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Modems and Other Communications Devices. Guide to Operating Systems Third Edition. Objectives. After reading this chapter and completing the exercises you will be able to: Explain analog modem architecture Use the classic Hayes AT modem command set with computer communications applications

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Modems and other communications devices

Modems and Other Communications Devices

Guide to Operating Systems

Third Edition


Objectives
Objectives

After reading this chapter and completing the exercises you will be able to:

  • Explain analog modem architecture

  • Use the classic Hayes AT modem command set with computer communications applications

  • Describe digital modem architecture for high-speed communications through IDSN, cable, DSL, and satellites

Guide to Operating Systems, Third Edition


Objectives continued
Objectives (continued)

After reading this chapter and completing the exercises you will be able to:

  • Explain the basics of telephone-line data communications

  • Configure modem and internet communications in different operating systems

Guide to Operating Systems, Third Edition


Analog modem architecture
Analog Modem Architecture

  • Modem

    • hardware and software that connects two incompatible systems

  • Plain old telephone service (POTS) lines – old term

  • Public switched telephone network (PSTN) lines - modern term

Guide to Operating Systems, Third Edition


Analog modem hardware basics
Analog Modem Hardware Basics

  • Components:

    • data pump, controller, and UART

  • Data pump

    • component that performs modulation/demodulation

Guide to Operating Systems, Third Edition


Analog modem hardware basics continued
Analog Modem Hardware Basics (continued)

  • Controller

    • provides the modem’s identity

    • interprets Attention (AT) commands

  • Protocol

    • specifies how networked data is formatted

    • how it is transmitted

    • how it is interpreted at the receiving end

Guide to Operating Systems, Third Edition


Analog modem hardware basics continued1
Analog Modem Hardware Basics (continued)

  • International Telecommunications Union (ITU)

    • establishes modem protocol standards

    • compose the ITU-T standards

  • Latest standards define a 56 Kbps to 64 Kbps protocol

Guide to Operating Systems, Third Edition


Analog modem hardware basics continued2
Analog Modem Hardware Basics (continued)

  • Data terminal equipment (DTE)

    • data transfer rate

Guide to Operating Systems, Third Edition


Analog modem hardware basics continued3
Analog Modem Hardware Basics (continued)

Guide to Operating Systems, Third Edition


Analog modem hardware basics continued4
Analog Modem Hardware Basics (continued)

  • Modem is called the data communications equipment (DCE)

  • Speed is the DCE communications rate

  • UART

    • electronic chip

    • the Universal Asynchronous Receiver-Transmitter

    • converts data from the computer

Guide to Operating Systems, Third Edition


Analog modem hardware basics continued5
Analog Modem Hardware Basics (continued)

  • Asynchronous communication

    • most common method for today’s desktop computers

    • uses fairly accurate clocks (timers) at both ends of the connection to synchronize data

  • Synchronous communication

    • sends information in blocks (frames) of data that include embedded clock signals

Guide to Operating Systems, Third Edition


Software based modems
Software-Based Modems

  • Winmodems

    • software-based modems

    • controllerless modem that retains a hardware data pump (Digital Signal Processor (DSP)

    • implements the controller functions in software

Guide to Operating Systems, Third Edition


Software based modems continued
Software-Based Modems (continued)

  • Host Signal Processor (HSP) modems

    • dispense with the controller and data pump hardware entirely

Guide to Operating Systems, Third Edition


Software based modems continued1
Software-Based Modems (continued)

  • Disadvantage

    • software takes up memory and processor cycles

  • Advantage

    • their dependence on particular operating systems

    • cost savings and upgradeability

Guide to Operating Systems, Third Edition


Hayes at command set for analog modems
Hayes AT Command Set for Analog Modems

  • Hayes command or Attention (AT) commands

    • created by Dennis Hayes

    • begin with the letters AT

    • tells the modem to interpret the next character string as a command

Guide to Operating Systems, Third Edition


Hayes at command set for analog modems continued
Hayes AT Command Set for Analog Modems (continued)

Guide to Operating Systems, Third Edition


Hayes at command set for analog modems continued1
Hayes AT Command Set for Analog Modems (continued)

Guide to Operating Systems, Third Edition


Digital modems
Digital Modems

  • Digital modems

    • digital devices that use digital transmission media

    • network or serial devices

    • connect via Point-to-Point (PPP)

