121.计算机网络A.试卷

宁波大学2012 / 2013 学年第1 学期考试卷（A）班级：__________ 学号: __________姓名: __________课号：101G09HA 课名：计算机网络(答题卡和每页试卷均请写上姓名学号，答案请填在答题卡上)阅卷教师: _____________ 成绩: _______________

I.Choose the single correct answer from following choose. (1.5*20=30)

[Correct checked:1.5; Other wise:0]

[ ]1.If you want to find the mail server of the domain https://www.360docs.net/doc/b94333229.html,，select the DNS search : A．Type=A

B．Type=CName

C．Type=NS

D．Type=MX

[ ]2.UDP socket identified by:

A．two-tuple (source IP address, source port number)

B．two-tuple (dest. IP address, dest. port number)

C．two-tuple (source IP address, dest. IP address)

D．two-tuple (source port number, dest. port number)

[ ]3.Download a web page with multiple objects, which is the most efficient way？

A．None persistent HTTP without pipeline

B．None persistent HTTP with pipeline

C．Persistent HTTP without pipeline

D．Persistent HTTP with pipeline

[ ]4.Got CIDR IP address 200.23.16.0/24, how many subnet can be allocated with wask 255.255.255.128?

A．2

B．4

C．8

D．l6

[ ]5.Which of the following protocols does Ethernet use now?

A．Pure ALOHA

B．Slotted ALOHA

C．CSMA/CD

D．CDMA

[ ]6.Which protocol allows host to dynamically obtain its IP address from network?

A. DHCP

B. NA T

C. DCT

D. DNS

[ ]7.In Client-server paradigm, process sends/receives messages to/from :

A．Slot

B．Socket

C．Port

D．Passive [ ]8.Which Aplication protocol use separate control and data connections on port:

A．Email on 110 and 25

B．Ftp on 21 and 20

C．Http on 80 and 8080

D．Telnet on 25 and 1025

[ ]9. Which can provide protection against broadcast storms:

A. Routers

B. Bridges

C. Switchs

D. Hubs

[ ]10.Virtual circuits is a signaling protocols that is used in:

A．ATM, frame-relay, X.25

B．today’s Internet

C．wireless network

D．VPN

[ ]11.If no free buffers in router, the arriving packets will be:

A．dropped

B．queued

C．returned

D．forward

[ ]12.Which can provides delay measurement from source to router along end-end Internet path towards destination：

A．Ping

B．Traceroute

C．Ipconfig

D．Nslookup

[ ]13. Which of the following measures the time from one segment transmission to ACK receipt：A．sample RTT

B．estimation RTT

C．simple RTT

D．establish RTT

[ ]14. Single shared broadcast channel can not be used for multiple access by:

A．Channel Partitioning

B．Random Access

C．Taking turns

D．point-to-point protocol

[ ]15. In which network, propagation delay may be greater then queuing delay:

A．Fiber Network

B．Wire LAN

C．Satellite Network

D．WIFI Network

[ ]16.In GBN,when receiver receive a out-of-order packet,then discard and re-ACK with: A．highest in-order sequence #

B．lowest in-order sequence #

C．highest out-of-order sequence #

D．lowest out-of-order sequence #

[ ]17. Large IP datagram divided (fragmented) within network, it will be reassembled: A．only at last switch

B．only at final destination

C．only at next router

D．only at last router

[ ]18.What is not the Key Network-Layer Functions:

A．forwarding

B．routing

C．connection setup

D．flow control

[ ]19.Which is an Inter-AS routing protocols:

A．RIP: Routing Information Protocol

B．BGP: Border Gateway Protocol

C．IGRP: Interior Gateway Routing Protocol

D．ICMP: Interior Control Message Protocol

[ ]20.In RDT Approachs, which is designed for bit error:

A．checksum

B．pipeline

C．sequence #

D．ACK or NAK

II.Choose the multiple correct answer from following choose. (2*10=20)

[All correct checked:2; Part correct checked:1; No checked:0; Full checked:0]

