Networking course. Easy assignment!

Need solutions to those 9 answers.. This assignment is due on Sept 30!

 

Contact me for the questions. Coz it’s PDF and couldn’t upload it

Comp445– Fall 2013 Theory Assignment 1 – Page 1

COMP 445 – Fall 2013

Theory Assignment 1

1) Circuit Switching aims at providing a better service through the reservation of the circuit

(i.e. circuit is dedicated). Now, considering only the perspective of the communicating

users over a Circuit Switching network (i.e. you should not be concerned with the entire

utilization of the network or the advantages to other users), is it possible that Circuit

Switching may actually end up harming its users instead of providing a better service to

them. If yes, provide a scenario/case that shows that. If no, explain why this service will

indeed provide the best service to its users at all times.

2) With DSL ISPs, dedicated lines usually connect to the local offices to the location where

the service is provided (i.e. residential homes). In contrast, with Cable ISPs, the

connection is shared between multiple homes in a neighborhood. In spite of this

configuration that is clearly to the benefit of DSL users, service provided by Cable ISPs

may still be superior to the one provided by DSL providers. Explain the reasons behind

this. Further, if you are hired by a DSL provider, and taking into account that changes to

the company’s infrastructure (i.e. wiring) is quite costly, what would you propose in

order to speed up the provided service while balancing the cost.

3) HTP provides two connections methods: persistent and non-persistent. While there are

clear advantages of persistent-HTTP, it is rather unclear whether non-persistent can be of

any use. Conduct a small research to find out why these two modes of connections are

provided. In specific, you should find out some of the advantages and disadvantages of

each of them, hence justifying their concurrent existence.

4) A successful attack to the Internet DNS would be devastating. Explain what type of

attacks can be made towards DNS. Why, to-date, such attacks in practice have not been

successful? In your answer, you should consider caching in particular. Why such

technique has not only proven to provide better performance, which is its original goal,

but also protection against security attacks.

5) Perform a Traceroute between your machine and any other host/server on the Internet,

preferably an overseas server. Provide snapshots of what was returned and analyze the

returned information. In specific, you should comment on any behavior that looks either

different or unusual. Indicate the number of routers between your machine and the

targeted host/server.

Comp445 – Fall 2013 Theory Assignment 1 – Page 2

6) Suppose two hosts, A and B, are 10,000KM apart and are connected by a direct link of

rate R = 5 Mbps. Assume further that the propagation speed over the link is 2.5 x 10
8
, and

that the packets to be transferred are of size 2 Mbits.

a. What is the propagation delay to send one packet from A to B?

b. What is the transmission delay to send 8 packets from A to B?

7) Now assume some modifications to the network specified in Question 6 above, where 2

routers are installed between A and B at more or less equal distances. Further assume the

link from A to the first router has been replaced by another link of rate R=4 Mbps, the

link between the two routers was kept as before, and the link between the second router

and B was replaced by a link of rate R=6 Mbps. Assume negligible processing and

queuing delays in the routers.

a. What is the propagation delay to send one packet from A to B?

b. What is the total transmission delay to send 2 packets from A to B?

c. How much time is needed to send one file of size 20 Mbits from A to B?

8) BitTorrent uses a trading scheme referred to as tit-for-tat. While some researchers argued

particular deficiencies in that scheme, others argued that if it was not for tit-for-tat, it is

likely that BitTorrent would not even exist today. Explain both points of view. In other

words, you should indicate the disadvantages of the scheme, as well as why it is still

crucial to have such a scheme, or an alternative one, for BitTorrent to exist.

9) (Textbook Question P.22 – Page 177). Consider distributing a file F of size 15 Gbits to

N

peers. The server has an upload rate of us= 30 Mbps, and each peer has a download rate

of di = 2 Mbps and an upload rate of u. For N = 10, 100, and 1000 and u = 300 Kbps, 700

Kbps, and 2 Mbps, fill the following table by the minimum distribution time for each of

the combinations of N and u for both client-server distribution and P2P distribution.

Client Server

N

10 100 1000

u

300 Kbps

700 Kbps

2 Mbps

Peer to Peer

N
10 100 1000

u
300 Kbps
700 Kbps
2 Mbps