April 2000
NI222 : NETWORKS AND THE INTERNET

QUESTION 3

Total Marks: 15 Marks

• Question 1
• Question 2
• Question 4
• Question 5
• Cover Page

SUGGESTED SOLUTIONS
Solutions and allocated marks are indicated in green.
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(a)In a 1-way handshake host A sends a message to host B,and assumes that it is connected.Give a state diagram for this protocol,and a event diagram to show how it can fail.[4 marks ]

(b)Describe an advantage and a disadvantage of using a variable sliding window protocol rather than a normal sliding window protocol.[2 marks ]
Allows the window size to be changed as network conditions change,making the sliding window more flexible (1) The mechanism guarantees delivery at the cost of CPU processing and the network bandwidth (1).

(c)Explain how UDP preserves the message boundary defined by the application. [3 marks ]
The size of each write matches with the size of each read (1) Preserves the message boundary without joining two application messages together or dividing a single application message into parts (2)

(d)Convert the following event diagram into state diagram,using the standard
convention to distinguish outgoing messages from incoming messages,and to
describe outgoing messages sent in response to incoming messages.

[6 marks ]

(1) for identifying correct messages, up to a maximum of (4); (1) for using underlining and slash conventions correctly; (1) for identifying the correct process states