1 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) 6.5 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) zparallel Transmission ~ By grouping, we can send data n bits at a time instead of one  장점 : 속도 (speed)  단점 : 고가 (expansive) 전송거리 (short distance): 최대 25 feets

4 Digital Data Transmission(cont’d) zParallel transmission

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

6 Digital Data Transmission(cont’d) zSerial 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 z 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 단 말장치  DCE(Data Circuit-terminating Equipment) : 데이터 처리 종단 장치

10 DTE-DCE Interface(cont’d) zDTE(Data Terminal Equipment) ~ is any device that is a source of destination for binary digital data yterminal ymicrocomputer ycomputer yprinter yfax machine and so on

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

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

13 DTE-DCE Interface(cont’d) zStandards yEIA x EIA-232 x EIA-442 x EIA-449 yITU-T  V series ( 전화망에 관한 데이터 통신 )  X series ( 데이터 통신망에 대한 데이터통신 )

14 DTE-DCE Interface(cont’d) zEIA-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) zsending 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) zcontrol 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) z 예 : synchronous full-duplex transmission

19 DTE-DCE Interface(cont’d)

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

21 DTE-DCE Interface(cont’d) zCrossing Connections zNull modem pin connection

Other Interface Standards ~ needs more speed and/or distance yEIA-449 yEIA-530 yX.21

23 Other Interface Standards(cont’d) zEIA-449 yDB-37 pin yDB-9 pin zDB-37 and DB-9 connections

24 Other Interface Standards(cont’d) zPin Functions ycategory I pins ~ are compatible with those of EIA-232 ycategory II pins ~ have no equivalent in EIA-232

25 Other Interface Standards(cont’d) zDB-37 pins PinFunctionsCategoryPinFunctionsCategory 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 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 I II I II I II I II I II I II

26 Other Interface Standards(cont’d) zDB-9 pins PinFunction EIA-232 Equivalent Shield Secondary receive ready Secondary send data Secondary receive data Signal ground Receive common Secondary request to send Secondary clear to send Send common

27 Other Interface Standards(cont’d) zElectrical specification : RS-423 and RS-422 ~ EIA-449 uses two other standards to define its electrical specification yRS-423 (unbalanced circuits) yRS-422 (balanced circuits)

28 Other Interface Standards(cont’d) zRS-423 : Unbalanced Mode

29 Other Interface Standards(cont’d) zRS-422 : Balanced Mode

30 Other Interface Standards(cont’d) zCanceling of noise using balanced mode

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

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

33 Other Interface Standards zDB-15 pins PinFunction Pin Function Shield Transmit data or control Control Receive data or control Indication Signal element timing Bye timing Signal ground Transmit data or control Control Receive data or control Indication Signal element timing Byte timing Reserved

MODEMs ~ the most familiar type of DCE

35 MODEMs(cont’d) zMODEM ~ stands for modulator/demodulator yModulator : converts a digital signal to an analog signal yDemodulator : converts an analog signal to a digital signal

36 MODEMs(cont’d) zTransmission yBandwidth ~ 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) zTelephone line bandwidth ~ A telephone line has bandwidth of almost 3000 Hz

38 MODEMs(cont’d) zModem speed yASK(Amplitude Shift Keying) zBaud rate in half-duplex ASK

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

40 MODEMs(cont’d) zFSK(Frequency Shift Keying) zBaud rate in half-duplex FSK

41 MODEMs(cont’d) zPSK and QAM( 비교 ) Encoding Half-DuplexFull-Duplex ASK, FSK, 2-PSK 4-PSK, 4-QAM 8-PSK, 8-QAM 16-QAM 32-QAM 64-QAM 128-QAM 256-QAM ,000 14,400 16, ,

42 MODEMs(cont’d) zModem Standards yBell modem yITU-T modem

43 MODEMs(cont’d) zBell Modems(cont’d)

44 MODEMs(cont’d) zBell Modems

45 MODEMs(cont’d) zITU-T Modem Standards(cont’d)

46 MODEMs(cont’d) zITU-T Modem Standards

47 MODEMs(cont’d) zITU-T/Bell Compatibility ITU-TBellBaud RateBit RateModulation V.21 V.22 V.23 V.26 V.27 V FSK 4-PSK FSK 4-PSK 8-PSK 16-QAM

48 MODEMs(cont’d) zIntelligent Modems ~ contain software to support a number of additional function, such as automatic answering and dialing yAT Command[parameter] command[parameter]… yEx) ATDT

49 MODEMs(cont’d) zAT commands CommandMeaningParameters ABDEHLPTABDEHLPT 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 The number to dial 0 or 1 n