2023年7月9日发(作者：)

I. Multiple Choice

1-5 ADBAC

6-10 AAABA

11-15 ABAAA

16-20 BAABA

21-25 BACAA

26-30 ABABA

31-36 BDDAAC

II. True or False

TFTFT

III. Answer Briefly

Suppose Client A initiates a Telnet session with Server S. At about the same

time ,Client B also initiates a Telnet session with Server S. Provide possible source

and destination port numbers for

1) The segments sent from A to S.

source port:567

destination port:23

2) The segments sent from B to S.

source port:423

destination port:23

3) The segments sent from S to A.

source port:23

destination port:567

4) The segments sent from S to B.

source port:23

destination port:423

5) If A and B are different hosts, is it possible that the source port number in the

segments from A to S is the same as that from B to S 因为A和B在不同的主机上，那么端口号是有可能相同的。

6) How about if they are the same host

在同一台主机上不同进程的端口号肯定不同

Host A and Host B are communicating over a TCP connection, and Host B has already

received from A all bytes up through byte 358. Suppose Host A then sends two segments

to Host B back-to-back. The first and second segments contain 50 and 80 bytes of data,

respectively. In the first segment, the sequence number is 359, the source port number

is 1028, and the destination port number is 80. Host B sends an ack whenever it

receives a segment from Host A.

1) In the second segment sent from Host A to B, what are the sequence number, source

port number, and destination pot number

sequence number:359 + 50 = 409

source port:1028

destination port:80

2) If the first segment arrives before the second segment, in the acknowledgment of

the first arriving segment, what is the acknowledgment number, the source port number,

and the destination port number

ack:409

source port:80

destination port:1028

3) If the second segment arrives before the first segment, in the acknowledgment of

the first arriving segment, what is the acknowledgment number

ack:359,因为没有收到第一个的ack，接收方期待收到的是359，所以发送的是359 4) Suppose the two segments sent by A arrive in order at B. the first acknowledgment

is lost and the second acknowledgment arrives after the first timeout interval. Draw a

timing diagram, showing these segments and all other segments and acknowledgements

sent. (Assume there is no additional packet loss.) For each segment in your figure,

provide the sequence number and the number of bytes of data; for each acknowledgment

that you add, provide the acknowledgment number.

The client A wants to request a Web page from Server B. Suppose the URL of the

page is and also it wants to receive French version of object. The time-sequence

diagram is shown below, please fill in the blanks.

Packet 1 to Packet 3 are TCP connection’s segment, then:

Packet 1: SYN flag bit = 1

ACK flag bit = 0

Sequence number = 92 Packet 2: SYN flag bit = 1

ACK flag bit = 1

Sequence number = 100

Packet 3: SYN flag bit = 0

ACK flag bit = 1

Sequence number = 93

.45 Fill in the value of the congestion window size (number of segments) for each

transmission round. Assume the threshold starts at 30 segments and the following events

occur:

− triple duplicate ACK during round 10

− timeout during round 12

− triple duplicate ACK during round 14

− timeout during round 22

Round

1

2

3

4

5

6

7

Congestion Window Size

1

2

4

8

16

32

33

Round

14

15

16

17

18

19

20

Congestion Window Size

2

1

2

3

4

5

6 8

9

10

11

12

13

34

35

36

18

19

1

21

22

23

24

25

26

7

8

1

2

4

1

− timeout during round 25

Host A wants to send a 12KB file F over a TCP connection. Several assumptions:

− This TCP connection uses the slow-start congestion control scheme with an initial

THRESHOLD value of 4 KB

− The MSS is 1KB.

− The receiver’s advertised window is initially 4 KB.

− Unless indicated otherwise, all segments were received properly and received in

the same order as they were sent

− The receiver will send ACK immediately, once receiving one data segment.

− The receiver will buffer all the out-of-ordered segments.

− It takes the sender 10 ms to “push” the segment onto the network. This means

that if the first data segment is pushed onto the network starting at time 0, then the

second segment can started to be pushed onto the network at 10 ms.

− Unless indicated otherwise, each successfully transmitted segment has a round trip

time of exactly 60ms (30 ms each way). This time includes transmission time.

− The timer on host A of this TCP connection is always set as 100 ms.

− The seq number and ack number of the first data segment are 0 and 100,

respectively.

− Under the set of assumptions above, Find the seq number, ack number and the time

to send of each data segments if:

− The ACK of the second data segment is slow, taking 50 ms(instead of 30ms as

mentioned above).

− The first transmission of the 4th data segment is not received by the receiver.

− In the ACKs for the 8th data segment and subsequently, the receiver’s advertised

window is reset to 2 KB

Please fill in the value of time, seq number, and ack number for each segments A will

send.

Sending time

0

10

20

30

40

140

200

210

270

280

290

seq

0

1K

2K

3K

4K

4K

5K

6K

7K

8K

9K

ack

100

100

100

100

100

100

100

100

100

100

100 300

360

370

10K

11K

12K

100

100

100