581333-1 Data Communication I

Examination  26.9.2003

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

1. Packets  sent  by the sender to a  network  can arrive  corrupted to the receiver or they can disappear altogether
     a)  What  are  the reasons or factors causing corruption  and loss of packets?   (4 p)
     b) How can the receiver detect corrupted or lost packets? What different means and mechanisms
          can be used?  How does  the system recover  from  this kind of error situations? (8p)
     c) How do  Internet protocols IP, UDP and TCP  relate to errors  and  error situation recovery? 
         Or how do they try to prevent  packet corruption or loss ?(8p)

2.Answer the following questions
     a) What is meant by flow control? What means and mechanisms can be used for flow control?
          (5 p)
     b) What is meant by  congestion control? What means and mechanisms can be used for
          congestion control? (5 p)
     c) What is meant by flooding?  What problems there are in flooding?  What benefits does
          flooding give?  (5p)
     d) What is meant by fragmentation? Why is it needed? How does IP protocol (version 4)  relate
          to fragmentation? (5 p)

3. A computer science student Aimo Ahkera  creates an e-mail message during a lecture break
using a machine connected to the department network and sends it to his  friend Ulla Uuttera who is as  an exchance student in Australia. The email message includes  text and a picture taken during a beach party.  
     a)  What application layer functions and protocols  are needed to transfer the message from
          Aimo's mail application to Ulla's mail application? Explain also why  these protocols and
           functions are needed. (8 p)
     b) How does  TCP protocol participate in the message transfer from the sender  to the receiver?
         Draw a diagrams showing what TCP segments and in what  order are needed. (8 p)
     c) Draw a picture  that shows in which form ( = with what headers and trailers added) the email
         message is transferred in the application, transport, network  and link layers.(4 p)