Emerging Internet Technologies
Harish Sethu
Department of Electrical and Computer Engineering
Drexel University
Exercises
1. If you were required to build a network exclusively for communications by fax,
would you choose packet switching or circuit switching?
2. Visit the web site of the IETF, and find out what is an RFC.
3. Routers in the Internet discard packets when there is congestion, which occurs often
enough. The e-mails you send, however, are rarely ever lost. How come?
4. In an output-queued switch, do you think larger output buffers will yield better
performance?
5. In an input-queued switch, can you eliminate head-of-line blocking if you had input
buffers of infinite size?
6. Given a distance-vector routing algorithm and a link-state routing algorithm, which
do you think requires less memory in the router?
7. A computer is connected to a network through a link of bandwidth equivalent to 2
million packets per second. Assume that all packets are of equal length, and each
token corresponds to one packet. A new token is generated every microsecond, and
the bucket is initially filled to capacity with 1 million tokens. How long can the
computer transmit at the full rate of 2 million packets per second?
8. Upon detecting congestion, a TCP sender backs off by reducing its rate. However,
TCP is something that runs on your computer and you are free to modify the software
to continue sending at whatever rate you choose. Will you get better performance
from the network with this modification? How about if the TCP standard itself were
to be modified and everyone used this new version of TCP?
9. You have to distribute 10 candies among 3 kids who you feel all have the same rights
to the candies. The first kid demands to have 3 candies, the second demands 5 and the
third demands 8. If you were to use the notion of fairness used in the Internet, how
would you distribute the candies?
10. An application using guaranteed service in the Integrated Services model specifies a
TSpec consisting of token bucket parameters, and an RSpec in terms of the bandwidth
alone. Can this application receive a guaranteed delay bound? Explain how.
11. Why do you think RSVP allows its reservation states to expire unless refreshed
periodically? Explain your answer.
12. Why do you think RSVP was explicitly designed to support multicast?
13. While transmitting compressed audio and video, some packets are much more
important to the quality of the playback than some other packets. Explain how you
will exploit this in a Differentiated Services Internet.
14. If every flow’s traffic was extremely smooth (without any sudden increase or
decrease in the sending rate), which do you think is a better model, Integrated
Services or Differentiated Services?
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15. Since MPLS allows explicit routing, can you use this feature to provide QoS to a flow
by always selecting a route that will meet the requirements? Explain your answer
with arguments.
16. All packets belonging to the same flow can use the same label through the entire path
of the network, which can certainly offer some convenience in traffic management.
Speculate on why MPLS does not require that the outgoing label be the same as the
incoming label.
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