  • Telecommunications networks:

    • ISDN

    • Cable networks

    • DSL

    • Satellite

Guide to Operating Systems, Third Edition


Modems and other communications devices
ISDN

  • Integrated Services Digital Network (ISDN)

    • uses standard copper telephone line pair

    • digital equipment on either end of the connection

    • ISDN router to route the transmission to the right place

    • terminal adapter (TA), a type of digital modem

Guide to Operating Systems, Third Edition


Isdn continued
ISDN (continued)

  • Basic rate interface (BRI)

    • aggregate data rate of 144 Kbps

    • three channels

  • Primary rate interface (PRI)

    • supports faster data rates

    • aggregate bandwidth equal to 1.544 Mbps

Guide to Operating Systems, Third Edition


Isdn continued1
ISDN (continued)

  • PRI

    • used for LAN-to-LAN connectivity

    • ISP sites

    • videoconferencing

    • corporate sites that support telecommuters

Guide to Operating Systems, Third Edition


Cable modems
Cable Modems

  • Cable modem

    • used to attach to cable data services

    • external device

    • plugs into a USB port or network interface card

    • connected to the coaxial cable used for the cable TV system

Guide to Operating Systems, Third Edition


Cable modems continued
Cable Modems (continued)

  • Data Over Cable Service interface Specifications (DOCSIS)

    • DOCSIS 1.0

    • DOCSIS 1.1

    • DOCSIS 2.0

Guide to Operating Systems, Third Edition


Dsl modems
DSL Modems

  • Digital Subscriber Line (DSL)

    • high-speed digital data communications service

    • challenging ISDN and cable modems

    • digital technology that works over copper wire

    • must install an intelligent adapter in your computer

Guide to Operating Systems, Third Edition


Dsl modems continued
DSL Modems (continued)

Guide to Operating Systems, Third Edition


Dsl modems continued1
DSL Modems (continued)

  • Dedicated to a single user

  • Employs the full bandwidth

  • Connected by means of a combined DSL adapter and router

  • Router

    • device that can be used to direct network traffic and create a firewall

Guide to Operating Systems, Third Edition


Dsl modems continued2
DSL Modems (continued)

Guide to Operating Systems, Third Edition


Dsl modems continued3
DSL Modems (continued)

  • DSL services:

    • Asymmetric Digital Subscriber Line (ADSL)

    • G.lite Asymmetric Digital Subscriber Line (G.lite ADSL)

    • Integrated Services Digital Network Digital Subscriber Line (IDSL)

    • Rate Adaptive Digital Subscriber Line (RADSL)

    • High Bit-Rate Digital Subscriber Line (HDSL)

Guide to Operating Systems, Third Edition


Dsl modems continued4
DSL Modems (continued)

  • DSL services (continued):

    • Symmetric high Bit-Rate Digital Subscriber Line (SHDSL)

    • Very High Bit-Rate Digital Subscriber Line (VDSL)

    • Symmetric Digital Subscriber Line (SDSL)

  • ADSL is the most commonly used version of DSL

Guide to Operating Systems, Third Edition


Dsl modems continued5
DSL Modems (continued)

Guide to Operating Systems, Third Edition


Satellite
Satellite

  • Available

    • more and more rural areas

    • metropolitan areas

  • 500 Kbps for downloading speeds

  • 50 Kbps for uploading

Guide to Operating Systems, Third Edition


Satellite1
Satellite

Guide to Operating Systems, Third Edition


Data communications techniques
Data Communications Techniques

  • Flow control

    • way to halt and resume the flow of data

Guide to Operating Systems, Third Edition


Software flow control
Software Flow Control

  • Xon-Xoff

    • uses Ctrl+S character (ASCII 19) to stop the flow of data (Xoff)

    • Ctrl+Q (ASCII 17) to resume (Xon)

Guide to Operating Systems, Third Edition


Hardware flow control
Hardware Flow Control

  • Halts and resumes the movement of data

    • changing the voltage on specific pins in the serial interface

    • eliminates the problem of the modem confusing data with control signals

Guide to Operating Systems, Third Edition


Hardware flow control continued
Hardware Flow Control (continued)

