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Text: Computer Networking – A Top-Down Approach, Authors: Kurose & Ross

Chapter 7: Multimedia Networking

7.3 Assume an Internet phone application generates packets only during talk spurts. During a talk spurt the sender generates bytes at a rate of 1,000 bytes per second, and every 40 msecs the sender gathers bytes into chunks. Assume that RTP is used that will add a header to each chunk. In addition UDP and IP will be used. Suppose all headers (including RTP, UDP and IP) have a total length of h and an IP datagram is emitted every
40 msecs. Find the transmission rate in bits per second for the datagram generated by one side of the application.

7.4 Consider the procedure described in “Adaptive Playout Delay” for estimating average

delay di. Let r1 ? t1 be the most recent sample delay, let r2 ? t2

be the next most recent

sample delay, and so on. For a given audio application, suppose four packets have arrived

at the receiver with sample delays

r4 ? t4 ,

r3 ? t3 ,

r2 ? t2 , and

r1 ? t1 . Express the

estimate of delay d in terms of u and the four samples.

7.7 Is it possible for a CDN to provide worse performance to a host requesting a multimedia object than if the host has requested the object directly from the distant origin server? Please explain.

Chapter 8: Security in Computer Networks

8.3 Can you “decrypt” a hash of a message to get the original message? Explain.

8.4 Suppose that Bob receives a PGP message from Alice. How does Bob know for sure that Alice created the message?

8.5 Consider WEP for 802.11. Suppose that the data is 10101010 and the keystream is
11110111. What is the resulting ciphertext?

8.6. Using the monoalphabetic cipher in the textbook, encode the message “This is a hard problem.” Decode the message “rmij’u uamu xyj.”

8.7 Consider the RSA algorithm with p=5 and q=11. a. What are n and z?
b. Let e be 3. Why is this an acceptable choice for e?
c. Find d such that de=1 (mod z) and d<160.

Practical assignment

This assignment consists of programming a Pinger client. Please submit the following items in a ZIP file.

1) Java or Python source code;
2) Instructions on how to install and run your program;
3) A brief design document explaining your solution.

Note: I shall not provide remedial help concerning coding problems that you might have. Students are responsible for the setup of their own coding environment. Each student is also expected to debug their code.

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