Chapter Overview • Modems • The Internet and Web Browsers
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)
Digital Communication • Asynchronous communication does not use a common data clock. • Synchronous communication uses the system clock at timed intervals.
Hardware • Internal modems • Universal serial bus (USB) modems • External analog modems
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.