Chapter Overview

1
Chapter Overview

• Modems
• The Internet and Web Browsers

2
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)

3
Communication
4
Digital Communication

• Asynchronous communication does not use a common
  data clock.
  
• Synchronous communication uses the system clock
  at timed intervals.

5
How Communication Protocols Work
6
Hardware

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

7
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.

8
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.

9
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.

10
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.

11
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.

12
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.

13
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.

14
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.

15
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.

16
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.

17
Troubleshooting
18
Troubleshooting (Cont.)
19
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.

20
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.

21
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.

22
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.

23
Using the PING Command
24
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.