Data CommunicationData Communication

It is the process of communicating It is the process of communicating information in binary form between two information in binary form between two pointspoints

Sometimes called “Computer Sometimes called “Computer Communication”, because most of the Communication”, because most of the information interchanged today is between information interchanged today is between computers.computers.

Early forms of Communications Early forms of Communications

Puffs of smokePuffs of smoke

Reflections of sunlight from a hand-held Reflections of sunlight from a hand-held mirrormirror

Signal flagsSignal flags

LanternsLanterns

Early uses of ElectricityEarly uses of Electricity

17531753 – early proposal to a scottish – early proposal to a scottish magazine, based from the 26 parallel magazine, based from the 26 parallel wires from town to town, one wire for each wires from town to town, one wire for each letterletter

18331833 – Carl Friedrich Gauss used a code – Carl Friedrich Gauss used a code based on a 5 by 5 matrix of 25 letters (I & based on a 5 by 5 matrix of 25 letters (I & J combined) to send messages by J combined) to send messages by deflecting a needle from one to five times, deflecting a needle from one to five times, right-leftright-left

TelegraphTelegraph

First notable development in data First notable development in data communications in 19communications in 19thth century based on century based on electric power.electric power.

Invented by Samuel F. B. Moorse (Finley Invented by Samuel F. B. Moorse (Finley Breese)Breese)

Samuel F.B. MoorseSamuel F.B. Moorse

Morse Code Morse Code

1844 – best-know demonstration of 1844 – best-know demonstration of telegraph using the morse code.telegraph using the morse code.

Morse transmitted over a wire from Morse transmitted over a wire from Washington to Baltimore the message Washington to Baltimore the message “What hath God wrought!”“What hath God wrought!”

1866 – the telegraph connected the 1866 – the telegraph connected the nations of the world with the laying of nations of the world with the laying of the trans-Atlantic cable between the the trans-Atlantic cable between the United States and FranceUnited States and France

Two-state Communication Two-state Communication SystemSystem

It is the simplest, the easiest to build, and It is the simplest, the easiest to build, and the most reliable. The states can be On the most reliable. The states can be On and Off (telegraph), Plus & Minus(current and Off (telegraph), Plus & Minus(current flowing), Light & Dark(flashlight), 1 & 0 flowing), Light & Dark(flashlight), 1 & 0 (computer)(computer)

Mark and Space Mark and Space

Worldwide standards for data Worldwide standards for data communicationscommunications

Marking Condition –Marking Condition – idle condition on the idle condition on the transmission channel.transmission channel.

Bits and BytesBits and Bytes

Binary digit – commonly referred to as a Binary digit – commonly referred to as a bit, represented by 0 & 1.bit, represented by 0 & 1.

Byte – several bits combined in uniform Byte – several bits combined in uniform group.group.

Communication CodesCommunication Codes

CodesCodes

Agreed-upon-in-advance meanings Agreed-upon-in-advance meanings between signaling elements and between signaling elements and

characters.characters.

CharactersCharacters

The letters, numerals, space, punctuation The letters, numerals, space, punctuation marks, and other signs and symbols on a marks, and other signs and symbols on a

keyboardkeyboard

Signaling ElementsSignaling Elements

Something that is sent over a transmission Something that is sent over a transmission channel and used to represent a character channel and used to represent a character

Ex. Dot and dashes or O’s and 1’sEx. Dot and dashes or O’s and 1’s

CodesCodes

Baudot Code

Modern Codes– EBCDIC– ASCIIASCII

Baudot Code

Developed in 1870 by a Frenchman Developed in 1870 by a Frenchman named Emile Baudot.named Emile Baudot.It used same number of signaling It used same number of signaling elements to represent each characterelements to represent each characterIt was better suited to machine encoding It was better suited to machine encoding and decoding.and decoding.Based from 5-bit code could generate only Based from 5-bit code could generate only 32 possible combinations.32 possible combinations.

Modern Codes

CCITT International Alphabet No. 2 CCITT International Alphabet No. 2 ((International Telegraph and Telephone International Telegraph and Telephone Consultative Committee Consultative Committee ) ) – a single 5-bit – a single 5-bit code still used for telex transmissioncode still used for telex transmission

EBCDICEBCDIC

ASCIIASCII

EBCDIC ((Extended Binary Coded Extended Binary Coded

Decimal Interchange CodeDecimal Interchange Code))

Developed by IBM and primarily used Developed by IBM and primarily used for synchronous communication for synchronous communication systems attached to a large mainframe systems attached to a large mainframe computerscomputers

8-bit code, allowing 256 characters to 8-bit code, allowing 256 characters to be represented.be represented.

ASCIIASCII((American Standard Code For American Standard Code For

Information InterchangeInformation Interchange))

It was defined by American National It was defined by American National Standards Institute (ANSI) in the US by Standards Institute (ANSI) in the US by the International Standards Organization the International Standards Organization (ISO)(ISO)

7-bit code, formally known as ANSI 7-bit code, formally known as ANSI Standard X3.4-1977 that can represent Standard X3.4-1977 that can represent 128 characters.128 characters.

