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Transmission of Digital DATA : Interfaces and Modems

Transmission of Digital DATA : Interfaces and Modems. Prof. Choong Seon HONG. 6 장 Transmission of Digital Data: Interfaces and MODEMs. 6.1 Digital Data Transmission 6.2 DTE-DCE Interface 6.3 Other Interface Standards 6.4 모뎀 (MODEM). 6.1 Digital Data Transmission.

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Transmission of Digital DATA : Interfaces and Modems

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  1. Transmission of Digital DATA :Interfaces and Modems Prof. Choong Seon HONG

  2. 6장Transmission of Digital Data: Interfaces and MODEMs 6.1 Digital Data Transmission 6.2 DTE-DCE Interface 6.3 Other Interface Standards 6.4모뎀(MODEM)

  3. 6.1 Digital Data Transmission • Primary concern when considering the transmission of data from one device to another is the wiring

  4. Digital Data Transmission(cont’d) • Parallel Transmission • By grouping, we can send data n bits at a time instead of one • 장점 : 속도(speed) • 단점 : 고가(expansive) 전송거리(short distance): 최대25 feets

  5. Digital Data Transmission(cont’d) • Parallel transmission

  6. Digital Data Transmission(cont’d) • Serial Transmission • one bit follows another • 장점 : 단일 channel, 저가 • 단점 : require interface converter

  7. Digital Data Transmission(cont’d) • Serial Transmission

  8. Digital Data Transmission(cont’d) • 비동기 전송(Asynchronous Transmission) • send one start bit(0) at the beginning and one or more stop bits(1) at the end of each byte • ex) the connection of a terminal to a computer • 장점 : cheap and effective

  9. Digital Data Transmission • 동기전송(synchronous transmission) • Sending bits one after another without start/stop bits or gaps. It is the responsibility of the receiver to group the bits • The receiver counts the bits as they arrive and groups them in eight-bit units • 장점 : 속도(speed)

  10. 6.2 DTE-DCE Interface • DTE(Data Terminal equipment) : 데이터 단말장치 • DCE(Data Circuit-terminating Equipment) : 데이터 회선 종단 장치

  11. DTE-DCE Interface(cont’d) • DTE(Data Terminal Equipment) ~ is any device that is a source of destination for binary digital data • terminal • Personal computer • printer • fax machine and so on

  12. DTE-DCE Interface(cont’d) • DCE (Data Circuit-Terminating Equipment) ~ is any device (functional unit) that transmits or receives data in the form of an analog or digital signal through a network • Modulator/demodulator

  13. DTE-DCE Interface(cont’d) • 표준안(Standards) • defining the connection between a DTE and DCE

  14. DTE-DCE Interface(cont’d) • Standards • EIA (Electronic Industries Association) • EIA-232 • EIA-442 • EIA-449 • ITU-T (International Telecommunications Union-Telecommunications Sector) • V series (전화망에 관한 데이터 통신) • X series (데이터 통신망에 대한 데이터통신)

  15. DTE-DCE Interface(cont’d) • EIA-232(RS-232) • defining the mechanical, electrical and functional characteristics • 기계적인 규격 (mechanical specification) • defining the interface as a 25-wire cable with a male (plug) and a female (receptacle) DB-25 pin connector • length may not exceed 15m(50 feet) • 전자적인 규격 (electrical specification) • define voltage levels and the type of signal(예: NRZ-L)

  16. DTE-DCE Interface(cont’d) • Sending the data • To be recognized as data, the amplitude of a signal must fall between 3 and 15 volts or between –3 and –15 volts

  17. DTE-DCE Interface(cont’d) • Control and Timing • Only 4 wires out of 25 available in an EIA-232 interface are used for data functions • Signals must be sent using OFF less than –3 volts and ON greater than +3 volts

  18. DTE-DCE Interface(cont’d) • 기능 규격(Functional Specification)

  19. DTE-DCE Interface(cont’d) • Functions of Pins in EIA-232, DB-9

  20. DTE-DCE Interface(cont’d) • 예: synchronous full-duplex transmission Step1 :preparation Step2 : Readiness Step3 : Set up Step1 :preparation Step2 : Readiness Step3 : Set up

  21. DTE-DCE Interface(cont’d) Step4: Data Transfer Step 5 : Clearing Step4:Data Transfer Step 5 : Clearing

  22. DTE-DCE Interface(cont’d) • Null Modem • not needed to connect two compatible digital devices directly Ex) connecting two DTEs in the same building • Using regular data pin connections with and without DCEs

  23. DTE-DCE Interface(cont’d) • Crossing Connections • Null modem pin connection

  24. 6.3 Other Interface Standards • needs more speed and/or distance • EIA-449 • EIA-530 • X.21

  25. Other Interface Standards(cont’d) • EIA-449 • DB-37 pin • DB-9 pin • DB-37 and DB-9 connections

  26. Other Interface Standards(cont’d) • Pin Functions • category I pins ~ are compatible with those of EIA-232 • category II pins ~ have no equivalent in EIA-232

