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 Describe digital modem architecture for high-speed communications through IDSN, cable, DSL, and satellites Guide to Operating Systems, Third Edition

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 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 Components: data pump, controller, and UART Data pump component that performs modulation/demodulation Guide to Operating Systems, Third Edition

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 (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 (continued) Data terminal equipment (DTE) data transfer rate Guide to Operating Systems, Third Edition

Analog Modem Hardware Basics (continued) Guide to Operating Systems, Third Edition

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 (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 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) Host Signal Processor (HSP) modems dispense with the controller and data pump hardware entirely Guide to Operating Systems, Third Edition

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 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) Guide to Operating Systems, Third Edition

Hayes AT Command Set for Analog Modems (continued) Guide to Operating Systems, Third Edition

Digital Modems Digital modems Telecommunications networks: 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

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) 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 (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 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) Data Over Cable Service interface Specifications (DOCSIS) DOCSIS 1.0 DOCSIS 1.1 DOCSIS 2.0 Guide to Operating Systems, Third Edition

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) Guide to Operating Systems, Third Edition

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 (continued) Guide to Operating Systems, Third Edition

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 (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 (continued) Guide to Operating Systems, Third Edition

Satellite Available 500 Kbps for downloading speeds more and more rural areas metropolitan areas 500 Kbps for downloading speeds 50 Kbps for uploading Guide to Operating Systems, Third Edition

Satellite Guide to Operating Systems, Third Edition

Data Communications Techniques Flow control way to halt and resume the flow of data Guide to Operating Systems, Third Edition

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 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) Guide to Operating Systems, Third Edition

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 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) 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 (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 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) 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 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 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 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) Minicom create a modem configuration – see Figure 7-8 Guide to Operating Systems, Third Edition

Configuring Dial-up Connections in UNIX/Linux (continued) Guide to Operating Systems, Third Edition

Configuring Dial-up Connections in UNIX/Linux (continued) 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 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) 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 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) Guide to Operating Systems, Third Edition

Configuring Modems in Mac OS X (continued) Guide to Operating Systems, Third Edition

Summary 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) See Table 7-4 for a review of analog and digital remote access speeds Guide to Operating Systems, Third Edition

Summary (continued) Guide to Operating Systems, Third Edition