Topic 2 Basic Concept Of Data Communication

Understand types of interfaces

Understand MODEM (Modulation-Demodulation).

DEPARTMENT OF

ELECTRICAL ENGINEERING

EP601 DATA

COMMUNICATION

1

At the end of this learning session, student must be able to;

Explain the importance of interface.

List type of electrical interfaces and its application.

RS232C/V.24, RS422/V.11, RJ45, USB

Build straight through and cross over cable using RJ45.

Explain characteristic interface RS232C/V.24 and RS422/V.11:

Electrical , Mechanical , Functional

Explain the importance of MODEM.

List type of modulations:

Analogue , Digital

Point out the characteristic of MODEM:

Asynchronous , Synchronous

Illustrate the operation of synchronous MODEM.

2

Interfaces

A set of wire that connect DTE and DCE.

Interface is required in order to DTE and

DCE communicate each other

Interface enable the data and control

information to be exchanged between DTE

and DCE

3

Types of electrical interface

RS232C/V.24

RS422/V.11,

RJ45

USB

Differences in the standards

include :

Mode of transmission

(single vs. differential)

Data transmission rates

Type of transmission line

and its length.

Characteristic of interface

Mechanical actual physical connection of the DTE to the DCE, terminator connector,

male or female.

Electrical voltage level and timing of voltage level, data rates, distances

Functional specify the function of each terminal (data, control, timing and electrical

ground)

Procedural specify the sequence of events for transmitting data based on the

functional characteristics

RS232-C/V.24

RS232 is a serial interface by Electronic Industries

Alliance (EIA) or known as EIAs Recommended Standard (RS)

RS232-C is the latest version of RS232 (1969).

Used to connect DTE and DCE (i.e modems and

Personal Computers)

RS232-C is identical to CCITT V.24/V.28. CCITT has

split the interface into its electrical description (V.28)

and a mechanical part (V.24).

Specifies mechanical, electrical ,functional and

procedural aspects of the interface

RS232-C/V.24 : Mechanical

Specifications

7

Use standard 25-pin D-shell connector (DB25)

A male D-shell connector is used on DTE and a

female on DCE

This connector is the terminating plug or socket

on a cable running from a DTE or DCE.

Some use a 9-pin D-shell connector (DB9)

instead of the 25-pin connector.

This connector provides the means to transmit

and receive the necessary signals for modem

applications

RS-232 DB-25 & DB-9 Connectors

8

DB-25 Female

DB-25 Male

DB-9 Female

DB-9 Male

RS232 Standards : Connectors

RS232-C/V.24 : Electrical Specifications

Mode of

operation :

single-ended (unbalanced)

Cable length : 50 feet max.

Data rate : 20 kbps max.

Signal State:

Mark :

(logical 1)

Signal State:

Space :

(logical 0)

Transmitter Voltage Range: -15V to -5V

Receiver Voltage Range:-25V to -3V

Transmitter Voltage Range: +5V to

+15V

Receiver Voltage Range:+3V to +25V

signals are represented by

a voltage with reference

to a common signal

ground.

RS232-C/V.24 :Functional

Specifications

11

Specifies the role of the individual circuits

Data circuits in both directions allow full-duplex

communication

The circuit can be group into the categories of

data, control, timing and ground.

Timing signals allow for synchronous

transmission

Pin Name Function

2 Transmitted

Data (TD) This signal is generated by the DTE and received

by the DCE.

3 Received

Data (RD) This signals is generated by the DCE and

received by the DTE.

4 Request to

Send (RTS) When the host system (DTE) is ready to transmit

data to the peripheral system (DCE), RTS is turned

ON. After RTS is asserted, the DCE must assert CTS before communication can commence.

RS232-C/V.24 :Functional Specifications cont

5

5

6

Clear to

Send (CTS)

Data Set

Ready

(DSR)

CTS is used along with RTS to provide handshaking between the DTE and the DCE.

After the DCE sees an asserted RTS, it turns CTS

ON when it is ready to begin communication.

This signal is turned on by the DCE to indicate

that it is connected to the telecommunications

line

8 Data

Carrier

Detect

(DCD)

This signal is turned ON when the DCE is

receiving a signal from a remote DCE which

meets its suitable signal criteria. This signal

remains ON as long as the a suitable carrier signal can be detected.

RS232-C/V.24 :Functional Specifications

cont

20 Data

Terminal

Ready

(DTR)

DTR indicates the readiness of the DTE. This

signal is turned ON by the DTE when it is ready

to transmit or receive data from the DCE. DTR

must be ON before the DCE can assert DSR.

