Data Communications I, Autumn 2000

Problems for Exercise 1 (18.-22.9.2000)

  1. Try to find, from web or other sources, answers to the following questions about networks. PLEASE, do not bother the network maintenance people!
    1. What logical networks are provided for students to use at the Computer Science Department, at the University of Helsinki, for all students in Finland by FUNET (Finnish University Net)?
    2. What kind of technology is used in these networks? Here it is enough just to give names or terms. It is not necessary to understand the technology.
    3. What kind of services do these networks provide for the students?

  2. Connection oriented, connectionless
    1. What is the main difference between connectionless and connection oriented data communications.
    2. Can a service be connectionless, though the network is circuit switched. Or connection oriented when the network is packet switched? Give reasons and examples.

  3. How is it possible that a message in a data communication network can
    1. totally disappear
    2. multiply
    3. pop up to a receiver much later than many of its followers (in principal even many days later?

  4. The capacity of a communication line is 1 Mbps and the transfer rate of data is 100 Kbps. Users typically first fetch data from the Internet and then read it. On average reading takes 90% of the time and data transfer only 10%
    1. If circuit switching is used how many users can, at the same time, use the line?
    2. What is the probability that all the users are really transferring data at the same time?
    3. What indications do these results give you about the efficiency of circuit switching and packet switching?

  5. Reference models
    1. What are the two reasons for using layered protocols?
    2. List two ways in which the OSI Reference model and the TCP/IP reference model are the same. Now list two ways in which they differ.
    3. Which of the OSI layers handles each of the following?
      * Breaking the transmitted bit stream into frames.
      * Determining which route through the network to use.

  6. Search the Web to find answers to the following questions.
    1. How many Internet standards exist?
    2. Find RFC 791. What is it about? When was it published?
    3. What companies and organizations of your home country are participating in the ATM Forum?
    4. Where can you find WAP standards WAP 191 and WAP 203. What do these standards standardize?
    5. What is IMT-2000?
    6. What does the ISO committee JTC 1/SC 6 standardize?