  27. Pin Functions Category Pin Functions Category 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 Shield Signal rate indicator Unassigned Send data Send timing Receive data Request to send Receive timing Clear to send Local loopback Data mode Terminal ready Receive ready Remote loopback Incoming call Select frequency Terminal timing Test mode Signal ground I I I I I I II I I I II II I II Receive Common Unassigned Send data Send timing Receive data Request to send Receive timing Clear to send Terminal in service Data mode Terminal ready Receive ready Select ready Signal quality New signal Terminal timing Standby indicator Send common II I I I I I I I II I I I II II I II II Other Interface Standards (cont’d) • DB-37 pins

  28. Other Interface Standards(cont’d) • DB-9 pins Pin Function EIA-232 Equivalent 1 2 3 4 5 6 7 8 9 Shield Secondary receive ready Secondary send data Secondary receive data Signal ground Receive common Secondary request to send Secondary clear to send Send common 1 14 16 7 12 19 13

  29. Other Interface Standards(cont’d) • Electrical specification : RS-423 and RS-422 • EIA-449 uses two other standards to define its electrical specification • RS-423 (unbalanced circuits) • RS-422 (balanced circuits)

  30. Other Interface Standards(cont’d) • RS-423 : Unbalanced Mode

  31. Other Interface Standards(cont’d) • RS-422 : Balanced Mode

  32. Other Interface Standards(cont’d) • Canceling of noise in balanced mode

  33. Other Interface Standards(cont’d) • EIA-530 • is a new version of EIA-449 that uses DB-25 pins

  34. Other Interface Standards(cont’d) • X.21 ~ is an interface designed by the ITU-T to address many of the problems existing in the EIA • eliminating most of the control circuits of the EIA standards • DB-15 connector • Byte timing (pins 7 and 14) : byte synchronization • Control and indication • Pin 3 : equivalent of request to send (control) • Pin 5 : equivalent of clear to send (indication)

  35. Other Interface Standards • DB-15 pins Pin Function Pin Function Transmit data or control Control Receive data or control Indication Signal element timing Byte timing Reserved 1 2 3 4 5 6 7 8 Shield Transmit data or control Control Receive data or control Indication Signal element timing Bye timing Signal ground 9 10 11 12 13 14 15

  36. 6.4 MODEMs • The most familiar type of DCE

  37. MODEMs(cont’d) • MODEM • stands for modulator/demodulator • Modulator : converts a digital signal to an analog signal • using the digital-to-analog mechanism of ASK, FSK, PSK, and QAM • Demodulator : converts an analog signal to a digital signal

  38. MODEMs(cont’d) • Transmission Rate • Bandwidth • Each line has an upper limit and a lower limit on the frequencies of the signals it can carry. This limited range is called the bandwidth

  39. MODEMs(cont’d) • Telephone line bandwidth • A telephone line has bandwidth of almost 3000 Hz

  40. MODEMs(cont’d) • Modem speed • The bandwidth required for ASK transmission is equal to baud rate of signal • in half-duplex ASK, because the effective bandwidth of a telephone line is 2400Hz, the maximum bit rate is also 2400.

  41. MODEMs(cont’d) • Baud rate in full-duplex ASK • Although ASK has a good bit rate, it is not used today because of noise

  42. MODEMs(cont’d) • FSK(Frequency Shift Keying) • Baud rate in half-duplex FSK • Baud rate in full-duplex FSK • Max baud rate = Max bit rate = [2400 – (fc1 – fc0)]/2

  43. MODEMs(cont’d) • Baud Rate in Full-Duplex FSK

  44. MODEMs(cont’d) • PSK and QAM(비교) Theoretical bit rates for modems Half-Duplex Full-Duplex Encoding 2400 4800 7200 9600 12,000 14,400 16,800 1200 2400 3600 4800 6000 7200 8400 ASK, FSK, 2-PSK 4-PSK, 4-QAM 8-PSK, 8-QAM 16-QAM 32-QAM 64-QAM 128-QAM 256-QAM 19,200 9600

  45. MODEMs(cont’d) • Modem Standards • Bell modem • The first commercial modems in the early 1970s • ITU-T modem

  46. MODEMs(cont’d) • Bell Modems(cont’d) For flow control or error control

  47. MODEMs(cont’d) • Bell Modems • 212 --> 201 : Same technology, data rate double

  48. MODEMs(cont’d) • ITU-T Modem Standards(cont’d)

  49. MODEMs(cont’d) • ITU-T Modem Standards

  50. MODEMs(cont’d) • ITU-T/Bell Compatibility ITU-T Bell Baud Rate Bit Rate Modulation V.21 V.22 V.23 V.26 V.27 V.29 103 212 202 201 208 209 300 600 1200 1200 1600 2400 300 1200 1200 2400 4800 9600 FSK 4-PSK FSK 4-PSK 8-PSK 16-QAM

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