22 Ring

Indicator

(RI):

RI, when asserted, indicates that a ringing

signal is being received on the communications

channel.

RS232-C/V.24 :Functional Specifications

cont

Connection Establishment

Dial Up Operation (1)

Dial Up Operation (2)

Dial Up Operation (3)

RS-422/V.11

RS-422 also called EIA-422 is a technical standard that specifies electrical characteristics of a digital signaling circuit

The RS-422 standard defines a balanced (or differential) data communications interface using two separate wires for each signal (Transmit + and Transmit -, Receive + and Receive -)

Data transmission at higher speeds and longer distances than EIA-232.

Used in point-to-point communications.

Maximum distance and rate : a) 1200 meter/ 4000 feet @ max. 100 kbps b) 10 Mbps @ 12 meter/ 50 ft V.11 is the international equivalent ITU-T for RS-422.

RS-422/V.11 cont.

Electrical - Voltage Level:

a) Transmitting

low logic 0 : + 2 V to + 6 V

high logic 1 : - 2 V to - 6 V

b) Receiving

low logic 0 : + 0.2 V to + 6 V

high logic 1 : - 0.2 V to - 6 V

c) Noise margin : ( 2 0.2 ) V = 1.8 V

RS422 Voltage Transition Level

RS-422/V.11 cont.

Comparison Item

RS232/ V.24 RS422/V.11

Signal Lines On lines which share a

common zero

Each signal line consists

of two wires, preferably twisted to reduce noise

Connection

to Receiver

Only designed to serve

one receiver

Line driver can serve up

to ten receivers in parallel.

Cable Length

Interface between

computers, printers and

terminals with modems

Direct connection of

intelligent devices, without the need of

modems

Comparison between RS232 and RS422

RS-422/V.11 cont.

RJ45

RJ45 is a type of connector commonly used for

network cable.

The "RJ" in RJ45 stands for "registered jack" since it is

a standardized networking interface. The "45"

simply refers to the number of the interface

standard.

Each RJ45 connector has eight pins, which means

an RJ45 cable contains eight separate wires.

Straight-through and cross-over wiring using RJ-45 cables

RJ-45 conductor data cable contains 4 pairs of wires ,

each consists of a solid colored wire and a stripe of the

same color.

There are two wiring standards for RJ-45 wiring: T-568A

and T-568B.

10BaseT/100BaseT Ethernet uses only 2 pairs: Orange

and Green.

The other two colors (blue and brown) may be used for

a second Ethernet line or for phone connections.

The unused pins are generally connected straight-

through in both straight-through and cross-over cables.

T-568A and T-568B Standard.

10BaseT/100BaseT Ethernet

The 10Base-T standard (also called Twisted Pair

Ethernet) uses a twisted pair cable with

maximum lengths of 100 meters.

The 10Base-T system operates at 10Mbps and

uses baseband transmission methods.

100BaseT Ethernet is a Fast Ethernet standard

that carry traffic at the nominal rate of

100 Mbit/s.

Straight-through wiring using RJ45 cable

Used to connect DTE to DCE, such as computers to

modems or hubs.

Use either T-568A or T-568B on both ends of the

cable.

Uses only 2-pairs of wires:

Orange (pins 1 & 2)

Green (pins 3 & 6)

Connects pin 1 to pin 1, pin 2 to pin 2, pin 3 to pin 3,

and pin 6 to pin 6.

The unused pins are generally connected straight-

through in both straight-through and cross-over

cables.

Straight

through

T-568A

T-568B

Cross-over wiring using RJ45 cable

Used to connect DTE to DTE, or DCE to DCE

equipment; such as computer to computer,

computer to router; or gateway to hub.

To create a cross-over cable, you'll wire T-568A on

one end and T-568B on the other end of the cable.

Connects pin 1 to pin 3, pin 2 to pin 6, pin 3 to pin 1

and pin 6 to pin 2.

The unused pins are generally connected straight-

through in both straight-through and cross-over

cables.

Cross-over

T-568B T-568A

USB USB or Universal Serial Bus is a popular option for

external device communication.

USB was designed to standardize the connection of

computer peripherals (i.e keyboards, digital

cameras, printer)

USB 2.0 (High speed) is very fast, 480 Mb/s, USB 1

(Full Speed) is 12 Mb/s.

Its a 4-wire system, point-to-point system.

One advantage of USB is that it can provide power

for external hardware.

