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Chapter Overview Modems The Internet and Web Browsers

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Modem Basics A modem allows computers to communicate

over telephone lines by modulating and demodulating signals.

Integrated Services Digital Network (ISDN) uses a terminal adapter (TA) for high-speed digital connections.

You should understand the following terms: Baud rate Bits per second (bps) IP address

Transmission Control Protocol/Internet Protocol (TCP/IP)

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Communication

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Digital Communication Asynchronous communication does not

use a common data clock. Synchronous communication uses the

system clock at timed intervals.

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How Communication Protocols Work

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Hardware Internal modems Universal serial bus (USB) modems External analog modems

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ISDN Terminal Adapters ISDN is an all-digital phone connection

that carries voice and high-speed data transmissions.

ISDN uses a TA instead of a modem. TAs are difficult to install.

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The RS-232 Port The Electronic Industries Association

(EIA) developed the RS-232 standard for low-speed data communication.

The RS-232 cable uses either a 25-pin or 9-pin connector.

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Telephone-Line Basics for Modems Half-duplex uses RJ-11 and has two

wires, so it can send or receive only one signal at a time.

Full-duplex uses RJ-12 and has four wires, so it can simultaneously send and receive.

Multifunction modems can send faxes and handle voice mail.

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Modem Installation Installing an internal modem expansion

card requires you to check settings, install the board and drivers, and set up the command set.

Installing an external modem requires you to connect to a COM port, plug in the cabling, and configure the software.

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Modem Speeds Modem speed is measured in baud rate

and bps. Baud rate is the number of voltage or

frequency changes per second. Bps is the actual number of bits that are

transmitted per baud cycle. CCITT (Comité Consultatif International

Télégraphique et Téléphonique) sets modem speed standards.

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Fax Speeds Groups 1 and 2 pertain to slower analog

devices. Group 3 is for digital equipment. Group 4 allows the highest resolution of

output.

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Information Transfer Protocols American Standard Code for Information

Interchange (ASCII) is an old protocol that uses the standard ASCII character set.

Kermit was an early synchronous protocol that is rarely used today.

Xmodem transfers data in 128-byte blocks and uses parity error checking.

Ymodem transfers data in 1024-byte blocks. Zmodem adds new features: crash recovery,

automatic downloading, and streaming file transfer.

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Handshaking Handshaking negotiates the

communication rules between modems. Modems on both ends must agree on

the rules. Modems can handle flow control

through hardware or software. Hardware flow control is faster and

more dependable.

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Modem Standards Modem standards include error detection

and data compression standards. Manufacturers and standards committees

develop communication standards. Bell Telephone developed early modem

standards 103 and 212A. CCITT modem standards are commonly

known as Vdot standards. The V.90 standard has replaced K56flex

and x2 as the 56-Kbps modem standard.

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Modem Commands The Hayes AT command set is an

unofficial standard. Commands can be used for

troubleshooting. The computer must be in terminal mode

to use these commands.

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Troubleshooting

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Troubleshooting (Cont.)

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The Internet The Internet is a worldwide network that

uses TCP/IP. The World Wide Web (WWW) is a subset

of the Internet. Web sites are hosted by computers that

house the content. A browser is client software designed to

access the WWW.

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Electronic Mail E-mail requires the following:

E-mail server User account on that server Client program to send and receive e-mail Account information

You can configure a client program to automatically download e-mail.

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Internet Protocols and Services File Transfer Protocol (FTP) is used to transfer files. TCP/IP is the standard suite of protocols used on

the Internet. Each host on an IP network requires a unique 32-

bit binary address. Internet Service Providers (ISPs) provide the

connection between dial-up users and the Internet. Domain Name System (DNS) identifies domain

names on the Internet. A DNS server matches DNS names to IP addresses.

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Getting Connected Different types of connections require

different hardware and support. A firewall between a computer and the

Internet provides security. ISPs provide services and connections. A browser allows you to access and

view Web pages.

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Using the PING Command

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Chapter Summary Modems convert parallel digital data to and from

serial analog data. Modems can be installed internally or externally. Modem speeds are measured in bps. AT commands are used to manually

communicate with and test a modem. The Internet provides information and services

that are made available through browsers. The Internet uses DNS and TCP/IP to route traffic. The PING command can be used to troubleshoot

IP networks.