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CSC 1113 – Introduction to Computers
LECTURE NOTES – CHAPTER 10
I. Understanding the Telephone System CIYF 10. Every student in your class is already familiar with POTS (Plain Old Telephone Service), which is defined as the public switched telephone network (PSTN). Take time in this section to explain briefly that this is for the most part an analog network, but is on the verge of becoming a truly digital network. Teaching Tip : This might be a good time to provide a clear definition and distinction between analog and digital. Web Link : Refer to the article “Can You Explain the Difference Between Analog and Digital Technology?” on the HowStuffWorks Web site (www.howstuffworks.com/question7.htm) for help in framing an explanation for your students.
A. Quality of Service
Ask students to reflect on their own experience with telephone service. Mention that we usually take it for granted that we can use the device in our home and reach any other telephone anywhere in the world in an instant with pretty good audio quality. This is known as quality of service (QoS).
B. Local Exchange Carriers (LECs)
Again, students are already familiar with the local exchange carriers (LECs ), also called telcos , and most often referred to as “the telephone company.” Mention that most home telephones in use today are analog and are linked to the carrier by means of copper wires called twisted-pair. Refer to Figure 10.3 as you describe twisted-pair wiring. From that point on, the local analog calls are routed to the local exchange switch using fiber-optic cables. Teaching Tip : If you have been accumulating items in your box of demonstration hardware, a length of twisted-pair wire, a length of fiber-optic cable, and a length of coaxial cable would be good additions to the box. Web Link : Encourage students to visit Fiber Optics Online (www.fiberopticsonline.com) for information about the fiber optics industry.
C. Long-Distance Transmission Media
Explain that the interexchange carrier (IXC) is the long-distance service that will transmit the call from your local exchange. Briefly mention the uses of copper wire, fiber optics , microwaves , and satellites in transmitting long distance calls.
D. Standards and Regulations
Briefly explain that the standards used for the public switched telephone network are governed by the International Telecommunications Union (ITU) , which is a division of the United Nations. Web Link : To learn more about the ITW and international telecommunications standards, encourage students to visit the ITU home page at www.itu.int.
Chapter 10 Lecture Notes Explain that the concept of universal service is based on the belief in the United States that telephone service is vital to public safety and economic welfare. Mention that universal service is not an issue in other countries where telephone service is a state- run monopoly. Class Exercise : Prior to discussing universal service in class, suggest that each student read the Impacts section “Universal Service: No More Access for Everyone?” What if the concept of universal service was extended from voice communications to include all communications? Would it make sense to have Internet service universally accessible to every American?
E. More Ways to Access the System
Ask students to recall that most phones are analog devices connected to the local loop’s twisted-pair wiring. Discuss the fact that there are alternative ways to gain access to telephone services, such as private branch exchanges (PBX) , wireless (cellular) phones , and leased lines. Briefly define each of these alternative methods of access.
F. The PSTN in Perspective
Summarize the fact that the PSTN forces computer users to transform digital data into analog form; therefore it is of limited use for data communications. Discuss the last mile problem and possible solutions. Classroom Exercise : Encourage students to ponder other possible solutions to the last mile problem. Could wireless connections provide a nifty solution? II. Modems: From Digital to Analog and Back CIYF 10. Explain that as long as the telephone company is using analog equipment in the local loop, all data and voice messages must be sent in analog form.
A. How Modems Work
Define a modem as a device that, first, transforms digital signals into analog tones (a process called modulation ) that can be carried through the telephone system, and second, handles the transformation of analog tones on the receiving end into digital signals (a process called demodulation ). Refer to Figure 10.10 to assist in the explanation.
B. Asynchronous Communication
Define asynchronous communication as the method of sending one data bit at a time in a series. Define synchronous communication as the opposite of asynchronous. Web Link : Refer to the Webopedia definition of “synchronous” (http://www.webopedia.com/TERM/s/synchronous.html) for a diagram explaining synchronous communication.
C. Modulation Protocols
Explain that, as in all communications between devices, a set of standards or protocols is required. Define the components of a protocol, including the data transfer rate and baud rate. Briefly explain the modulation protocols V.90 and V..
