Chapter 6 Computer Networks
By 黄永平，权勇，孙永雄，王智，丰小月，孙铭会 Knowledge point:
6.1. OSI model
6.2. TCP/IP protocol
6.3. three types of networks
6.4. connecting devices
6.5. client-server model
Multiple-Choice Questions:
18. A is a set of rules that controls the interaction of different devices in a network or internetwork. (6.2)
a. model
b. protocol
c. dialog
d. synchronization point
19. The OSI model has layers.(6.1)
a. five
b. six
c.seven
d. any of the above
20. The layer of the OSI model organizes bits into logical data units called frames. (6.1)
a. physical
b. data-link
c. network
d. transport
21. The layer of the OSI model enables a person to access the network. (6.1)
a. data-link
b. transport
c. application
d. physical
22. The layer of the OSI model compresses and decompresses data. (6.1)
a. physical
b. data-link
c. session
d. presentation
23. The layer of the OSI model encrypts data. (6.1)
a. physical
b. data-link
c. session
d. presentation
24. The layer of the OSI model transmits a bit stream over a physical medium. (6.1)
a. physical
b. data-link
c. network
d. transport
25. The layer of the OSI model is responsible for node-to-node delivery of a frame between two adjacent stations. (6.1)
a. transport
b. network
c. data-link
d. session
26. The layer of the OSI model is responsible for source-to-destination delivery of the entire message. (6.1)
a. transport
b. network
c. data-link
d. session
27. The layer of the OSI model is responsible for source-to-destination delivery of an individual packet. (6.1)
a. transport
b. network
c. data-link
d. session
28. The layer of the OSI model controls the dialog between users. (6.1)
a. transport
b. session
c. presentation
d. application
29. Through the layer of the OSI model, mail services and directory services are available to network users. (6.1)
a. data connection
b. session
c. transport
d. application
30. Cindy’s Dessert Heaven is a bakery with four outlets in San Francisco. The outlets need to communicate with each other. This type of network is probably a . (6.3)
a. LAN
b. MAN
c. WAN
d. none of the above
31. Kate’s Irish Potato Company is based in Ireland but has branches in Boston and San Francisco. The branches communicate with each other through a . (6.3)
a. LAN
b. MAN
c. WAN
d. none of the above
32. Vecchiarelli Consultants occupies two adjacent rooms in the CofflandBuilding. The network, consisting of four workstations and a printer, is probably a . (6.3)
a. LAN
b. MAN
c. WAN
d. none of the above
33. What is the domain name in the email address kayla@pit.arc.nasa.gov? (6.2)
a. kayla
b. pit.arc.nasa.gov
c. kayla@pit.arc.nasa.gov
d. nasa.gov
34. Which topology uses a hub or switch? (6.3)
a. bus
b. ring
c. star
d. all of the above
35. Which topology needs cable terminators? (6.3)
a. bus
b. ring
c. star
d. all of the above
36. A is a connecting device that only regenerates the signal. (6.4)
a. repeater
b. bridge
c. router
d. gateway
37. A is a connecting device that acts as a protocol converter. (6.4)
a. repeater
b. bridge
c. router
d. gateway
38. A is a connecting device that segments traffic. (6.4)
a. repeater
b. bridge
c. router
d. gateway
39. A is a device that can route a packet based on its network layer address. (6.4)
a. bridge
b. router
c. repeater
d. all of the above
40. A bridge operates at of the OSI model. (6.4)
a. the first layer
b. the first two layers
c. the first three layers
d. all layers
41. A gateway operates at of the OSI model. (6.4)
a. the first layer
b. the first two layers
c. the first three layers
d. all layers
42.The layer of TCP/IP has functions similar to those of the application, presentation, and session layers of the OSI model. (6.2)
a. transport
b. network
c. application
d. session
43. The IP address is currently bits in length. (6.2)
a. 4
b. 8
c. 32
d. any of the above
44. The transport layer protocol of TCP/IP is called . (6.2)
a. TCP
b. UDP
c. IP
d. a and b
45. is a protocol for file transfer. (6.2)
a. FTP
b. SMTP
c. TELNET
d. HTTP
46. is a protocol for mail services. (6.2)
a. FTP
b. SMTP
c. TELNET
d. HTTP
47. is a protocol for accessing and transferring documents on the WWW. (6.2)
a. FTP
b. SMTP
c. TELNET
d. HTTP
48. A document has fixed contents. (6.5)
a. static
b. dynamic
c. active
d. all of the above
Review questions:
2. Name the layers of the OSI model? (6.1)
Answer: Physical layer, Data link layer, Network layer, Transport layer, Session layer, Presentation layer and Application layer.
3. Name the layers of the TCP/IP protocol suite. (6.2)
Answer: The layers of the TCP/IP protocol suite are: physical and data-link layers network layer, transport layer, and application layer.
8. What are the three common topologies in LANs? Which is the most popular today? (6.3)
Answer: bus topology, star topology, ring topology, star topology
9. Name four types of network connecting devices. (6.4)
Answer: the four types of network connecting devices are repeater, bridge, router and gateway.
Exercises:
49. Which of the OSI layers is(are) involved in each of the following activities: (6.1)
a)sending a frame to the next station
answer: Data-Link
b)sending a packet from the source to the destination
answer: Network
c)sending a long message from the source to the destination
answer: Transport
d)logging into a remote computer
answer: Application
e)encrypting and decrypting data
answer: Presentation
f)changing the data from the machine code to Unicode
answer: Presentation
50. A small part of a bus LAN with 200 stations is damaged. How many stations are affected by this damage? (6.3)
Answer:
In bus topology, when a station sends a frame to another computer, all computers receive the frame and check its destination address. So no computer is affected by this damage.
52. A small part of a ring LAN with 200 stations is damaged. How many stations are affected by this damage? (6.3)
Answer:
In the ring topology, a computer sends a frame to another computer by sending it to its neighbor. So, all the stations are affected by this damage.
55. An engineer notices that the data received by computer at the two ends of a bus LAN contain many errors. What do you think is the problem? What can be done to solve the problem? (6.3)
Answer:
Maybe the cable terminators do not work properly. Repair or change the invalid cable terminators.
60 Change the following IP address from binary notation to dotted-decimal notation:
01111110 01100000 0111000 01111111 (6.2)
Answer: 126.96.112.127
61. Explain the client-server model on the Internet. In which layer of the TCP/IP protocol suite is the model implemented? (6.5)
Answer:
In this model, a client, an application program running on a local machine, requests a service from a server, an application program running on a remote machine. Usually, the server program is always running, and the client program runs only when needed. The model is implemented in the application layer of the TCP/IP protocol suite.
65. A user uses a browser to download a game. What type of document is downloaded? (6.2)
Answer:
The game needs to be run at the browser site. So type of document is active documents.
67. Write a URL that uses HTTP. It accesses a file with the path /user/general in a computer with the alias name www.hadb. (6.2)
Answer:
The URL uses HTTP. The alias name is www.hadb. The path is /user/general. So the URL is HTTP:// www.hadb/user/general.
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