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Chapter 11: Wide-Area Networks and the Internet

MULTIPLE CHOICE

1. MAN stands for:

a. Manchester Access Network c. Metropolitan-Area Network

b. Multiple-Area Network d. Multiple Access Network

ANS: C

2. Packet switching is based on:

a. store-and-forward c. real-time delivery

b. switched circuits d. all of the above

ANS: A

3. SNA stands for:

a. Standard Network Access c. Standard Network Architectureb. Small Network Access d. Systems Network Architecture

ANS: D

4. The number of layers in ISO OSI is:

a. 3 c. 7

b. 5 d. 8

ANS: C

5. The lowest-level layer in ISO OSI is called the:a. physical layer c. cable layer

b. link layer d. transport layer

ANS: A

6. Bad frames are usually detected by the:

a. frame layer c. error-check layerb. physical layer d. link layer

ANS: D

7. A virtual circuit is set up by the:

a. user c. network

b. link layer d. frame

ANS: C

8. Frame Relay:

a. is faster than X.25 c. allows for variable length packets

b. does less error checking than X.25 d. all of the above

ANS: D

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9. ATM stands for:a. Asynchronous Transfer Mode c. Asynchronous Transmission Model

b. Asynchronous Transmission Mode d. Automatic Test Mode

ANS: A

10. A bridge:a. separates a network into "collision domains"

b. looks at the address of each packet

c. operate at the data-link level

d. all of the above

ANS: D

11. IP stands for:

a. Internet Process c. Interconnect Protocol

b. Internet Protocol d. Interconnect Procedure

ANS: B

12. TCP stands for:

a. Transmission Control Process c. Transfer Connection Protocol

b. Transmission Control Protocol d. none of the above

ANS: B

13. Together, TCP/IP consists of:

a. 5 layers c. an application and a processb. 7 layers d. datagrams

ANS: A

14. IP is a:a. connection-oriented protocol c. connectionless protocol

b. virtual circuit d. non-robust protocol

ANS: C

15. The "lifetime" of a packet in an IP network:

a. is essentially forever

b. depends on elapsed time since transmission

c. depends on number of "hops" between nodesd. is approximately 200 milliseconds

ANS: C

16. UDP stands for:

a. User Datagram Protocol c. User Data Packet

b. User Data Protocol d. Universal Data Packet

ANS: A

17. HTTP stands for:

a. High-speed Transmission Test Procedure

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ANS: D

26. DNS stands for:

a. Domain Name Server c. Domain Numbering System

b. Domain Name System d. Domain Naming System

ANS: A

27. A DNS:

a. has become obsolete on the Internet

b. translates words to numbers

c. stores all domain addresses

d. describes the Internet address-naming procedure

ANS: B

28. An intranet connected to the Internet is often protected by:

a. a DNS c. a "firewall"

b. a "brick wall" d. the use of "spoofing" protocols

ANS: C

29. OSI stands for:

a. Open Systems Interconnection c. Open Systems Internet

b. Open Standard Interconnection d. none of the above

ANS: A

COMPLETION

1. A ____________________-Area Network would extend typically across a city.

ANS: Metropolitan

2. A ____________________-Area Network could extend across a nation.

ANS: Wide

3. A dedicated telephone line can be ____________________ on a monthly basis.

ANS: leased

4. The use of digital circuit-____________________ lines is cheaper than dedicated lines.

ANS: switched

5. Packet switching is done on a store-and-____________________ network.

ANS: forward

6. A ____________________ is a hierarchy of procedures for implementing digital communications.

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ANS: protocol

7. Voltage levels on a cable are specified at the ____________________ layer.

ANS: physical

8. Bad frames are usually detected at the ____________________ layer.

ANS: data-link

9. Setting up a path through the network is done by the ____________________ layer.

ANS: network

10. The X.25 protocol was developed by the ____________________.

ANS: CCITT

11. In X.25, the data-link layer is called the ____________________ layer.

ANS: frame

12. In X.25, the network layer is called the ____________________ layer.

ANS: packet

13. The physical route of a ____________________ circuit changes each time it is used.

ANS: virtual

14. Frame Relay requires channels with low ____________________ rates.

ANS: bit-error

15. Compared to X.25, Frame Relay does ____________________ error checking.

ANS: less

16. All ATM frames contain just ____________________ bytes.

ANS: 53

17. Small frame size and a high-speed channel allow ____________________-time communications.

ANS: real

18. ____________________ simply regenerate and retransmit packets in a network.

ANS: Repeaters

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19. ____________________ look at the address inside a packet to decide whether or not to retransmit it.

ANS: Bridges

20. ____________________ decide the best network path on which to forward a packet.

ANS: Routers

21. TCP/IP goes back to the ____________________ of the 1970s.

ANS:

ARPANET

DARPANET

22. Between ISO OSI and TCP/IP, ____________________ was used first.

ANS: TCP/IP

23. A ____________________ protocol does not track packets after they are sent.

ANS: connectionless

24. HTTP allows the use of ____________________ that jump to other pages on the web.

ANS: hyperlinks

25. The Internet "backbone" mostly uses high-speed ____________________ cables.

ANS: fiber-optic

26. A ____________________ translates words in an Internet address to numbers.

ANS: DNS

27. Intranets usually connect to the Internet through a ____________________ for security.

ANS: firewall

28. Voice over ____________________ is telephony done over the Internet.

ANS: IP

29. "____________________" is another term for real-time transmission over the Internet.

ANS: Streaming

30. Most people gain access to the Internet by subscribing to an ____________________.

ANS: ISP

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SHORT ANSWER

1. Name the three parts of an IP address as used on the Internet.

ANS:

Network number, Subnet number, Host number

2. Why is a logical channel called a "virtual" circuit?

ANS:

A logical channel is a way of keeping track of which two nodes on the network have messages for each

other. The actual physical path can change while packets are being sent. Virtual means it behaves like

direct circuit between 'A' and 'B', but it is not a direct circuit.

3. Why is it faster to send packets of a fixed size compared to packets of variable size?

ANS:

The processing required to store and forward packets of different lengths is greater than that required for

packets of a fixed length. More processing implies more time per packet, which implies fewer packets persecond through the network.

4. Why are the tasks involved in digital communications divided into layers in a protocol stack? Why not

just have one layer that does it all?

ANS:

Divide and conquer: it reduces complexity to a manageable job. One big layer could not be adapted to

newer media etc as easily as a system of independent layers. Think of subroutines in a computer program.

5. What is a "hop"?

ANS:Every time a packet is forwarded on to the next store-and-forward node in the network, it is considered to

be one "hop".

6. What does it mean to say a packet has a lifetime measured in hops?

ANS:

Each packet contains a number representing the maximum number of allowed hops. At each hop, this

number is reduced by one. When it gets to zero, the packet is deleted from the network.

7. Why should packets have a lifetime?

ANS:If they didn't, then the number of "lost" packets traveling around the network would continuously

increase. At some point, there would be no bandwidth left to carry real traffic.