Guide to Operating Systems, Third Edition


Error correction
Error Correction

  • Possible errors

    • a bit can be lost

    • an extraneous bit can be introduced

    • a bit can be flipped

Guide to Operating Systems, Third Edition


Error correction1
Error Correction

  • Basic error correction

    • start and stop bits

    • each eight-bit byte is framed by a start bit and a stop bit

Guide to Operating Systems, Third Edition


Error correction continued
Error Correction (continued)

  • Parity checking

    • data verification process

    • ensures data integrity

    • system of data bit comparisons between the sending and receiving computer

Guide to Operating Systems, Third Edition


Error correction continued1
Error Correction (continued)

  • Link Access Protocol for Modems (LAPM)

    • used to construct data into discrete frame-like units for transmission over communications lines

Guide to Operating Systems, Third Edition


Data compression
Data Compression

  • Modems compress data sent

  • Data compression routine for a picture with a lot of blue

    • the “compressed” representation of the screen shows a blue dot and a number that represents the number of times the blue dot is repeated

    • does it “on the fly,” compressing the data while you send it

Guide to Operating Systems, Third Edition


Data compression continued
Data Compression (continued)

  • Lempel-Ziv-Welch (LZW) compression method

    • compresses data as it is sent

    • can detect when the data is already compressed

Guide to Operating Systems, Third Edition


Modems and the operating system
Modems and the Operating System

  • Available in all operating systems

  • Installation CD-ROMs shipped with most all modems

Guide to Operating Systems, Third Edition


Configuring dial up connections in windows 2000 xp server 2003
Configuring Dial-up Connections in Windows 2000/XP/Server 2003

  • See page 352 for setup information on Windows 2000, Windows XP, and Windows Server 2003

Guide to Operating Systems, Third Edition


Configuring dial up connections in unix linux
Configuring Dial-up Connections in UNIX/Linux 2003

  • Two purposes

    • dial-in device

    • dial-out device

  • For dial-in connectivity, UNIX uses a daemon

    • an internal, automatically running program called getty

Guide to Operating Systems, Third Edition


Configuring dial up connections in unix linux continued
Configuring Dial-up Connections in UNIX/Linux (continued) 2003

  • Minicom

    • create a modem configuration – see Figure 7-8

Guide to Operating Systems, Third Edition


Configuring dial up connections in unix linux continued1
Configuring Dial-up Connections in UNIX/Linux (continued) 2003

Guide to Operating Systems, Third Edition


Configuring dial up connections in unix linux continued2
Configuring Dial-up Connections in UNIX/Linux (continued) 2003

  • UUCP

    • UNIX to UNIX Copy Protocol

    • found on almost all UNIX versions

Guide to Operating Systems, Third Edition


Configuring modems and scripts in netware 6 x
Configuring Modems and Scripts in NetWare 6.x 2003

  • Components for Novell Internet Access Server

    • WMDMMGR.EXE

    • MOEDMMGR.DLL

    • Modem configuration files

    • A sample PPP login script

Guide to Operating Systems, Third Edition


Configuring modems and scripts in netware 6 x continued
Configuring Modems and Scripts in NetWare 6.x (continued) 2003

  • See page 357-358

    • recommended steps for modifying a modem configuration file or PPP login script

Guide to Operating Systems, Third Edition


Configuring modems in mac os x
Configuring Modems in Mac OS X 2003

  • Provide information to configure the device

    • telephone number for the ISP

    • user name for the ISP account

    • password for the ISP account

Guide to Operating Systems, Third Edition


Configuring modems in mac os x continued
Configuring Modems in Mac OS X (continued) 2003

Guide to Operating Systems, Third Edition


Configuring modems in mac os x continued1
Configuring Modems in Mac OS X (continued) 2003

Guide to Operating Systems, Third Edition


Summary
Summary 2003

  • Modems open WAN communications

  • Most PCs have a built-in analog modem

  • Analog modem architecture

  • Hayes AT modem command set

  • Digital versus analog modems

Guide to Operating Systems, Third Edition


Summary continued
Summary (continued) 2003

  • See Table 7-4 for a review of analog and digital remote access speeds

Guide to Operating Systems, Third Edition


Summary continued1
Summary (continued) 2003

Guide to Operating Systems, Third Edition