M. Dahshan - TCOM5272

25. Activity 2: Calculate Jitter
Use the provided packet jitter script to calculate the delay for CBR traffic
Save the output to a file cbr_jitter.txt
Commands:
awk -f jitter.awk cbr_delay.txt > cbr_jitter.txt
M. Dahshan - TCOM5272

26. Activity 3: Plot Delay and Jitter
Use xgraph or gnuplot to plot the delay and jitter for CBR traffic on the same graph
For xgraph
xgraph cbr_delay.txt cbr_jitter.txt
M. Dahshan - TCOM5272

27. Activity 3: Plot Delay and Jitter
Using gnuplot
gnuplot
gnuplot>set key left top Right noreverse enhanced box
gnuplot>set xlabel "Packet ID"
gnuplot>set ylabel "Delay and Jitter (sec)"
gnuplot>plot “cbr_delay.txt" using 1:2 title “Packet Delay" with lines 1, “cbr_jitter.txt" using 1:2 title “Jitter" with lines 2
M. Dahshan - TCOM5272

28. Activity 4: Stochastic Fair Queue
Edit the ns-sample-trace.tcl script
Change the queue type from DropTail to SFQ
Save as ns-sample-trace-sfq.tcl
Recalculate delay, jitter and plot the results (cbr_delay_sfq.txt, cbr_jitter_sfq.txt)
Discuss your findings
M. Dahshan - TCOM5272

29. Activity 4: Random Early Detection
Edit the ns-sample-trace.tcl script
Change the queue type from DropTail to RED
Save as: ns-sample-trace-red.tcl
Recalculate delay, jitter and plot the results (cbr_delay_red.txt, cbr_jitter_red.txt)
Discuss your findings
M. Dahshan - TCOM5272