2023年6月24日发(作者：)

CHAPTER 3: TRANSPORT LAYER

1.

A transport-layer protocol provides for logical communication between ___C_.

A.

Routers

B.

Hosts

C.

Application processes

D.

End systems

2.

Transport-layer protocols run in __D__.

A.

Servers

B.

Clients

C.

Routers

D.

End systems

3.

In transport layer, the send side breaks application messages into ___B_, passes to

network layer.

A.

Frames

B.

Segments

C.

Data-grams

D.

bit streams

4.

The receive side of transport layer reassembles segments into messages, passes to

__A__layer.

A.

Application

B.

Networking

C.

Physical

D.

MAC

5.

Services provided by transport layer include __C__.

A.

HTTP and FTP

B.

TCP and IP

C.

TCP and UDP

D.

SMTP

6.

Which of the following services is not provided by TCP?D

A.

In-order data transfers

B.

Reliable data transfers and flow controls

C.

Congestion controls

D.

Delay guarantees and bandwidth guarantees

7.

These two minimal transport-layer services----___A_ and ____----are the only two

services that UDP provides

A.

process-to-process data delivery, error checking

B.

congestion control, reliable data transfer

C.

flow control, congestion control

D.

In-order data transfer, error checking 8.

UDP offers which of the following benefits relative to TCP?C

A.

UDP guarantees that Individual packets of a transmission will arrive “in order”

B.

UDP supports a self-regulating “throttle” feature that prevents network

saturation

C.

UDP consumes fewer computer resources by not maintaining connection state

D.

None of the above

9.

Which of the following applications normally uses UDP services?B

A.

SMTP

B.

Streaming multimedia

C.

FTP

D.

HTTP

10.

The job of gathering data chunks, encapsulating each data chunk with header

information to create segments and passing the segments to the network is called

__A__.

A.

multiplexing

B.

de-multiplexing

C.

forwarding

D.

routing

11.

This job of delivering the data in a transport-layer segment to the correct socket is

called _B___.

A.

multiplexing

B.

de-multiplexing

C.

forwarding

D.

routing

12.

Port number’s scope is ___B_ to ____.

A.

0, 1023

B.

0, 65535

C.

0, 127

D.

0,255

13.

The port numbers ranging from __C__to ____ are called well-known port number

and are restricted.

A.

0, 127

B.

0, 65535

C.

0, 1023

D.

0,255

14.

The UDP header has only four fields, they are__A__.

A.

Source port number, destination port number, length and checksum

B.

Source port number, destination port number, source IP and destination IP

C.

source IP, destination IP, source MAC address and destination MAC address

D.

source IP, destination IP, sequence number and ACK sequence number

15.

The field of Length in UDP segment specifies the length of ___B_. A.

the UDP segment, not including the header

B.

the UDP segment, including the header

C.

the UDP segment’s header

D.

the Length field

16.

Which of the following about TCP connection is not correct?A

A.

It is a broadcast connection

B.

It is a point-to-point connection

C.

It is a pipelined connection

D.

It is a full duplex connection

17.

In the following four descriptions about MSS and MTU, which one is not correct?C

A.

The MSS is typically set by MTU

B.

The MSS is the maximum size of the TCP segment including headers

C.

The MSS is the maximum amount of application-layer data in the segment

D.

The MTU means the largest link-layer frame

18.

__A__ is the byte stream number of first byte in the segment.

A.

Sequence number

B.

ACK number

C.

Checksum

D.

port number

19.

__B__ is the byte sequence numbers of next byte expected from other side.

A.

Sequence number

B.

ACK number

C.

Checksum

D.

port number

20.

In the following four options, which one is correct?D

A.

Suppose that the last SampleRTT in a TCP connection is equal to 1 sec. Then

the current value of TimeoutInterval will necessarily be≤1 sec

B.

The timeout should be less than the connection’s RTT

C.

