Bài giảng Computer - Chapter 15

Chapter Overview ModemsThe Internet and Web Browsers 1Modem 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 addressTransmission Control Protocol/Internet Protocol (TCP/IP)2Communication 3Digital Communication Asynchronous communication does not use a common data clock.Synchronous communication uses the system clock at timed intervals. 4How Communication Protocols Work 5Hardware Internal modemsUniversal serial bus (USB) modemsExternal analog modems 6ISDN 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. 7The 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. 8Telephone-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. 9Modem 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. 10Modem 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. 11Fax Speeds Groups 1 and 2 pertain to slower analog devices.Group 3 is for digital equipment.Group 4 allows the highest resolution of output. 12Information 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. 13Handshaking 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. 14Modem 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. 15Modem 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. 16Troubleshooting 17Troubleshooting (Cont.) 18The 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. 19Electronic Mail E-mail requires the following: E-mail server User account on that serverClient program to send and receive e-mailAccount information You can configure a client program to automatically download e-mail. 20Internet 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. 21Getting 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. 22Using the PING Command 23Chapter 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. 24