# 计算机网络代写 | SIT202 Computer Networks Problem Solving Report 3

SIT202 Computer Networks Trimester 2, 2019
Problem Solving Report 3 (due 11:59 pm Friday September 20th 2019) Total Marks = 25
This will be converted to 10% of total marks
1. [12 Marks] Consider a scenario where a web portal uses cookies to track the users and provides a customized view to the individual user based on the previously visited sites. The web portal sends a cookie to the browser which is stored in the browser at the client’s side along with the visited sites. This helps to keep track the previously visited pages of a client from different sites. Prepare a diagram illustrating how the cookie is used between a browser and the web portal when a user revisits the web portal and how the pages are retrieved from different webservers to provide a customized view to the user. Consider two different webservers for two visited sites, a web portal and a client in your diagram. Explain the steps of your diagram.
[Hints: Use the concepts in Example 26.1 and 26.8, other related topics from the text book and description provided above]
Marking guideline:
12 marks: Prepared diagram and explained well with all servers and client as mentioned, with request, response and cookies, retrieved pages from servers.
9 Marks: Answer has missing components or errors from any two of the following components (servers, client, portals, request, response, cookie, retrieved pages from servers) and corresponding error in the explanation.
6 Marks: Answer has missing components or errors from any four of the following components (servers, client, portals, request, response, cookie, retrieved pages from servers) and corresponding error in the explanation.
3 Marks: Answer has missing components or errors from any 6 of the following components (servers, client, portals, request, response, cookie, retrieved pages from servers) and corresponding error in the explanation.

2. [13 Marks] In the following diagram, a web client is communicating with a web server which opens a TCP connection at client’s end. The client is using an initial sequence number (ISN) 2048 with a port of 51000 and receiving window size of 2000. In response, server also opens a TCP connection with ISN 21732 and receiving window size of 4000, port 80. After connection establishment, client sends two data segments each of size 500 bytes. Then server responds in a single segment with 1000 bytes. Then client closes the connection, in response server also closes the connection.
Show all TCP segments during connection establishment, data transfer and connection termination between client and server (no segments are corrupted/dropped in the exchange). For each segment, write header information which should include port number, sequence number, acknowledgement number, values of all bits in the control field, window sizes and ranges of data bytes in the data section (as appropriate for the segment type). The header information of each segment needs to be written in a separate table. Please do not write header information in the diagram. This makes it harder to read the diagram. Instead, in the diagram, identify the segments as SYN, SYN+ACJK, ACK, Data, FIN, FIN+ACK for their type etc. In each table for header information of a segment, first row in the table should mention the type of a segment and a direction symbol (à or ß) from client to server or vice versa.
[Hints: Use the concepts in Figures 24.10 and 24.11, other related topics from the text book and description provided above]
Marking guide line: Total =13 Marks
Marks for each segment-1.44, then each component marks=segment mark/number of component in the segment
1. Connection establishment (11 component + 13 component + 13 component)
2. Data transfer ( 15 component + 15 component + 15 component)
3. Connection termination ( 13 component + 13 component + 13 component)

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