Questions

$1.$ List the available residential access technologies in your city. Mention your city and country. For each type of access, provide the advertised downstream rate, upstream rate, and monthly price.

$2.$ Describe the most popular wireless Internet access technologies today. Compare and contrast them.

$3.$ Suppose users share a $2$ Mbps link. Also suppose each user transmits continuously at $1$ Mbps when transmitting, but each user transmits only $20$ percent of the time

a$.$ When circuit switching is used, how many users can be supported?

b$.$ For the remainder of this problem, suppose packet switching is used. Why will there be essentially no queuing delay before the link if two or fewer users transmit at the same time? Why will there be a queuing delay if three users transmit at the same time?

c$.$ Find the probability that a given user is transmitting.

d$.$ Suppose now there are three users. Find the probability that at any given time, all three users are transmitting simultaneously. Find the fraction of time during which the queue grows.

$4.$ Some content providers have created their own networks. Describe Google$$s network. What motivates content providers to create these networks?

$5.$ Consider sending a packet from a source host to a destination host over a fixed route. List the delay components in the end$-$to$-$end delay. Which of these delays are constant and which are variable? Explain.

$6.$ Visit the Transmission Versus Propagation Delay interactive animation at the companion Web site. Among the rates, propagation delay, and packet sizes available, find a combination for which the sender finishes transmitting

before the first bit of the packet reaches the receiver. Find another combination for which the first bit of the packet reaches the receiver before the sender finishes transmitting. Explain why the values you got make sense.

$7.$ How long does it take a packet of length $1,000$ bytes to propagate over a link of distance $2,500$ km$,$ propagation speed $2\mathrm{.}5$ x $10^8$ m$/$s$,$ and transmission rate $2$ Mbps$?$ More generally, how long does it take a packet of length L to propagate over a link of distance d$,$ propagation speed s$,$ and transmission rate R bps$?$ Does this delay depend on packet length? Does this delay depend on transmission rate?

$8.$ Suppose Host A wants to send a large file to Host B$.$ The path from Host A to Host B has three links, of rates R$1=500$ kbps$,$ R$2=2$ Mbps$,$ and R$3=1$ Mbps$,$ respectively.

a$.$ Assuming no other traffic in the network, what is the throughput for the file transfer?

b$.$ Suppose the file is $4$ million bytes. Dividing the file size by the throughput, roughly how long will it take to transfer the file to Host B$?$

c$.$ Repeat $($a$)$ and $($b$),$ but now with R$2$ reduced to $100$ kbps$.$

$9.$ Suppose end system A wants to send a large file to end system B$.$ At a very high level, describe how end system A creates packets from the file. When one of these packets arrives to a router, what information in the packet does the router use to determine the link onto which the packet is forwarded? Why is packet switching in the Internet analogous to driving from one city to another and asking directions along the way?

$10.$ Visit the Queuing and Loss interactive animation at the companion Web site. What is the maximum emission rate and the minimum transmission rate? With those rates, what is the traffic intensity? Run the interactive animation with these rates and determine how long it takes for packet loss to occur. Then repeat the experiment a second time and determine again how long it takes for packet loss to occur. Are the values different? Why or why not?

$11.$ List five tasks that a layer can perform. Is it possible that one $($or more$)$ of these tasks could be performed by two $($or more$)$ layers?

$12.$ What are the five layers in the Internet protocol stack? What are the principal responsibilities of each of these layers?

$13.$ What is an application$-$layer message? A transport$-$layer segment? A network$-$layer datagram? A link$-$layer frame?

$14.$ Which layers in the Internet protocol stack does a router process? Which layers does a link$-$layer switch process? Which layers does a host process?

$14.$ What is self$-$replicating malware?

$15.$ Describe how a botnet can be created and how it can be used for a DDoS attack.

$16.$ Suppose Alice and Bob are sending packets to each other over a computer network. Suppose Trudy positions herself in the network so that she can capture all the packets sent by Alice and send whatever she wants to Bob; she can also capture all the packets sent by Bob and send whatever she wants to Alice. List some of the malicious things Trudy can do from this position.

$17.$

Design and describe an application$-$level protocol to be used between an automatic teller machine and a bank$$s centralized computer. Your protocol should allow a user$$s card and password to be verif