rate $R$ bps$?$ Does this delay depend on packet length? Does this delay depend

on transmission rate?

R$19.$ 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 $R_1=500kbps,R_2=2Mbps,$ and $R_3=1Mbps.$

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 through$-$

put, 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 $.$

R$20.$ 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?

R$21.$ 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?

SECTION $1\mathrm{.}5$

R$22.$ 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?

R$23.$ What are the five layers in the Internet protocol stack? What are the principal

responsibilities of each of these layers?

R$24.$ What is an application$-$layer message? A transport$-$layer segment? A net$-$

work$-$layer datagram? A link$-$layer frame?

R$25.$ Which layers in the Internet protocol stack does a router process? Which lay$-$

ers does a link$-$layer switch process? Which layers does a host process?

SECTION $1\mathrm{.}6$

R$26.$ What is self$-$replicating malware?

R$27.$ Describe how a botnet can be created and how it can be used for a DDoS attack.

R$28.$ 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.