Problem 1 -5 Homework #1 Solution

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Description

Problem 1

`traceroute’ is a computer network diagnostic tool for displaying the route (path) and measuring transit delays of packets across an Internet Protocol (IP) network. In this problem, you will use the `traceroute’ command to understand how packets route to a destination.

  1. Run traceroute command to nd a route to `ucla.edu’. How many hops are there in between your local host to the destination? Copy and paste the result on your console in the answer box. (If you are using Windows Command Prompt, then use `tracert’ command instead.)

  1. Run traceroute command to nd a route to `columbia.edu’. Copy and paste the result into the answer box.

  1. Compare two results in terms of the number of hops and the delays.

Write your answer here

Problem 2

Host A is sending real-time voice over a packet-switched network. Host A converts analog voice to a digital 128 kbps bit stream on the y. Host A then groups 1,600 bytes into a packet. Assume that the 1,600 bytes packet already includes all headers. There is one link between Hosts A and B; its transmission rate is 3 Mbps and its propagation delay is 20 msec. As soon as Host A gathers a packet, it sends it to Host B. As soon as Host B receives an entire packet, it converts the packets bits to an analog signal. How much time elapses from the time a bit is created (from the original analog signal at Host A) until the bit is decoded (as part of the analog signal at Host B)? In this problem, do not consider acknowledgement (response) from Host B.

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Problem 3

Tow hosts, A and B are separated by 20,000 kilometers and are connected by a direct link of R = 2M bps.

Suppose the propagation speed over the link is 2:5 108meters=sec.

Consider sending a le of 800,000 bits from Host A to Host B. Suppose the le is sent continuously as one large message. What is the maximum number of bits that will be in the link at any given time?

  1. How long does it take to send the le, assuming it is sent continuously?

  1. Suppose now the le is broken up into 20 packets with each packet containing 40,000 bits. Suppose that each packet is acknowledged by the receiver and the transmission time of an acknowledgment packet is negligible. Finally, assume that the sender cannot send a packet until the preceding one is acknowledged. How long does it take to send the le?

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Problem 4

Alice and Bob are working remotely on a course project and are using git as the version control software.

Is it true that one must have GitHub/GitLab account to use git?

  1. What is(are) the command(s) to initialize a local git repository?

Do Alice and Bob both must initialize local git repository? If no, what are the alternative?

  1. Let’s consider that Alice modi ed the le server.cpp:

    1. What git commands Alice needs to save modi cations in the local git repository

    1. What git commands Alice needs to upload saved modi cations to GitHub

    1. What git commands Bob needs to get Alice’s changes and apply them to the local repository

  1. Let’s consider that both Alice and Bob modi ed the le server.cpp and Alice was rst to successfully upload saved modi cations (commit) to GitHub

    1. Can Bob upload his changes without any additional actions? If no, why?

    1. If actions needed, list git commands that Bob will need to use to share his modi cations with Alice.

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Problem 5

You will learn some basic usages of Vagrant in your projects.

  1. What is Vagrant mainly used for?

  1. What is VirtualBox used for?

  1. What is Vagrant le?

  1. List at least ve commands you can use with Vagrant.

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