Computer Networks代写  IT assignment代写
Computer Networks
 
This assignment is designed to test your understanding of computer networks through problem solving, literature study, simple analysis and problem solving.
 
IMPORTANT:
Assignment Rules and Submission Policy
• This assignment is an individual assignment. Discussions are encouraged but copying/plagiarism is not permitted and will be penalised according to university and faculty guidelines.
• It should be completed in its entirety (i.e., all questions must be attempted.)
• You are allowed to use up to five typed pages to write your ass1 assignment. All margins must be no less than 2 centimetres, and a Times New Roman 12 point font or similar must be used. Oversized assignments will be penalized.
• The submission date for the assignment is Wednesday, August 7, 2013 (9:00 am).
• Hard-copy and e-mail submissions are not acceptable and will not be marked.
 
Note #1: Students who do not submit by the due date will have their mark reduced. The faculty rule states:
Work submitted late without documented approval of the Unit Chair will be penalized. Assignments that are submitted after the submission date will be subject to a mark penalty equal to 10% of the marks per day of the marks available for the piece of work, up to and including three days after the published due date. Assignments submitted more than three days after the published submission date will not be marked.
 
Note #2: All workings must be shown for all mathematic/numerical problems.
 
 
ASSIGNMENT TASKS
 
1. To provide structure to the design of network protocols, network designers organise protocols in layers. The 7 layer ISO OSI reference model and the 5 layer Internet protocol stack are examples.
 
a. Describe the main advantages and disadvantages of a layered model (2 points)
b. Describe in detail the layers of the OSI reference model (3 points)
c. Describe in detail the layers of the TCP/IP protocol stack (3 points)
d. Provide a functional comparison between the OSI layers and the TCP/IP layers (2 points)
 
 
2. As a packet travels from a source end system to a destination end system, it experiences different types of delay that can result in packet loss and degrading of throughput.
 
a. Explain the four main types of delay experienced by packets (4 points)
b. What is the relationship between average queuing delay and traffic intensity? (2 points)
 
 
3. Consider two hosts, A and B connected by a single link of rate R bps. Suppose that the two hosts are separated by m meters and suppose that the propagation speed along the link is S meters/sec. Host A transmits a packet of size L bits to host B.
 
a. Suppose host A begins to transmit the packet at time t = 0. At time t = L/R secs, where is the last bit of the packet? (1 point)
b. Suppose that the transmission delay is 12 secs and the propagation delay is 15 secs. At time t = 12 secs (transmission starts at t = 0), where is the first bit of the packet? (1 point)
c. Suppose S = 2.5 X 108 m/sec, L = 100 bits and R = 28 kbps. Find the distance m so that the propagation delay and the transmission delay are equal. (2 points)
 
 
4. Consider a message that is 15 x 106 bits that needs to be sent from a source S to destination D. The two end systems are separated by two intermediate routers. Each link along the path from S to D has a bandwidth of 3 Mbps. Ignoring propagation, queuing and processing delays, calculate
 
a. How long does it take to move the message from source S to the destination D? (1 point)
b. Suppose that the message is segmented in to 5000 equal size packets. At what time will the second packet be  fully received at the second router? (2 points)
c. How long does it take to move the message from S to D when segmentation is employed? (2 points)
 
 
5. Obtain the HTTP/1.1 specification (RFC 2616) from the Internet Engineering Task Force (IETF: www.ietf.org). Based on the specification answer the following questions:
 
a. What are the advantages of persistent HTTP connections? (3 points)
b. Explain the mechanism used for signalling between the client and the server to indicate that a persistent connection is being closed. Can the client, the server or both, signal the close of a connection (2 points)
c. Compare the GET, conditional-GET and partial-GET methods. (3 points)
d. What encryption services are provided by HTTP? (1 point)
 
6. Compare and contrast the client server model with the P2P model. (2 points)
 
7. List the services provided by DNS. (1 point)