# 计算机网络代写 | SIT202 Computer Networks Problem Solving Report 1

SIT202 Computer Networks Trimester 2, 2019
Problem Solving Report 1 (due 11:59 pm Friday August 30th 2019) Total Marks = 45
This will be converted to 15% of total marks
General Marking Policies (if no specific policies are given):
▪ A full mark – mostly good explanation/s with appropriate names, components of each PDU, peer layer communications, direction of data flows with appropriate diagram
▪ 3⁄4 of full marks – good explanation, explained all steps of decapsulation/s with some error /inaccuracies
▪ a half mark – average explanation/s, with clear correct and incorrect aspects;
▪ 1⁄4 of full mark – the answer is largely incorrect, however some minor parts of
the explanations/s are correct;
▪ 0 mark – no parts of the answer are correct and/or there has been no attempt to
address any of the requirements of the question.
▪ No plagiarism: an allocation of a zero mark is to be given.
Question-1 (Chapter 18): 12 marks
1) In current classful addressing, there are 5 classes as shown in Fig. 18.18 (p. 531 of the textbook). There are 5 classes with variable-length leading bits as follows:
Class A: 0; Class B: 10; Class C: 110; Class D: 1110; Class E: 1111
Suppose that we wish to modify to accommodate 9 classes. What are 9 (variable-length) leading bits for them? [4 marks]
2) [8 marks] A classless address is given as 200.107.16.17/20
• Find the first and last addresses in the block (explain in detail how you can find them). [4 marks]
• Find the mask. [4 marks]

Question-2 (Chapter 20):
20 marks
Consider the network consisting of 5 nodes.
1) Find the distance vectors for all the nodes. [8 marks]
2) Can the maximum distance of the network (the maximum distance between any pair of different nodes, i.e., {A,C}, {A,D}, {B,C}, etc) be lowered if the distance between nodes B and E becomes 2? Please explain how you come to the answer (Yes or No). [4 marks]
A
1
BC
4
3
2
1
DE
3) Find the maximum distance of the network if
the link between nodes A and C is removed. In addition, discuss what is the performance loss after losing the link between nodes A and C. [8 marks]

Question-3 (Chapters 23 and 24): 13 marks
1) Choose “True” or “False” for each item [3 marks]
True or False
In the transport layer, port numbers are used to identify local computers.
For flow control, we need two buffers: one at the sending transport layer and the other at the receiving transport layer.
There are only connection-oriented protocols in the transport layer, while the network layer supports connectionless communication.
2) [6 marks] Suppose that the Go-Back-N protocol with 𝑚 = 3 and the sending window of size 7 is used to send packets. Let 𝑆 = 31, 𝑆 = 35, and
𝑅( = 33.
a. b.
c.
3) [4
a. b.
What are the sequence numbers of data packets in transit? [2 marks] What are the acknowledgement numbers of ACK packets in transmit? [2 marks]
If the sender’s process sends two more data packets to the sender’s transport layer and one ACK packet is received from the receiver’s transport layer, what are the updated values for 𝑆 and 𝑆 ? [2 marks]
marks] The following is part of a TCP header in hexadecimal format:
93E2 B017 0AB2 0000 …
What is the destination port number? [2 marks] What is the sequence number? [2 marks]
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