COSC 3213: Computer Networks
Assignment # 1
Instructors: Marvin Mandelbaum
Review probability and chapters 1 and 2 before attempting the assignment. For instructions on submission
and due date, please refer to the home page of the course.
Problem 1: An alternative to a LAN is simply a big timesharing system with terminals for all users. Give
two advantages of a client-server system based on a LAN. Give two advantages of timesharing system.
Problem 2: Give two reasons for using layered protocols.
Problem 3: A collection of five routers is to be connected in a point-to-point subnet. Between each pair
of routers, the designers may put a high-speed line, a medium-speed line, or a low-speed line, or no line.
If it takes 100 ms of computer time to generate and inspect each topology, how long will it take to inspect
all of them to find the one that best meets the expected load?
Problem 4: A group of (2n – 1) routers are interconnected in a centralized binary tree with a router at
each tree node. Router i communicates with router j by sending a message to the root of the tree. The root
then sends the message back down to j. Derive an approximate expression for the mean number of hops
per message for large n, assuming that all router pairs are equally likely.
Problem 5: List two ways in which the OSI reference model and TCP/IP reference model are the same.
List two ways in which they are different.
Problem 6: The propagation delay is the time required for the energy of a signal to propagate from one
point to another.
a) Find the propagation delay for a signal traversing the following networks at the speed of light in cable
(2.3 x 108 m/s):
a circuit board
a metropolitan area
up and down to a geostationary satellite
2 × 30,000 km
b) How many bits are in transit during the propagation delay in the above cases if bits are entering