1 kyung hee university prof. choong seon hong transmission of digital data : interfaces and modems

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Kyung Hee University

Prof. Choong Seon HONG

Transmission of Digital DATA :Transmission of Digital DATA :Interfaces and ModemsInterfaces and Modems

22


66 장장 Transmission of Digital Data:Transmission of Digital Data:Interfaces and MODEMsInterfaces and MODEMs

6.1 Digital Data Transmission

6.2 DTE-DCE Interface

6.3 Other Interface Standards

6.4 모뎀 (MODEM)

33


6.1 Digital Data Transmission6.1 Digital Data Transmission

Primary concern when considering the transmission of data

from one device to another is the wiring

44


Digital Data Transmission(cont’d)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

55



Parallel transmission

66



Serial Transmission

one bit follows another

장점 : 단일 channel, 저가

단점 : require interface converter

77



Serial Transmission

88


Digital Data Transmission(cont’d)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

99


Digital Data TransmissionDigital 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)

1010


6.2 DTE-DCE Interface6.2 DTE-DCE Interface

DTE(Data Terminal equipment) : 데이터 단말장치

DCE(Data Circuit-terminating Equipment) : 데이터 회선 종단 장치

1111


DTE-DCE Interface(cont’d)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

1212



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

1313



표준안 (Standards)

defining the connection between a DTE and DCE

1414



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 )

1515



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)

1616



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

1717


DTE-DCE Interface(cont’d)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

1818



기능 규격 (Functional Specification)

1919



Functions of Pins in EIA-232, DB-9

2020



예 : synchronous full-duplex transmission

Step1 :preparation

Step2 : Readiness

Step3 : Set up

Step1 :preparation

Step2 : Readiness

Step3 : Set up

2121



Step4:Data Transfer

Step 5 : Clearing

Step4:Data Transfer

Step 5 : Clearing

2222


DTE-DCE Interface(cont’d)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

2323


DTE-DCE Interface(cont’d)DTE-DCE Interface(cont’d)Crossing Connections

Null modem pin connection

2424


6.3 Other Interface Standards6.3 Other Interface Standards

needs more speed and/or distance

EIA-449

EIA-530

X.21

2525


Other Interface Standards(cont’d)Other Interface Standards(cont’d)

EIA-449

DB-37 pin

DB-9 pin

DB-37 and DB-9 connections

2626



Pin Functions

category I pins

~ are compatible with those of EIA-232

category II pins

~ have no equivalent in EIA-232

2727


Other Interface Standards (cont’d)Other Interface Standards (cont’d)

DB-37 pins

Pin Functions Category Pin Functions Category123456789

10111213141516171819

ShieldSignal rate indicatorUnassignedSend dataSend timingReceive dataRequest to sendReceive timingClear to sendLocal loopbackData modeTerminal readyReceive readyRemote loopbackIncoming callSelect frequencyTerminal timingTest modeSignal ground

202122232425262728293031323334353637

Receive CommonUnassignedSend dataSend timingReceive dataRequest to sendReceive timingClear to sendTerminal in serviceData modeTerminal readyReceive readySelect readySignal qualityNew signalTerminal timingStandby indicatorSend common

IIIIIIIIIIIII

IIIII

IIIIIIIIIIIIIIII

IIIIIII

2828



DB-9 pins

Pin Function EIA-232 Equivalent

123456789

ShieldSecondary receive readySecondary send dataSecondary receive dataSignal groundReceive commonSecondary request to sendSecondary clear to sendSend common

1

14167

121913

2929



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)

3030



RS-423 : Unbalanced Mode

3131



RS-422 : Balanced Mode

3232



Canceling of noise in balanced mode

3333



EIA-530

is a new version of EIA-449 that uses DB-25 pins

3434


Other Interface Standards(cont’d)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)

3535


Other Interface StandardsOther Interface Standards

DB-15 pins

Pin Function

12345678

Pin

9101112131415

Function

ShieldTransmit data or controlControlReceive data or controlIndicationSignal element timingBye timingSignal ground

Transmit data or controlControlReceive data or controlIndicationSignal element timingByte timingReserved

3636


6.4 MODEMs6.4 MODEMs

The most familiar type of DCE

3737


MODEMs(cont’d)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

3838



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

3939


MODEMs(cont’d)MODEMs(cont’d) Telephone line bandwidth

A telephone line has bandwidth of almost 3000 Hz

4040



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.

4141



Baud rate in full-duplex ASK

Although ASK has a good bit rate, it is not used today because of noise

4242



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

4343



Baud Rate in Full-Duplex FSK

4444



PSK and QAM( 비교 )

Encoding Half-Duplex Full-Duplex

ASK, FSK, 2-PSK4-PSK, 4-QAM8-PSK, 8-QAM16-QAM32-QAM64-QAM128-QAM

256-QAM

2400480072009600

12,00014,40016,800

1200240036004800600072008400

19,200 9600

Theoretical bit rates for modemsTheoretical bit rates for modems

4545



Modem Standards

Bell modem

The first commercial modems in the early 1970s

ITU-T modem

4646



Bell Modems(cont’d)

For flow control or error control

4747



Bell Modems

212 --> 201 : Same technology, data rate double

4848



ITU-T Modem Standards(cont’d)

4949



ITU-T Modem Standards

5050



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

5151



Intelligent Modems

~ contain software to support a number of additional function, such as automatic answering and dialing

AT Command[parameter] command[parameter]…

Ex) ATDT4088648902

5252



AT commands

Command Meaning Parameters

ABDEHLPT

Put modem in answer modeUse V.22bis at 1200 bpsDial the numberEnable/disable echo printingPut modem on/off hookAdjust speaker volumeUse pulse dialingUse tone dialing

The number to dial0 or 10 or 1n

5353


MODEMs(cont’d)MODEMs(cont’d) Traditional Modems

5454



56K Modem

5555



Cable Modem

1 kyung hee university prof. choong seon hong transmission of digital data : interfaces and modems

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