1. How data transferred through internet?

[ ]A.circuit switching

[ ]B.power switching

[ ]C.packet switching

[ ]D.direct-connected 2.Each layer takes data from above, then

[ ]A.adds header information to create new data unit

[ ]B.adds header information to update old data unit

[ ]C.passes new data unit to layer below

[ ]D.delivery PDU back to above

https://www.360docs.net/doc/b94333229.html,er Agent implements user interface & application-level protocol, such as:

[ ]A.Web: browser

[ ]B.E-mail: mail reader

[ ]C.FTP: cuteftp

[ ]D.DNS: proxy

4.We can visit mail service by those protocols:

[ ]A.POP3

[ ]B.FTP

[ ]C.IMAP

[ ]D.HTTP

5.In decentralized directory of P2P, the disadvantages of approach maybe:

[ ]https://www.360docs.net/doc/b94333229.html,plex protocol

[ ]B.bootstrap node needed

[ ]C.single point of failure

[ ]D.group leaders can get overloaded

6.Which services are not available in UDP:

[ ]A.delay guarantees

[ ]B.end to end transport

[ ]C.bandwidth guarantees

[ ]D.congestion control

7.InTCP reliable data transfer, Retransmissions are triggered by:

[ ]A. timeout events

[ ]B. duplicate ACKs

[ ]C. duplicate data

[ ]D. slow start

8.These are those status in TCP sender :

[ ]A. Data received from application

[ ]B. Ack received

[ ]C. Timeout

[ ]D. Delay Ack

9.Implementation NAT router must:

[ ]A.replace (source IP address, port #) of outgoing datagram to

(NA T IP address, new port #)

[ ]B.replace (source IP address, port #) of outgoing datagram to

(source IP address, NAT port #)

[ ]C.remember in NAT translation table for translation pair(IP address, port #)

[ ]D.replace destination fields of incoming datagram with corresponding

(source IP address, port #) stored in NAT table early

10. In the MAC Protocols, there are those broad classes:

[ ]A.Channel Partitioning

[ ]B.Random Access

[ ]C.Freedom Access

[ ]D.Taking turns

III.Fill the blank from options. (1.5*16=24)

1).What services might a network application need from a transport protocol? We can broadly

classify an application's service requirements along three dimensions:[1?], [2?] and [3?].

(options:

secret / data loss / delay / bandwidth / orders / timing )

2). The key fields in the IPv4 datagram head are the following:[4?] , [5?] , [6?] , [7?] , [8?] and [9?].

(options:

Port number / Header Length / Datagram Length / Identifier / ACK / SEQ / Protocol / Source IP Address / Destination IP Address)

3).Please fill the general format of mail message:

(options:

Content-Type / From / To / Accept-language / Subject / Method / MIME-Version / User-agent / Content-Transfer-Encoding / Cr Lf / Status Code) IV.Question (26)

1. In this scenario, host A sends two segments back to back. The first segment has sequence number 92

and 8 bytes of data, and the second segment has sequence number 100 and 20 bytes of data. Suppose that both segments arrive intact at B, and B sends two separate acknowledgements for each of these segments.

The first of these acknowledgements has acknowledgment number 100; the second has acknowledgment number 120. Suppose now that neither of the acknowledgements arrive at host A before the timeout of the first segment. When the timer expires, host A resends the first segment with sequence number 92.

Question 1:Does A also resend second segment that has sequence number 100?（3）

Question 2:Why？（可以使用英文或中文回答。）（5）

2.In this scenario, suppose host A sends the two segments, exactly as in the second example. The

acknowledgment of the first segment is lost in the network, but just before the timeout of the first segment, host A receives an acknowledgment with acknowledgment number 120.

Question 3:Does A resend second segment that has sequence number 92?（3）

Question 4:Does A resend second segment that has sequence number 100?（3）

Question 5:Why？（可以使用英文或中文回答。）（5）

Question 6:How does Delayed-ACK work in TCP receiver action？（可以使用英文或中文回答。）（7）(所有答案请填在答题卡上，答在试卷上的答案一律无效)