Section 7.1 Explain how modems function Describe how satellites transmit data Identify the role of a multiplexer Explain how synchronous and asynchronous communications work Section 7.2 Explain different computer numbering systems Demonstrate how to convert numerical values between decimal, binary, and hexadecimal systems

Section 7.3 Describe different transmission technologies that can run on POTS Explain how various digital transmission technologies work

pp Communications Guide to Reading Main Ideas Modems are one of the most common ways for computers to connect to each other. Satellite systems are used to connect WANs across the globe. Multiplexers are a key component of WAN technology. Transmissions can be asynchronous or synchronous. Key Terms V series AT command set PC Card standards cable modem geostationary earth orbit (GEO) medium-earth orbit (MEO) low-earth orbit (LEO) asynchronous synchronous frame

pp Communications Modems The term modem comes from the two primary tasks it performs: modulation and demodulation. In many ways, a modem is like a language translator between the analog and digital components.

pp Communications Modems Modems have several sets of standards: V series Hayes-compatible (AT command set) PC Cards V series Standards that cover today’s modems, with speeds up to 56 Kbps. (p. 197) Hayes-Compatible Standards The set of transmission signals, commands, used originally by Hayes modems for exchanging status information, such as readiness to send or receive. (p. 197) PC Card standards Standards developed for personal computer cards and intended for laptop users that target a broad range of devices, including modems. (p. 197)

pp Communications Modems Developments in the past few decades enabled modem speeds to transmit at 56 Kbps. However, the 56K transmissions can occur downstream. The upstream, or outgoing transmission from the modem, is limited to 45 Kbps.

pp Communications Modems There are several different types of modems available: Cable modems ISDN modems DSL modems cable modem A modem that uses a cable television connection to get transmission rates that are faster than a dial-up connection. (p. 201)

pp Communications Satellite Systems Large WANs use satellites to transfer data. Satellites orbit the Earth in three tiers: Geostationary earth orbit (GEO) Medium-earth orbit (MEO) Low-earth orbit (LEO) geostationary earth orbit (GEO) The orbit in which satellites fly at 22,000 miles above the earth in fixed positions. (p. 200) medium-earth orbit (MEO) The orbit in which satellites fly between 6,250 and 12,500 miles above Earth. (p. 200) low-earth orbit (LEO) The orbit in which satellites fly between 310 and 1,240 miles above Earth. (p. 200)

pp Communications Multiplexers Multiplexers and demultiplexers are used to combine and break the high rate data stream. Multiplexing can be achieved through: Frequency Division Multiplexing (FDU) Time Division Multiplexing (TDM) Statistical Time Division Multiplexing (STDM) Wavelength Division Multiplexing (WDU)

pp Communications Transmission Types There are two basic types of transmission types: Asynchronous Synchronous asynchronous communication A form of data transmission that involves a delay of seconds, minutes, or even days. Communication does not happen instantly. (p. 201) synchronous communication Communication whose bits are sent and received in a timed method. Digital systems and networks rely on this method that results in faster transmissions, but it is also more complex and more expensive. (p. 202)

pp Communications Transmission Types In asynchronous transmissions, the “building blocks” are bytes delineated by start and stop bits. In synchronous transmissions, the “building blocks” are based on frames: blocks of bits separated by equal time intervals.

pp Communications You Try It Activity 7A – Installing an Internal Modem (p. 198)

pp Data-Encoding Basics Guide to Reading Main Ideas Computers use numerical values to transmit data. Computers understand only binary numbers. Hexadecimal is a numbering system that simplifies complex binary numbers. Decimal is a numbering system people use. Key Terms decimal base 10 binary base 2 bit hexadecimal base 16 American Standard Code for Information Interchange (ASCII) Extended Binary Coded Decimal Interchange Code (EBCDIC) Unicode

27 XXVII ||||| ||||| ||||| ||||| ||||| || pp Data-Encoding Basics Numbering Systems To fully understand computers and how data are transmitted between computers, you need to understand a few things about numbering systems. There are many different methods for representing numerical data. For example, the following shows different ways to represent the concept of “27.”

