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# 计算机网络代做 CS 158A代写 计算机网络代写 计算机作业代写

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## Problem Set 1

Due: Tuesday, March 8 at 6 PM (BEFORE CLASS)

No late submission will be accpted to go through solutions during the class on the due date.

A submission must be made as a PDF file on Canvas.

### Problem 1 (0.5 pt each, no partial credit)

Carefully read the following statements. If the statement includes incorrect information, explain why it is wrong in one or two sentences. Otherwise, write “True.”

Problem 1.1

File Transfer Protocol has two modes: Active and Passive. When using the passive mode, a FTP client needs to initiate the data transfer channel with port 21.

Problem 1.2

A socket is a programing interface that provides data transfer as a service for a user application.

To identify the user application, it uses a port number and the host’s MAC address.

### Problem 2 Computer Networks: Overview (0.5 pt)计算机网络代做

Consider a packet which begins at end system A and travels over three links to a destination end system. These three links are connected by two packet switches.

Suppose now the packet is 1,200 bytes, the propagation speed on all three links is 2.5 × 100 km/s, the transmission rates of all three links are 10 Mbps (bps: bits per second), the packet switch processing delay is 4 msec, the length of the first link is 3,000 m, the length of the second link is 4,000 m, and the length of the last link is 2,000 m. For these values, what is the end-to-end delay assuming no queuing delays?

### Problem 3 UDP计算机网络代做

Problem 3.1 (0.5 pt)

Compute the 16-bit UDP checksum of a message consisting of the following two strings: 0110 0011 1010 1010 and 1100 0101 0010 0111.

Problem 3.2 (0.5 pt)

Let’s consider 4-bit checksum for simplicity. (Note that although UDP uses 16-bit words in computing the checksum, for this problem you are being asked to consider 4-bit sums.)

Alice sent a segment that contains three 4-bit strings: 0100, 0011, and 1111.

Bob received the segment and confirmed the 4-bit checksum is correct. However, the segment had actually experienced some bit flips. Find a minimal example of such bit flips that was not detected by the checksum. (Here, “minimal” means the least number of bit flips.)

### Problem 4 IP and Routing计算机网络代做

Problem 4.1

Consider a datagram network with the network address 10.5.0.128/25. Suppose a router uses longest prefix matching (of the host part) and has the following forwarding table:

Problem 4.1.1 (0.4 pt each, total 1.2 pt)

For each of the three interfaces, give the associated range of destination host addresses.

Problem 4.1.2 (0.2 pt each, total 0.6 pt)

For a subnet with each prefix, answer the number of user devices that can be accommodated.

Problem 4.2 (0.7 pt)

Consider the network shown below, and assume that each node initially knows the costs to each of its neighbors. Consider the distance-vector algorithm and show the distance table entries at node z (Show each step).

The prev: The next:

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