Standard type A plug and receptacle

USB to Other Devices

Connection

Cables

33

USB to Serial

Adapter

USB to Internet

USB to Camera USB to Serial Adapter

USB to

Scanner

Types

of USB

Cable

34

USB Specification

USB 1.0: Specifies data rates of 1.5 Mbit/s (Low-

Bandwidth, is mostly used for Human Input Devices

(HID) such as keyboards, mouses, joysticks and

often the buttons on higher speed devices such as

printers or scanners) and 12 Mbit/s (Full-Bandwidth)

USB 2.0: In addition to USB 1.0 adds signaling rate of

480 Mbit/s (Hi-Speed).compatible with USB 1.0, but

some hardware designed for USB 2.0 may not work

with USB 1.0 host controllers.

USB 3.0: Added transmission rates up to 5 Gbit/s

(SuperSpeed)

35

USB Version

36

MODEM

Modems

Modems are devices which allow digital data signals to be transmitted across an analogue link.

Modem stands for MOdulator/DEModulator.

A modem changes the digital signal to an analogue frequency : converts the signal to analog by varying the amplitude, frequency, or phase and sends this tone across the analogue link. At the other end, another modem receives the signal and converts it back to digital.

A modem may be an internal modem or it may be external.

The importance of MODEM or , why is a

modem needed we need a converter so data can be transferred

to the analogue system of the telephone.

for giving higher quality and faster transfer of data. gives fast communication which is needed by many people.

giving good quality of graphics for bigger applications.

for creating the local area network for homes or offices.

for facilitating the fast growth of the economy of a country.

to reach/communicate remote places by computer

MODEM

Structure of Modem

UART

Mod/ Demod Circuit

Transmitter Filter/ Receiver Filter

Buffer

Carrier Tracer

40

COMPUTER

MOD / DEMOD

CIRCUIT

CARRIER

TRACER

UART

RECEIVER

FILTER

TRANSMITTER

FILTER

B

U

F

F

E

R

TO PSTN

Basic modem diagram

41

MODEM cont

Block Diagram for Each Part

Transmitter: Computer, UART, MOD circuit,

transmitter filter, buffer, PSTN.

Receiver: PSTN, buffer, receiver filter and carrier

tracer, DEMOD circuit, UART, computer.

42

UART

Transmitting: Parallel data from computer

change to serial data.

Receiving: Serial data from receiver change to

parallel data.

MOD/ DEMOD Circuit

Mod: change data from digital data to

telephone signal (analog signal).

Demod: change data from telephone signal

(analog signal) to digital data.

43

Function for Each Block

MODEM cont

Transmitter/ Receiver Filter

Filtering the signal before transmit / receive.

Buffer

Create a standard transmission signal level and impedance appropriate to telephone

Carrier Tracer

Trace the data input and inform to the computer.

44

Function for Each Block cont..

MODEM cont

Types of Modem External Internal

PC Card Wireless

45

MODEM cont

Types of Modem External

Digital Modem

1. Channel Service Unit (CSU)/ Digis Service Unit (DSU) modem:

Communication with digital modem technique as a Digital Transmission Service (DTS).

2. Digital Modems Converts the RS-232 digital signals to digital signals more suitable for transmission.

46

MODEM cont

Types of Modem External cont

3. Optical Modems:

Uses optical fiber cable instead of wire. The modem converts the digital signal to pulses of light to be transmitted over optical lines.

47

MODEM cont

48

Types of Modem External cont

4. Short Haul Modem:

Modems used to transmit over 20 miles or less.

Modems we use at home or to connect

computers together between different offices in

the same building.

49

MODEM cont

Types of Analog Modem

1. Acoustic Coupler Modem:

A modem that coupled to the telephone

handset with what looked like suction cups that

contained a speaker and microphone. Used for

connecting to hotel phones for travelling sales

people.

50

MODEM cont

Types of Analog Modem cont

2. Smart Modem

Modem with a CPU (microprocessor) on board

that uses the Hayes AT command set. This allows

auto-answer & dial capability rather than

manually dialing & answering.

51

MODEM cont

Modulation

modulation is the process of varying one or more

properties of a high-frequency waveform called the

carrier signal, with a modulating signal which

contains information to be transmitted

Types of modulation :

Analogue modulation

Pulse Modulation

Digital modulation

Analog Modulation

Amplitude

Modulation (AM)

Frequency

Modulation (FM)

Phase

Modulation (PM)

Amplitude Modulation (AM)

Amplitude modulation is the process of varying the

amplitude of the sinusoidal carrier wave by the

amplitude of the modulating signal.

