Problems for Exercise 1 (18.-21.9.2001)

1. About nets and their technologies. Surf the web to find information.
   1. What networks and network services have you used yourself? What kind of experiences do you have from using network servises?
   2. What services does Helsinki University network provide for its students? List at least three services,
   3. What is the structure of the University Network? What different techologies are used in the network? Here it is enough just to give names or terms. It is not necessary to understand the technology.
   4. 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. Data transfer by bicycle
   1. A person bicycling carries five diskets with 1.6 Mbytes information each. The speed of the bicycle is 18 kms in an hour. For what distances does the cyclist transfer this information faster than a communication link of i) 9600 bps, ii) 10 Mbps (bps = bits per second)?
   2. Supposing the cyclist carries 5 two side DVD-disks, each holding 8.5 Gbytes of data. For what distances does the cyclist now transfer this information faster than a communication link of i) 9600 bps, ii) 10 Mbps?
   3. Couldn't it be a good idea to handle a great part of data communication by fast cyclists carring DVD disks in big bags? What are the drawbacks of this solution? Where would it fit, where not?

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?