582202 Introduction to Data Communication (4 cr, 2 cu)

Separate examination 17.11.2006

Write the name of the course, date, your name, student number and signature on every separate sheet. Books and calculators are not allowed.

1. ADDRESSES [18 p]
   1. Explain what kind of addresses are used in the different layers of the TCP/IP stack. (10 p)
   2. How do the different layers get to know the address that is used in the layer below in order to be able to use its services? (8 p)

2. ETHERNET [18 p]
   1. How does a station in a traditional Ethernet using the CSMA/CD protocol proceed when it wants to send a frame? Show how the stations A, B and C handle the situation where station A is sending, and during the sending of A:s frame stations B and C want to start sending. Explain the functionality until all the stations have succeeded to send their frame without collisions. (10 p)
   2. An Ethernet switch has interfaces to several Ethernet segments. How does the switch know into which interface it should send the frame. What information is needed, how this information is collected and stored? What does the switch do when it does not know which interface to use to reach the receiver? (8 p)

3. EMAIL IN THE INTERNET [24 p]
   Student A. Innokas at the University of Helsinki sends a short email message to his friend B. Eager who studies in London.
   1. What happens in the application layer? What application layer protocols are used and when are they used, so that the message composed by A. Innokas can be delivered to the mailbox of B. Eager and that he can read the message from his home PC? What messages are sent by these protocols? (Not necessary to know the exact format of the messages. It is enough to tell the meaning.) (10 p)
   2. What happens in the transport layer? What transport layer segments and in which order are needed to transport the messages of the application layer? (10 p)
   3. What is the role of the network layer in transferring the email message? (4 p)