Ping application

Bonus problem [20 pts]
Instruction
Use the ping application from one of our lab machines to measure the time it takes for a packet to
reach the destination and receive a response, called the round-trip time (RTT). Do so for CS's web
server www.cs.purdue.edu and IUPUI's web server www.iupui.edu in Indianapolis. Select five
additional destinations: midwest, east coast, west coast, across the Atlantic, and across the Pacific.
Some web servers of universities may be configured to ignore ping messages but it is not difficult to
find many that will respond. For the 7 destinations, use a map to roughly estimate their physical
distance from Purdue. Use SOL to calculate lower bounds of RTT for these destinations. Compare the
lower bounds against the estimates obtained through ping. For each of the destinations, give your
thoughts on what may be the main factors that result in the discrepancy. For example, if your distance
estimate from Purdue is based on straight line distance, then the fact that communication lines follow
indirect routes through major communication hubs might be one such factor. Whether this is a major
factor you may determine by overestimating the physical distance from Purdue and checking if SOL
latency is significantly impacted. Submit your answer in a pdf file, lab1.pdf, under lab1/.
The Bonus Problem is completely optional. It serves to provide additional exercises to understand the
material. Bonus problems help more readily reach the 45% contributed by lab component to the
course grade.
Answer
Selected Destinations
Destination URL IP Address
Estimated
Physical
Distance
(km)
RTT
Lower
Bound
(ms)
Estimated
RTT (ms)
Purdue www.cs.purdue.edu 128.10.19.120 1 0.007 0.397
IUPUI www.iupui.edu 129.79.123.148 140 0.933 5.906
Midwest bulletin.case.edu 12.2.169.179 409 2.727 13.511
East Coast cs.nyu.edu 216.165.22.203 1090 7.267 25.779
West Coast www.cs.ucla.edu 164.67.100.182 2861 19.073 50.741
Cross the
Atlantic
www.manchester.ac.uk 130.88.101.57 6203 41.353 100.777
Cross the
Pacific
upd.edu.ph 202.92.128.226 13267 88.447 240.461
Discrepancy Explanation
Destination [Estimated RTT / RTT Lower Bound] Ratio
Purdue 56.71428571
IUPUI 6.330117899
Midwest 4.954528786
East Coast 3.547406082
West Coast 2.660357574
Cross the Atlantic 2.436993688
Cross the Pacific 2.718701595
From the ratio table, most of the discrepancy between the estimated RTT with ping command and the
lower bound of RTT will reduce if the physical distance between two places increases. It is possible
that when the physical distance is relatively short, the RTT is mainly subject to the overhead of the
devices I/O and routing. Conversely, if the physical distance is relatively long, the speed of
transmission would affect the RTT more.
Overall, the lower bound of the RTT is always much smaller than the estimated RTT. That is because,
usually, the route between the source and destination would not be a straight line. Also, the route will
not be directly connected generally. More routing means more overhead, possible queueing and
package losses, which greatly increases the RTT.
For the connection oversea, another factor of the impact on the RTT could be the limited resource of
international internet connectivity and the undersea cables.
To sum up, the estimated RTT will get closer to the lower bound if the length of the route is longer.
The factor includes the indirect routing, queueing and device overhead.