Suppose that the last SampleRTT in a TCP connection is equal to 1 sec. Then

the current value of TimeoutInterval will necessarily be≥1 sec

D.

The variations in the SampleRTT are smoothed out in the computation of the

EstimatedRTT

21.

There are two 16-bit integers: 1110 0110 0110 0110, 1101 0101 0101 0101. Their

checksum is__A__.

A.

0011

B.

1100

C.

11111

D.

1000

22.

Suppose host A sends host B one TCP segment with sequence number 418,

acknowledgement number 571, and 4 bytes of data. Then the sequence number in

the acknowledgement to this segment is _____C____ A.

422 B. 418 C. 571 D. 575

23.

Because TCP only acknowledges bytes up to the first missing byte in the stream,

TCP is said to provide__D__.

A.

positive ACKs

B.

Selective acknowledgements

C.

3 duplicate ACKs

D.

Cumulative acknowledgements

24.

If we define N to be the window size, base to be the sequence number of the oldest

unacknowledged packet, and next-seq-num to be the smallest unused sequence

number, then the interval [nextseqnum,base+N-1] corresponds to packet that

__A__.

A.

can be sent immediately

B.

have already been transmitted and acknowledged

C.

cannot be used

D.

have been sent but not yet acknowledged

25.

Which of the following is not a pipelining protocol.A

A.

Rdt1.0

B.

Go-Back-N

C.

Selective repeat

D.

TCP

26.

What is the main difference between stop-and-wait and pipelined reliable data

transfer protocol?B

A.

The pipelined protocol uses the NAK packets, whereas in the stop-and-wait

protocol senders always wait for ACK packets.

B.

With the pipelined protocol, the sender can send several packets in row,

whereas in the stop-and-wait protocol the sender cannot send the packets in

row.

C.

With the pipelined protocol, the receiver must send one ACK for several

packets (cumulative ACK), whereas in the stop-and-wait protocol the receiver

can not send the cumulative ACK.

D.

The pipelined protocol uses timeouts, whereas the stop-and-wait protocol does

not use the timeout.

27.

Fast retransmit means in the case that __D__ duplicate ACK-s are received, the

TCP sender resend segment before timer expires.

A.

6

B.

5

C.

4

D.

3

28.

__B__ is a speeding-matching service---matching the rate which the sender is

sending against the rate at which the receiving application is reading.

A.

congestion control

B.

flow control

C.

sliding-window control

D.

variable control

29.

TCP provides flow control by having the sender maintain a variable called the

__D__.

A.

buffer

B.

Congestion window

C.

Sliding window

D.

Receive window

30.

Provided RcvBuffer = 20, LastByteRcvd = 20, LastByteRead = 15, then

RcvWindow=__B__.

A.

14

B.

15

C.

16

D.

10

31.

In the following four descriptions about TCP connection management, which one

is not correct?D

A.

Either of the two processes participating in a TCP connection can end the

connection

B.

If the FIN bit is set to 1, it means that it wants to close the connection

C.

In the first two step of the three-way handshake, the client and server randomly

choose an initial sequence number

D.

In the three segments of the three-way handshake, the SYN bit must be set to

1

32.

How does TCP sender perceive congestion?D

A.

Through a timeout event

B.

Through a receiving duplicate ACK-s event

C.

Both A and B

D.

Either A or B

33.

There are two states in TCP congestion control, which are _C___.

A.

safe start and congestion abandon

B.

safe start and congestion avoidance

C.

slow start and congestion avoidance

D.

slow start and congestion abandon

34.

In TCP, the timeout interval is a function of:A

A.

estimated RTT at the sender B. MSS and the overhead of a segment

B.

the size of buffer at the receiver D. the size of sending window

35.

In a TCP connection, there is timeout event when the value of threshold is 32 and

the size of congestion window is 16. According to the TCP congestion control

policy, the new value of threshold and the new size of congestion window should

be ______C__, respectively. A.

16, 8 B. 24, 8 C. 8, 1 D. 16, 1