Computer Networks, CS 514

Homework 4, 22 October 2013

This assignment is due no later than 6:20 p.m. on Tuesday, 5 November.

This homework assignment has six questions; answer all of them. Answers should no longer than half a page, or around 100 to 150 words. Please site references you use to answer your questions, including the textbooks you’re using.

Your homework may turned-in on paper or via rclayton@monmouth.edu by email. If you mail your assignment, please submit a printable document — a PostScript .ps or PDF .pdf document, for example — and not a source document — a Word .docx or Latex .tex document, for example. Make sure you mail a printable document by the deadline.

1. Network A uses IP without ARP; Network B uses IP with ARP. Explain the differences between networks A and B that enables A to use IP without ARP and requires B use IP with ARP.

2. A colleague of yours has developed a new byte-stuffing scheme that (your colleague claims) improves on the usual byte-stuffing scheme by including a count in the escape byte. Your colleague's escape byte is fc where f is a four-bit flag and c is a four-bit count plus one (for example, if c is 0010₂, then the count is 3).

   Describe one way in which your colleague's byte-stuffing scheme is better than the usual byte-stuffing scheme. Describe one way in which the usual byte-stuffing scheme is better than your colleague's byte-stuffing scheme.
3. You are given a bit string and are told that a) the bit string contains a positive number of 8-bit bytes and b) the bit string you've been given is the result of applying some bit-stuffing scheme S to another bit string.

   Is there a single question you can ask that will help you determine what S uses for the escape-byte value? If there is, give the question and describe how the answer helps you determine the escape-byte value. If there isn't any such question, justify your claim.

   Note: you cannot ask the questions “What is the escape-byte value?” and “What is the original bit string?”
4. Linking n LANs with bridges produces a network N_b. Linking the same n LANs with routers produces a network N_r. Even though N_b and N_r are made up of the same LANs, N_b and N_r have different characteristics. Explain the mechanisms by which bridges and routers produce these different networking characteristics.

   Note this question doesn't identify the different characteristics. A good quality answer will identify such characteristics as part of the answer.

5. Explain in what sense Ethernet provides congestion control. Explain in what sense Ethernet provides flow control.
6. Explain why it makes sense to choose a random-backoff value from a large, dispersed value set when there are a large number of colliding senders.