pp Data-Encoding Basics Numbering Systems The system you have used since you learned how to count is the decimal system. The decimal system is based on the use of ten digits. This is base ten. decimal A number system based on the use of ten digits (0, 1, 2, 3, 4, 5, 6, 7, 8, and 9). (p. 204) base 10 The number of digits that forms the base of the system. Digits from left to right in a decimal number represents a power of ten. (p. 204)

pp Data-Encoding Basics Numbering Systems The most important system for computers is the binary system, called base 2. It is critical for computers, which only understand two digits or bits. binary A system of numbers based on two digits, 1 and 0. In computers, the number 0 represents an off electrical state and the number 1 is on. (p. 205) base 2 The binary system uses only two digits, 1 and 0, which is why it is called base 2. (p. 205) bit A binary digit and is the smallest amount of data used by a computer. (p. 205)

pp Data-Encoding Basics Numbering Systems This table lists decimal and binary values.

pp Data-Encoding Basics Numbering Systems Binary digits are difficult to read and are often simplified into hexadecimal or base 16. Hexadecimal is often used in HTML documents to represent color values. hexadecimal A number system based on 16 characters, including the numerals 0 to 9 and the letters A to F. (p. 207)

pp Data-Encoding Basics Text Representation In addition to the numerical systems of base 2, 10, and 16, there are several text- representation systems used by computers. ASCII EBDIC Unicode American Standard Code for Information Interchange (ASCII) One of the oldest, and most commonly used codes. In this system, each letter, character, or nonprinting character is given a specific numerical code. (p. 208) Extended Binary Coded Decimal Interchange Code (EBCDIC) Code that was developed for use on IBM computers. EBCDIC values were assigned for easy use with punch cards. (p. 208) Unicode Code that was developed to combat limitations of systems like the ASCII system. (p. 208)

pp Data-Encoding Basics You Try It Activity 7B – Converting Decimal Numbers to Binary Numbers (p. 206) Activity 7C – Converting Binary to Hexadecimal (p. 207)

pp Communication Carriers Guide to Reading Main Ideas Telecommunications are an essential part of WAN technology. Some types of transmissions use POTS lines to transmit data at various speeds. Digital communications travel over a variety of media and at a range of high speeds. Key Terms Plain Old Telephone Service (POTS) Public Switched Telephone Network (PSTN) digital data service (DDS) Basic Rate Interface (BRI) Primary Rate Interface (PRI) fractional T1 Digital Subscriber Line (xDSL)

pp Communication Carriers POTS Telecommunication systems are set along two paths, analog and digital. The most common analog communication uses Plain Old Telephone Service (POTS) provided by the phone company. Plain Old Telephone Service (POTS) One of the largest and most used networks. Also known as the phone system. (p. 211)

pp Communication Carriers POTS POTS is provided by the Public Switched Telephone Network (PSTN). For networking, it can be in two forms: Dial-up Leased times Public Switched Telephone Network (PSTN) A communication service known as the public telephone system. (p. 211)

pp Communication Carriers POTS Dial-up networking works well for individuals needing remote access to a network. Types of dial-up connections include: SLIP CSLIP PPP PPTP PPPoE

pp Communication Carriers POTS Leased lines are permanent dial-up lines dedicated to full- time data transfer use. Leased lines are often described as direct connections that are not routed through the phone company’s switching system.

pp Communication Carriers Digital Digital connections allow for faster speed to access the networks. There are several options for digital communication: Digital data service (DDS) ISDN T1/T3 Digital Subscriber Line (xDSL) digital data service (DDS) Communication lines that are dedicated, point-to-point connections. Lines transmit digital data, rather than voice calls. (p. 213) Digital Subscriber Line (xDSL) A family of digital communications technologies. These services provide high-speed network access over the standard copper wires run into homes and offices by the telephone company. (p. 215)

pp Communication Carriers Digital ISDN is available in two different forms: Basic Rate Interface (BRI) Primary Rate Interface (PRI) Basic Rate Interface (BRI) A form of ISDN that is typical in home use. There are two B (bearer) channels that carry data at the rate of 64 Kbps. (p. 214) Primary Rate Interface (PRI) A form of ISDN that is generally used to connect a company’s telephone network. The line is divided into many channels. (p. 214)

pp Communication Carriers Digital T1/T3 lines transmit in full duplex, meaning both sides of the transmission can send and receive simultaneously. To save on the cost of a full T1 line, businesses can opt for a fractional T1. fractional T1 Part rather than all of the T1 bandwidth. A business often leases this type of bandwidth. (p. 215)

pp Communication Carriers Digital xDSL provides high speed access over standard copper wires. This range is limited, however, as shown in the table below.

Chapter 7 Resources For more resources on this chapter, go to the Introduction to Networks and Networking Web site at