Extended ASCII - IBM PC in 1981Extended ASCII - IBM PC in 1981

Escape CharacterEscape Character(ESC)(ESC)

Designates that the codes that follow have Designates that the codes that follow have special meaning.special meaning.

It has the effect of making all character It has the effect of making all character codes available for control of a device.codes available for control of a device.

Escape SequenceEscape Sequence – code sequences – code sequences made up of noncontrol characters that are made up of noncontrol characters that are to be interpreted as control codes. to be interpreted as control codes.

TeleprintersTeleprinters

Next major step after the telegraph in data Next major step after the telegraph in data communications.communications.

Backbone of nonvoice business Backbone of nonvoice business communications for over half a centurycommunications for over half a century

Teletypwriter (TTY) – a teleprinter with a Teletypwriter (TTY) – a teleprinter with a keyboard for input, standard terminal for keyboard for input, standard terminal for small-and medium-size computerssmall-and medium-size computers

Two Nationwide Public Two Nationwide Public TeleprinterTeleprinter

TWX - Teletypewriter Exchange Service TWX - Teletypewriter Exchange Service

TELEX - ITELEX - International telegraphic nternational telegraphic message-transfer service consisting of a message-transfer service consisting of a network of teleprinters. network of teleprinters.

Data Communications in Data Communications in ComputingComputing

The 1950sThe 1950s

Typical computer system used punched Typical computer system used punched cards for input, printers for output, reels for cards for input, printers for output, reels for magnetic tape for “permanent” mass magnetic tape for “permanent” mass storage.storage.There was little or no data communications There was little or no data communications in these system because the input devices, in these system because the input devices, output devices and computer were all output devices and computer were all located close together and were directly located close together and were directly connected by short cables.connected by short cables.Information was processed on a “one job at Information was processed on a “one job at a time” or “batch” basis.a time” or “batch” basis.

The 1960sThe 1960s

In the 1960s, the use of outlying, on-lie In the 1960s, the use of outlying, on-lie terminals required communications links to terminals required communications links to coonect them to the main computercoonect them to the main computer

The 1970sThe 1970s

The introduction of the minicomputer and The introduction of the minicomputer and the very portable microcomputer required the very portable microcomputer required that these units have increased that these units have increased communications with their mainframe communications with their mainframe computercomputer

The 1980sThe 1980s

Advances in technology increased the Advances in technology increased the capabilities, reduced the size and power capabilities, reduced the size and power requirements of computers, and provided requirements of computers, and provided a new communications link – the satellitea new communications link – the satellite

The 1990sThe 1990s

Installation of appropriate adapter card in Installation of appropriate adapter card in each personal computer, cabling and each personal computer, cabling and software, local area netwoks (LANs)software, local area netwoks (LANs)

Devices used in NetworkingDevices used in Networking

Gateways Gateways – enabled personal computers – enabled personal computers on selected LANs to access corporate on selected LANs to access corporate mainframe computer.mainframe computer.

Brigdes Brigdes – enable data to be transmitted – enable data to be transmitted between two LANs supporting the same between two LANs supporting the same transmission protocol, allowing electronic transmission protocol, allowing electronic messages, data files, and programs to be messages, data files, and programs to be sent between users on different network.sent between users on different network.

Routers Routers – examines data destination – examines data destination addresses and route data over different addresses and route data over different circuits based upon those addresses circuits based upon those addresses enabled a lesser number of lines to be enabled a lesser number of lines to be used for interconnecting many LANs.used for interconnecting many LANs.

LAN

LAN

Bridge

Bridge

PC

PC PC

PC

PC Gateway

Router

PC

Mainframe Computer

To different warehouse

Changes in the IndustriesChanges in the Industries

In modern communication systems, we In modern communication systems, we can interconnect equipment of many can interconnect equipment of many different sizes and capabilities from a different sizes and capabilities from a variety of suppliers.variety of suppliers.

General Description of a Data General Description of a Data Communications SystemCommunications System

Three Components of Data Three Components of Data Communication SystemCommunication System

The Transmitter (also called the “source”)The Transmitter (also called the “source”)

Transmission Path(usually called the Transmission Path(usually called the channel, but sometimes line)channel, but sometimes line)

The Receiver (occasionally called the The Receiver (occasionally called the “sink”)“sink”)

Universal Seven-Part Data Universal Seven-Part Data CircuitCircuit

The data terminal equipment (DTE) at point The data terminal equipment (DTE) at point A.A.

The interface between the DTE and the data The interface between the DTE and the data circuit-terminating equipment (or the data circuit-terminating equipment (or the data communications equipment) (DCE) at point A.communications equipment) (DCE) at point A.

The DCE at point A.The DCE at point A.

The transmission channel between point A The transmission channel between point A and point Band point B

The DCE at point BThe DCE at point B

The DCE-DTE interface at point BThe DCE-DTE interface at point B

The DTE at point B.The DTE at point B.