6 장 Transmission of Digital Data: Interfaces and MODEMs

1. 6장 Transmission of Digital Data: Interfaces and MODEMs 6.1 Digital Data Transmission 6.2 DTE-DCE Interface 6.3 Other Interface Standards 6.4모뎀(MODEM) 6.5 요약

2. 6.1 Digital Data Transmission ~ of primary concern when considering the transmission of data from one device to another is the wiring

3. 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

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

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

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

7. 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

8. Digital Data Transmission • 동기전송(synchronous transmission) ~ send bits one after another without start/stop bits or gaps. It is the responsibility of the receiver to group the bits • 장점 : 속도(speed)

9. 6.2 DTE-DCE Interface • DTE(Data Terminal equipment) : 데이터 단말장치 • DCE(Data Circuit-terminating Equipment) : 데이터 처리 종단 장치

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

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

12. DTE-DCE Interface(cont’d) • 표준안(Standards) ~ to define the connection between a DTE and DCE

13. DTE-DCE Interface(cont’d) • Standards • EIA • EIA-232 • EIA-442 • EIA-449 • ITU-T • V series (전화망에 관한 데이터 통신) • X series (데이터 통신망에 대한 데이터통신)

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

15. 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

16. DTE-DCE Interface(cont’d) • control and timing ~ Signals must be sent using OFF less than –3 volts and ON greater than +3 volts

17. DTE-DCE Interface(cont’d) • 기능 적인 면(Functional Specification)

18. DTE-DCE Interface(cont’d) • 예: synchronous full-duplex transmission

19. DTE-DCE Interface(cont’d)

20. DTE-DCE Interface(cont’d) • Null Modem ~ not needed to connect two compatible digital devices directly • Using regular data pin connections with and without DCEs

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

22. 6.3 Other Interface Standards ~ needs more speed and/or distance • EIA-449 • EIA-530 • X.21

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

24. 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

25. Other Interface Standards(cont’d) • DB-37 pins 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

26. 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

27. 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)

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

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

30. Other Interface Standards(cont’d) • Canceling of noise using balanced mode

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

32. Other Interface Standards(cont’d) • X.21 ~ is an interface designed by the ITU-T • DB-15 connector

33. 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

34. 6.4 MODEMs ~ the most familiar type of DCE

35. MODEMs(cont’d) • MODEM ~ stands for modulator/demodulator • Modulator : converts a digital signal to an analog signal • Demodulator : converts an analog signal to a digital signal

36. MODEMs(cont’d) • Transmission • 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

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

38. MODEMs(cont’d) • Modem speed • ASK(Amplitude Shift Keying) • Baud rate in half-duplex ASK

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

40. MODEMs(cont’d) • FSK(Frequency Shift Keying) • Baud rate in half-duplex FSK

41. MODEMs(cont’d) • PSK and QAM(비교) 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

42. MODEMs(cont’d) • Modem Standards • Bell modem • ITU-T modem

43. MODEMs(cont’d) • Bell Modems(cont’d)

44. MODEMs(cont’d) • Bell Modems

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

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

47. 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

48. MODEMs(cont’d) • Intelligent Modems ~ contain software to support a number of additional function, such as automatic answering and dialing • AT Command[parameter] command[parameter]… • Ex) ATDT4088648902

49. MODEMs(cont’d) • AT commands Command Meaning Parameters The number to dial 0 or 1 0 or 1 n A B D E H L P T Put modem in answer mode Use V.22bis at 1200 bps Dial the number Enable/disable echo printing Put modem on/off hook Adjust speaker volume Use pulse dialing Use tone dialing