Apply Your Knowledge

Exercises

7.1. Investigating WAN Options

Estimated time: 30 minutes

Because you are unlikely to have the equipment or facilities to create your own WAN, this exercise requires that you investigate the WAN options that would be available to you if you were to create a WAN from your location to another.

Your research should include visiting the Web site of a local telecommunications provider and ascertaining the options open to you. Given that financial considerations are generally a major factor in a decision such as this, you should look at the lower-cost options such as cable, DSL, or ISDN in preference to leased-line circuits, such as T1 lines. From your research you should be able to answer the following questions:

  • Which services are available in your location?

  • Which services offer the best value for the money, based on available bandwidth, cost of installation, ongoing costs (line/equipment rental), maintenance, and call charges, if applicable?

  • Which of the available services would you choose, and what would the estimated annual cost be for that service?

Although you should not sign up for any of the services during the course of this exercise, through this exercise you will gain valuable information because this is exactly the kind of project you are likely to be assigned when working in a real-world situation as an administrator. Evaluation and recommendation of products is an important element of a network administrator's role.

Exam Questions

1:Your company currently use a standard PSTN communication link to transfer files between LANs. Until now, the transfer speeds have been sufficient for the amount of data that needs to be transferred. Recently, a new application has been purchased that requires a minimum transmission speed of 1.5Mbps. You have been given the task of finding the most cost-effective solution to accommodate the new application. Which of the following technologies would you use?

  1. T3

  2. X.25

  3. T1

  4. BRI ISDN

A1: c. A T1 line has a transmission capability of 1.544Mbps and is considerably cheaper than a T3 line. X.25 and BRI ISDN cannot provide the required transmission speed. For more information, see the “WAN Technologies” section in this chapter.
2:Which of the following terms is used to describe a station on an FDDI network that is attached to both rings?

  1. DUS

  2. SAS

  3. DAS

  4. DRS

A2: c. DAS describes a device that occupies both rings on an FDDI network. None of the other answers are valid. For more information, see the “WAN Technologies” section in this chapter.
3:Which of the following statements are true of ISDN? (Choose the two best answers.)

  1. BRI ISDN uses 2B+1D channels.

  2. BRI ISDN uses 23B+1D channels.

  3. PRI ISDN uses 2B+1 D channels.

  4. PRI ISDN uses 23B+1D channels.

A3: a, d. BRI ISDN uses 2B+1D channels, which are two 64Kbps data channels, and PRI-ISDN uses 23B+1D channels. The other answers are not valid. For more information, see the “WAN Technologies” section in this chapter.
4:You have been hired to establish a WAN connection between two offices—one in Vancouver and one in Seattle. The transmission speed can be no less than 2Mbps. Which of the following technologies could you choose?

  1. T1

  2. PSTN

  3. T3

  4. ISDN

A4: c. The only technology in this question that is capable of transfer speeds above 2Mbps is a T3 line. None of the other technologies listed can provide the transmission speed required. For more information, see the “WAN Technologies” section in this chapter.
5:A customer calls you and wants information on FDDI. Which of the following are true of FDDI? (Choose the two best answers.)

  1. DASs are linked to both rings on FDDI.

  2. SASs are linked to both rings on FDDI.

  3. FDDI uses fiber-based media.

  4. FDDI uses copper-based media.

A5: a, c. DASs in an FDDI network connect to both rings, creating a fault-tolerant measure for the Class A device. FDDI is implemented over a fiber-based media. Answer b is incorrect because an SAS is connected to only one ring. Answer d is incorrect because FDDI can be implemented only over fiber-optic cable. For more information, see the “WAN Technologies” section in this chapter.
6:Which if the following technologies use exclusively fiber-based media? (Choose the two best answers.)

  1. FDDI

  2. T1

  3. SONET

  4. ISDN

A6: a, c. FDDI is implemented as two counter-rotating rings using fiber-based media. SONET is a fiber-based standard that was developed by Bell Communications Research, following the AT&T breakup in 1984. T1 and ISDN can both be implemented over copper-based cable. For more information, see the “WAN Technologies” section in this chapter.
7:Due to recent cutbacks, your boss approaches you, demanding an alternative to the company's costly dedicated T1 line. Only very small amounts of data will require transfer over the line. Which of the following are you likely to recommend?

  1. ISDN

  2. FDDI

  3. The PSTN

  4. X.25

A7: c. When very little traffic will be sent over a line, the PSTN is the most cost-effective solution, although it is limited to 56Kbps. All the other WAN connectivity methods accommodate large amounts of data and are expensive in comparison to the PSTN. For more information, see the “WAN Technologies” section in this chapter.
8:Which of the following technologies requires a logical connection between the sending and receiving devices?

  1. Circuit switching

  2. Virtual-circuit packet switching

  3. Message switching

  4. High-density circuit switching

A8: b. When virtual circuit switching is used, a logical connection is established between the source and the destination device. None of the other answers are valid. For more information, see the “Introduction to WAN Technologies” section in this chapter.
9:Which of the following technologies requires dial-up access? (Choose the two best answers.)

  1. FDDI

  2. ISDN

  3. Packet switching

  4. The PSTN

A9: b, d. Both the PSTN and ISDN require dial-up connections to establish communication sessions. The other answers are not valid. For more information, see the “WAN Technologies” section in this chapter.
10:Which of the following is an advantage of ISDN over the PSTN?

