题意： 完成5道计算机网络问题

 解析 

q1：求B到F的最短路径，利用Dijkstra算法，先求B到邻节点的最短路径，为3（BC），再将BC看成一个节点求他们到其他邻节点的最短路径，为5（BCE），重复步骤，求得B到F的最短路径为7，注意更新节点的权值变化 q2：对于A，2^n-2>=2000,n>=11,所以MASK最小为11,子网掩码取21位，159.27.0.0/21 q3：数据段主要是用来建立主机端到端连接，包括TCP和UDP连接，数据被分割，这样可对每个数据段进行排序，以便在接收端按发送顺序重组数据流 

涉及知识点： 最短路径，计算机网络计算

COMP90007 Internet Technologies
Assignment 2
Semester 2, 2019
Due date: Oct 18th Friday 11:30am
This assignment is worth 5% of the total marks for the subject. This assignment has 5 questions.
The weighting of each question is shown beside the question. Answers must be submitted as a
PDF file via the COMP90007 Assignment 2 submission form in the LMS which will open close to
the submission time. Late submissions will attract a penalty of 10% per day (or part thereof).
Please ensure your name, user name and id are clearly presented. Submission should only
contain the question number and the answer (do not repeat the text of questions in your
submission). Questions can be answered by studying the material covered. All work presented
should be your original individual effort/work.
Question 1 (1 mark)
Consider a subnet in the following figure, with the weight of each edge as shown in the label.
The shortest path routing is used.
1) Compute the sink tree for node B using Dijkstra’s algorithm. Show your calculation and the
steps of adding all nodes to the sink tree. (It is recommended to use a table similar to the
one as shown on the Slide 9 of Week 6’s lecture)
2) What is the shortest path from B to F and its distance?
Question 2 (1 mark)
Suppose that four organisations A, B, C and D request 2000, 1700, 900, and 4000 addresses
respectively, and in that order. There are a large number of consecutive IP addresses available
starting at 159.27.0.0, which can be assigned to these four organisations. For each of these
organisations, give the first IP address assigned, the last IP address assigned, the number of
addresses allocated and the mask in the w. x. y. z /s notation.
Question 3 (1 mark)
Different applications care about different aspects of a network transmission. For the following
applications please annotate each bucket/aspect with three values, Low, Medium, High, where
High means a high need for quality for that aspect.
Question 4 (1 mark)
At Transport layer we use segments to send data across. Argue for using larger segments by
discussing briefly why larger segments could be beneficial. Then also argue why using small
segments may be beneficial.
Question 5 (1 mark)
In the following security protocol that we saw in class, discuss briefly what could go wrong with
the protocol if RA was not sent across from Alice to Bob. What fails in the protocol?