Frequency Modulation (FM) FM conveys information over a carrier wave

by varying its instantaneous frequency. This

contrasts with AM, in which the amplitude of

the carrier is varied while its frequency remains constant.

Phase modulation (PM)

Phase Modulation changes the phase of the

carrier. The phase of the carrier is switch each time

that a one (1) bit is required, but does not change

for the duration of the zero (0) bit.

Phase modulation (PM) is a modulation that

represents information as variations in the

instantaneous phase of a carrier wave. OR A type

of electronic modulation in which the phase of a

carrier wave is varied in order to transmit the

information contained in the signal.

The signal might has changed phase by +180 or -

180.

Phase modulation (PM) cont

Digital Modulation

The parameters of the carrier that can be

modified are the amplitude, the frequency,

and the phase.

Amplitude Shift Keying (ASK)

Frequency Shift Keying (FSK)

Phase Shift Keying (PSK)

Amplitude-shift keying (ASK)

Amplitude-shift keying (ASK) is a form of modulation

that represents digital data as variations in the

amplitude of a carrier wave.

In its simplest form, a burst of radio frequency is

transmitted only when a binary 1 appears and is

stopped when a 0 appears. In another variation,

the 0 and 1 are represented in the modulated

signal by a shift between two preselected

amplitudes.

Frequency Shift Keying (FSK)

In the simplest form of FSK signaling, digital data is

transmitted using one of two frequencies, where by

one frequency is used to transmit a 1 and the other

frequency to transmit a 0.

Phase Shift Keying (PSK)

In PSK, we change the phase of a sinusoidal carrier to indicate information. To transmit 0, we

shift the phase of the sinusoid by 180. Phase

shift represents the change in the state of the

information.

Quadrature Amplitude Modulation (QAM)

(Quadrature Amplitude Modulation) A modulation

technique that employs both phase modulation

(PM) and amplitude modulation (AM).

In digital QAM, the input stream is divided into

groups of bits based on the number of modulation

states used. For example, in 8QAM, each three bits

of input, which provides eight values (0-7) alters

the phase and amplitude of the carrier to derive

eight unique modulation states (see example

below

Quadrature Amplitude Modulation (QAM)

Sample of QAM waveform

Concept of Asynchronous Modem

Random transmission No synchronization clock

The number of character bits are acknowledged

Every data transmission needs start bit, stop bit and parity bit

Asynchronous modems usually operate in FSK modulation

Operate in slow and moderate rates , up to 1800 bps

Less efficient due to the high number of control bits

Advantages : easy control of data errors

Use of synchronization clock

More efficient due to the low number of control bits

The usual modulation methods are PSK modulation or QAM

In synchronous modems, equalizers are used, in order to offset the misfit of the telephone lines.

Operates at higher rates , between 2400 bps and 56000 bps over standard voice-grade telephone

Concept of Asynchronous Modem

cont

Synchronous Modem

- block diagram -

Synchronous Modem Transmission/ Receiving

Block Diagram

Timing

Scramble/

Descramble

Phase Modulation

/ Demodulation

Equalizer

DAC/

ADC

Clock

Data

PSTN

Function of each block for Transmitter/ Receiver

1. Clock (timing source): generate all the timing references require for all transmit or receive operation.

2. Scrambler/ Descrambler : change the data from random signal to the original signal / change the data from original signal to the random signal.

3. Phase Modulation/ Phase Demodulation : the data will be phase modulating / phase demodulating.

67

Function of each block for Transmitter/ Receiver cont..

4. ADC/ DAC Analog to Digital Converter: change analog signal to digital signal/ Digital Analog Converter: change digital signal to analog signal

5. Equalizer: Increase and stabilize the signal to high frequency.

68

Application of Synchronous Modem

and Asynchronous Modem

Connecting a host computer to remote

terminals that are polled using asynchronous

polling protocols

Connecting SCADA host computers to RTU's

Connecting host computers to terminals

using synchronous financial industry

protocols (HDLC, SDLC, etc)

69

Application of Synchronous Modem

and Asynchronous Modem cont

Collecting data from multiple data

sources into a single remote port

70

REFERENCES:

Main:

Forouzan, B.A. (2012). Data Communications

and Networking (5th edision). Mc Graw Hill.

(ISBN: 978-0-07-131586-9)

Additional:

William Stallings. (2011). Data And Computer

Communication (9th edition). Prentice Hall.

(ISBN-10: 0131392050)