  1. ISDN is more reliable.

  2. ISDN is cheaper.

  3. ISDN is faster.

  4. ISDN uses 53Kbps fixed-length packets.

A10: c. One clear advantage that ISDN has over the PSTN is its speed. ISDN can combine 64Kbps channels for faster transmission speeds than the PSTN can provide. ISDN is no more or less reliable than the PSTN. ISDN is more expensive than the PSTN. Answer d describes ATM. For more information, see the “WAN Technologies” section in this chapter.
11:Which of the following best describes the process of creating a dedicated circuit between two communication endpoints and directing traffic between those two points?

  1. Multiplexing

  2. Directional addressing

  3. Addressing

  4. Circuit switching

A11: d. Circuit switching is the process of creating a dedicated circuit between two communication endpoints and directing traffic between those two points. None of the other answers are valid types of switching. For more information, see the “Introduction to WAN Technologies” section in this chapter.
12:Which of the following technologies uses fixed-length packets, or cells, that are 53 bytes in length?

  1. ATM

  2. ISDN

  3. VPN

  4. FDDI

A12: a. ATM uses fixed packets, or cells, with lengths of 53 bytes—48 bytes for data information and 5 bytes for the header. None of the other technologies listed use this cell format. For more information, see the “WAN Technologies” section in this chapter.
13:You need to implement a low-cost WAN implementation. Which of the following are considered public networks? (Choose the two best answers.)

  1. ATM

  2. The Internet

  3. FDDI

  4. The PSTN

A13: b, d. The Internet and the PSTN are considered public networks and are therefore the most cost-effective data transmission solutions. ATM and FDDI are examples of private networking technologies. For more information, see the “Introduction to WAN Technologies” section in this chapter.
14:Which of the following switching methods is associated with the store-and-forward technique?

  1. Packet switching

  2. Message switching

  3. Circuit switching

  4. Virtual-circuit packet switching

A14: b. Message switching uses a store-and-forward switching method. This method is impractical for real-time data transmissions but well suited for other applications, such as email. None of the other switching methods are associated with store-and-forward. For more information, see the “Introduction to WAN Technologies” section in this chapter.
15:Which of the following are packet-switching technologies? (Choose the two best answers.)

  1. ATM

  2. X.25

  3. FDDI

  4. Frame Relay

A15: b, d. X.25 and Frame Relay are both packet-switching technologies. ATM and FDDI are not considered packet-switching technologies. For more information, see the “WAN Technologies” section in this chapter.
16:Which of the following are disadvantages of a public network?

  1. Security

  2. Accessibility

  3. Availability

  4. Cost

A16: a. There are many advantages of a public network, but security is a concern because data transmissions can be intercepted. All the other answers are advantages of using a public network. For more information, see the “Introduction to WAN Technologies” section in this chapter.
17:Which of the following circuit-switching strategies are used by ATM? (Choose the two best answers.)

  1. SVC

  2. VCD

  3. PVC

  4. PCV

A17: a, c. ATM uses two types of circuit switching—PVC and SVC. VCD and PCV are not the names of switching methods. For more information, see the “WAN Technologies” section in this chapter.
18:On an ISDN connection, what is the purpose of the D channel?

  1. It carries the data signals.

  2. It carries signaling information.

  3. It allows multiple channels to be combined, to provide greater bandwidth.

  4. It provides a temporary overflow capacity for the other channels.

A18: b. The D channel on an ISDN link carries signaling information, whereas the B, or bearer, channels carry the data. The other answers are not valid. For more information, see the “WAN Technologies” section in this chapter.
19:Which of the following technologies uses a PAD?

  1. ISDN

  2. ATM

  3. X.25

  4. OC-3

A19: c. A PAD is associated with X.25 networks. None of the other technologies listed use PADs. For more information, see the “WAN Technologies” section in this chapter.
20:Of the following technologies, which are limited to 56Kbps? (Choose the two best answers.)

  1. Modem

  2. ISDN

  3. X.25

  4. Frame Relay

A20: a, c. Both modem links and X.25 are limited to 56Kbps. ISDN and Frame Relay are both capable of greater speeds than either X.25 or modems. For more information, see the “WAN Technologies” section in this chapter.
Suggested Readings and Resources

1. Habraken, Joe . Absolute Beginner's Guide to Networking, third edition. Que Publishing, 2001.

2. Shinder, Debra Littlejohn . Computer Networking Essentials. Cisco Press, 2001.

3. McCarty, Ronald W . Cisco WAN Quick Start. Cisco Press, 2000.

4. Cisco Systems Inc. Internetworking Troubleshooting Handbook, second edition. Cisco Press, 2001.

5. Marcus, Scott J . Designing Wide Area Networks and Internetworks: A Practical Guide. Addison-Wesley, 1999.

6. Frame Relay and associated WAN information, www.mywanonline.com/fr_online_learning.htm.

7. WAN technology information from Cisco, www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/introwan.htm.

8. General WAN info and links, www.techfest.com/networking/wan.htm.

9. Computer Networking Tutorials and Advice, compnetworking.about.com.

10. “TechEncyclopedia,” www.techencyclopedia.com.

11. Networking technology information from Cisco, www.cisco.com/public/products_tech.shtml.

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