CMSC 417 Midterm #1 (Spring 1997)

(15 points) Define or explain the following terms:

count to infinity problem


virtual circuit vs. packet switched



(15 points) Consider using a 4khz channel and 16 discrete levels to send data.

  1. What is the maximum possible transmission rate if the channel is noiseless?
  2. What if the signal to noise ratio is 30dB?

(15 Points) A cellular phone system needs to accommodate many users. Explain how the system uses space, frequency, and time division multiplexing.

(20 Points) List the seven layers of the ISO/OSI reference model and for each layer provide an example of a function commonly performed at that layer.

(20 points) Consider routing in a network with 200 routers, and on average every router is connected to 4 other routers. Routing information is exchanged every 100msec. How much network bandwidth is used under link-state and distance vector routing to exchange this information. Assume sequence numbers are used to damp flood packets for link-state. Please explain any assumptions you make about the size of routing table entries.

(15 points) In a broadcast channel, link bandwidth is wasted due to multiple hosts trying to send at once and canceling each others communication. A simple model of this problem is that time is divided into discrete slots. If a network has n hosts, and the probability of any single host trying to use a slot is p, what fraction of slots are wasted due to collisions?