1. 6장 Transmission of Digital Data: Interfaces and MODEMs
6.1 Digital Data Transmission
6.2 DTE-DCE Interface
6.3 Other Interface Standards
6.4 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)
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): 최대 25 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
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 II 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37
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

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 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
Transmit data or control
Control
Receive data or control
Indication
Signal element timing
Byte timing
Reserved

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 Baud rate in half-duplex ASK
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) Encoding Half-Duplex Full-Duplex
ASK, FSK, 2-PSK
4-PSK, 4-QAM
8-PSK, 8-QAM
16-QAM
32-QAM
64-QAM
128-QAM
2400
4800
7200
9600
12,000
14,400
16,800
1200
2400
3600
4800
6000
7200
8400
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
1600
2400
300
1200
2400
4800
9600
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) ATDT

49. MODEMs(cont’d) AT commands Command Meaning Parameters 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
The number to dial
0 or 1 n

50. 6.5 요약