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

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)

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

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

Digital Data Transmission(cont’d) Parallel transmission

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

Digital Data Transmission(cont’d) Serial Transmission

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

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)

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

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

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

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

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)

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)

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

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

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

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

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

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

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

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

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

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

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

Other Interface Standards (cont’d) DB-37 pins 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 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 Receive Common Terminal in service Select ready Signal quality New signal Standby indicator Send common I II

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

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)

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

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

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

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

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)

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

6.4 MODEMs The most familiar type of DCE

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

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

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

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.

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

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

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

MODEMs(cont’d) Encoding Half-Duplex Full-Duplex ASK, FSK, 2-PSK PSK and QAM(비교) Theoretical bit rates for modems 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

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

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

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

MODEMs(cont’d) ITU-T Modem Standards(cont’d)

MODEMs(cont’d) ITU-T Modem Standards

MODEMs(cont’d) ITU-T Bell Baud Rate Bit Rate Modulation V.21 V.22 V.23 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

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

MODEMs(cont’d) Command Meaning Parameters A B D E H L P T AT commands Command Meaning Parameters A B D E H L P T The number to dial 0 or 1 n 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

MODEMs(cont’d) Traditional Modems

MODEMs(cont’d) 56K Modem

MODEMs(cont’d) Cable Modem