1 / 31

Chapter 8

Chapter 8. Data Transmission and Modems. Agenda. Circuit Mode of transmission Digital transmission Analog transmission for digital signals - modems Methods Classification Interfaces Functions Selection Criteria. Circuit. Signal rate

oshin
Download Presentation

Chapter 8

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Chapter 8 Data Transmission and Modems

  2. Agenda • Circuit • Mode of transmission • Digital transmission • Analog transmission for digital signals - modems • Methods • Classification • Interfaces • Functions • Selection Criteria

  3. Circuit • Signal rate • No. of signal changes (amplitude, frequency, or phase) on a circuit per second • Baud • Types: dibits, tribits, and quadbits • Speed • No. of bits that a circuit can carry in 1 second • Bits per second (bps) used for measurement

  4. Mode of Transmission • Data flow • Physical connection • Timing

  5. Data Flow - US • Simplex transmission • Television and radio • Half-duplex (HDX) transmission • CB radio, terminal • Full-duplex (FDX) transmission • Telephone, computer to computer

  6. Physical Connection • Parallel transmission • Fast • Simple • Line cost • Serial transmission • Complicated transmitter and receive • Decomposing and reconstructing

  7. Timing • Asynchronous transmission • Start/stop bits for character synchronization • Mark (1or stop) /space (0 or start ) bits for bit synchronization • Simple, inexpensive, slow speed transmission • For personal computer • Synchronous transmission • Clock circuitry • One to four synchronization characters for each block of data • Large amount of data on dedicated line

  8. Digital Signals • Unipolar (positive voltage for 1, no voltage for 0) • Bipolar, nonreturn-to zero (NRZ) • Manchester coding (low-to-high is 1, high-to- low is 0) • Differential Manchester (no transition at the beginning of the bit period is 1, second transition at the beginning of the bit period is 0) • Benefits: self-clocking, and error detection • Bipolar, return-to-zero

  9. Benefits of Digital Transmission • Better data integrity (detect & correct error) • Higher capacity cables (fiber-optic) • Easier integration (voice, data, video, etc.) • Better security and privacy (encrypt data) • Lower cost (large-scale integrated circuitry)

  10. Digital Transmission of Analog Signals • Quantization • Quantizing noise or digitizing distortion • Codec (coder/decoder): analog-to-digital (A/D) converter & digital-to-analog (D/A) converter • Methods • Pulse code modulation (256 integers, 8000 per second) • Adaptive differential pulse code modulation (difference) • Delta modulation (1 for +, 0 for -)

  11. Digital Transmission of Digital Signals • Digital transmitter/receiver (data service unit/channel service unit (DSU/CSU)) • Simpler & cheaper • Transmitter for shaping & timing the signal, interface between DTE and line • Receiver for protection of excessive voltage, diagnostic and testing

  12. Analog Transmission of Digital signals (Modems – I) • Modulation and Demodulation • Receiver (modulation), control unit (auto dial & auto answer), transmitter (demodulation), & power supply • Equalizer in transmitter & adaptive equalizer in receiver (adjust to fit the characteristics of the telephone line) • Methods • Frequency shift keying (FSK) • Phase shift keying (PSK): 180 degree (1 bit), 90 degree (2 bits), 45 degree (3 bits) • Differential phase shift keying (DPSK) • Quadrature amplitude modulation (QAM): combination of 8 phases & 4 relative amplitudes

  13. Modems - II • Methods • Trellis code modulation: signal processor, error correction for error free transmission, high speed • Standards by ITU-T • V.32 for 9.6 kbps & V.32bis for 14.4 kbps • V.34 for 28.8 kbps & V.34+ or V.34bis for 33.6 kbps • V.90 for 56 kbps

  14. Modems - III • Handshaking • Exchange signals between modems • Test the characteristics of circuit and quality • determine baud rate, modulation technique and error control • Data compression • V.42bis by ITU-T • Microcom Networking Protocol (MNP 7 or 10) by Microcom, Inc.

  15. Modem Classification • Simplex, half-duplex, full-duplex transmission modems • Asynchronous or synchronous transmission modems • Acoustically coupled modems (portable) • Limited distance modems/short haul modems (less than 20 miles) • Modem eliminators/null modems (cable less than several thousand feet)

  16. Modem Classification - II • Facsimile modems • Error correction and data compression • Modem for fiber-optics circuits • Digital-electrical to digital-optical • Cable modems • DTE to cable television system cable • Data Over Cable Service Interface Specification (DOCSIS) by CableLabs • For large files and not logon process

  17. Modem Classification - III • Reverse channel • Slow speed reverse channel for signaling one another • Auto dial/auto answer • Hayes Microcomputer Product, Inc. • Command AT for attention • Internet service provider usage • Dial-backup public telephone network connection for leased telephone line • Internal modem • Single circuit card • No switch to change the parameters and operations

  18. Modem Interfaces • Between modem and line • Between DTE and modem

  19. Between Modem and Line • Two- to four-wire cable • RJ-11 plug

  20. Between Modem and DTE • RS-232-C interface • V.24 interface • RS-232-D interface • RS-449 interface • RS-336 interface • X.21 interface • X.21bis interface • Current loop interface

  21. RS-232-C Interface • By EIA and ITU-T V.24 • Characteristics • 25-pin connector at both end • digital and serial • Female for DCE and male for DTE • Pins 2 and 3 to pass data, other for signaling • Limitations • 50 -100 feet cable length • 2,400 - 9,600 bps • Hard to difference 0 and 1 when speed is high and cable is long

  22. RS-232-D Interface • Specifications for the 25-pin connector • Addition of a shield on the cable • Redefinition of protective ground and some pins

  23. RS-449 Interface • 37 pins • 4,000 feet cable • Not well accepted

  24. RS-336 Interface • Automatic dialing from computer to remote terminals for data collection • Not for high speed transmission

  25. X. Interfaces • X.21 interface • Digital connection to a digital public telephone network • X.21bis interface • Terminal to packet switch network via analog line

  26. Current Loop Interface • Represent 1 and 0 by presence or absence of an electrical current • Simple and inexpensive • Nonstandard • Teletywriter system

  27. Other Modem Functions • Reverse channel for signal one another to determine the speed • Auto dial/auto answer • Modem diagnostics • Loop back for accuracy checking

  28. Modem Selection Criteria • Digital or analog signals • Asynchronous or synchronous • Speed • Distance • Type of line • Cost • Functions

  29. Spread Spectrum • Analog signal for analog or digital data • Frequency hopping ad direct sequence • Generated by Pseudo random number generator

  30. Points to Remember • Circuit • Mode of transmission • Digital transmission • Analog transmission for digital signals - modems • Methods • Classification • Interfaces • Functions • Selection Criteria

  31. Discussion • Design the data transmission and modem specification for a bank

More Related