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Internetworking with TCP/IP: Pearson New International Edition

Douglas E. Comer

Chapter 11

Reliable Stream Transport Service (TCP) - all with Video Answers

Educators

Chapter Questions

Problem 1

TCP uses a finite field to contain stream sequence numbers. Study the protocol specification to find out how it allows an arbitrary length stream to pass from one machine to another.

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Problem 2

The text notes that one of the TCP options permits a receiver to specify the maximum segment size it is willing to accept. Why does TCP support an option to specify maximum segment size when it also has a window advertisement mechanism?

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Problem 3

Under what conditions of delay, bandwidth, load, and packet loss will TCP retransmit significant volumes of data unnecessarily?

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Problem 4

A single lost TCP acknowledgement does not necessarily force a retransmission. Explain why.

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Problem 5

Experiment with local machines to determine how TCP handles computer reboots. Establish a connection from machine $X$ to machine $Y$ and leave the connection idle. Reboot machine $Y$ and then force the application on machine $X$ to send a segment. What happens?

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Problem 6

Imagine an implementation of TCP that discards segments that arrive out of order, even if they fall in the current window. That is, the imagined version only accepts segments that extend the byte stream it has already received. Does it work? How does it compare to a standard TCP implementation?

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Problem 7

Consider computation of a TCP checksum. Assume that although the checksum field in the segment has not been set to zero, the result of computing the checksum is zero. What can you conclude?

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01:59

Problem 8

What are the arguments for and against automatically closing idle TCP connections?

Asma Venkitta
Asma Venkitta
Numerade Educator
00:59

Problem 9

If two application programs use TCP to send data but only send one character per segment (e.g., by using the push operation), what is the maximum percent of the network bandwidth they will have for their data with IPv4? With IPv6?

Bibi Naikbakht
Bibi Naikbakht
Numerade Educator

Problem 10

Suppose an implementation of TCP uses initial sequence number $I$ when it creates a connection. Explain how a system crash and restart can confuse a remote system into believing that the old connection remained open.

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Problem 11

Find out how implementations of TCP solve the overlapping segment problem. The problem arises because the receiver must accept only one copy of all bytes from the data stream even if the sender transmits two segments that partially overlap one another (e.g., the first segment carries bytes 100 through 200 and the second carries bytes 150 through 250).

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Problem 12

Trace the TCP finite state machine transitions for two ends of a connection. Assume one side executes a passive open and the other side executes an active open, and step through the three-way handshake.

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Problem 13

Read the TCP specification to find out the exact conditions under which TCP can make the transition from FIN WAIT-I to TIMED WAIT.

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Problem 14

Trace the TCP state transitions for two machines that agree to close a connection gracefully.

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Problem 15

Assume TCP is sending segments using a maximum window size of 64 Kbytes on a channel that has infinite bandwidth and an average round-trip time of 20 milliseconds. What is the maximum throughput? How does throughput change if the round-trip time increases to 40 milliseconds (while bandwidth remains infinite)? Did you need to assume IPv4 or IPv6 to answer the question? Why or why not?

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Problem 16

Can you derive an equation that expresses the maximum possible TCP throughput as a function of the network bandwidth, the network delay, and the time to process a segment and generate an acknowledgement. (Hint: consider the previous exercise.)

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00:54

Problem 17

Describe (abnormal) circumstances that can leave one end of a connection in state FIN WAIT-2 indefinitely. (Hint: think of datagram loss and system crashes.)

Adam Conner
Adam Conner
Numerade Educator
04:11

Problem 18

Show that when a router implements RED, the probability a packet will be discarded from a particular TCP connection is proportional to the percentage of traffic that the connection generates.

Pratyush Raitan
Pratyush Raitan
Numerade Educator

Problem 19

Argue that fast retransmit could be even faster if it used one duplicate ACK as a trigger. Why does the standard require multiple duplicate ACKs?

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Problem 20

To see if a SACK scheme is needed in the modern Internet, measure the datagram loss on a long-lived TCP connection (e-g., a video streaming application). How many segments are lost? What can you conclude?

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00:23

Problem 21

Consider a wireless router with a $3 \mathrm{Mbps}$ connection to the Internet and a (bloated) buffer of $256 \mathrm{MB}$. If two users are downloading movies and a third user tries to contact google.com, what is the minimum time before the third user receives a response?

Ashley High
Ashley High
Numerade Educator

Problem 22

In the previous exercise, does your answer change if the connection between the router and the Internet is 10 Mbps? Why or why not?

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