Chapter 10 Lecture Notes
B. Cable Modems
Explain that a cable modem is designed to operate over cable TV lines. Mention that the coaxial cable used by cable TV provides much greater bandwidth than telephone lines, so a cable modem can be used to achieve extremely fast access to the World Wide Web. This, combined with the fact that millions of homes are already wired for cable TV, has made the cable modem something of a holy grail for Internet and cable TV companies.
C. Electrical Power Systems
Explain that with this type of alternative access, data communications can be sent over electrical power lines with speeds comparable to DSL and cable modems. Although this approach is not readily compatible with the U.S. power grid, it is expected to attract users in Asia and Europe. Classroom Exercise : Ask students to read the Currents section “The Bright Future of Bluetooth™.” Most major companies have embraced the concept of Bluetooth technology. Lead students in a discussion to debate the statement in the textbook, “One thing is for sure: Bluetooth will soon change the way our devices communicate.” This will be especially interesting to the class if you have Bluetooth-enabled devices to demonstrate the technology. V. Convergence: Is It a Phone or a Computer? CIYF 10. Begin this section by defining the terms digitization (the transformation of media into digital systems) and convergence (the morphing of technology into interesting hybrids).
A. The Everything PC
Web Link : Encourage students to check out the Cassius (www.cassiuspc.com/boat/), an all-in-one entertainment center and personal computer for use on a boat.
B. TV Internet Set-Tops
Web Link : Direct students to the site www.accessdevices.co.uk/ for an interactive demonstration on Internet TV.
C. Personal Communications Service (PCS)
Personal Communication Services bundle voice communications, numeric and text messaging, voice-mail, and various other features into one device, service contract, and bill. PCS is carried over cellular links, most often digital.
D. Internet Telephony
Web Link : Direct students to iptel.org (www.iptel.org/info/) for more information on Internet telephony.
E. Internet Faxing
Web Link : Direct students to IntelliFax.com (www.intellifax.com/) for more information on Internet faxing.
Chapter 10 Lecture Notes VI. CHAPTER REVIEW CIYF 10. Web Link : Refer students to www.prenhall.com/ciyf2004 for a review of the chapter, to answer the questions, and to complete the exercises and Web research questions. Takeaway Points: Ask students to recall the objectives identified at the beginning of this lesson. Tie the initial objectives with the essential lecture points that met the objectives Objective : Explain the limitations of the public switched telephone network (PSTN) for sending and receiving computer data. The public switched telephone network (PSTN) is predominantly digital, except for the local loop, which uses low-bandwidth twisted-pair wire connected to analog telephones. Objective : Discuss how modems transform digital computer signals into the analog tones suited for the telephone system. To send digital data over the telephone system, it’s necessary to modulate the signal (transform it into analog form). On the receiving end, the signal must be demodulated (transformed back into digital form). Modems (modulators/demodulators) perform this service. Objective : Define bandwidth and discuss the bandwidth needs of typical users. The term bandwidth refers to the data transfer capacity of a communications channel and is measured in bits per second (bps). Modulation protocols are standards that define how modems work. The latest protocol is called V.90, and it enables data transfer rates of up to 56 Kbps. 56 Kbps isn’t sufficient for real-time videoconferencing or other advanced multimedia applications. For these applications, bandwidths of 1 Mbps or more are needed for good quality. Objective : List two digital telephony standards that can bring digital connections into homes and offices using existing wiring. ISDN and ADSL are two digital telephony services that can bring digital service directly to homes and offices using twisted-pair wiring. Basic ISDN services can provide data transfer rates of up to 128 Kbps; ADSL provides 1 Mbps or more. Objective : Provide examples of how convergence is blurring the boundaries among popular communication devices, including phones, computers, and TVs. Digitization is blurring the boundaries between phones, computers, and TVs. MSN^ TV brings Internet capabilities to TV viewing, and PCS enables high-bandwidth data communications through cellular telephones. Objective : Discuss the prospects for telephony through the Internet. In Internet telephony, voice is routed over the public Internet or private networks constructed using Internet standards. However, these networks can’t guarantee PSTN’s quality of service.
