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WHAT IS DATA COMMUNICATIONS ?WHAT IS DATA COMMUNICATIONS ?

Transmission of data and information between two or more computers

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Electronic data interchange (EDI)•Reduced paper flow•Lower transaction costs•Faster transmission of documents•Reduced data entry errors

Global positioning systems (GPSs)•Determine geographic location•Tracking and navigation•Measuring distances

The InternetThe InternetGlobal network of computer networks…

•Electronic mail (e-mail)Electronic mail (e-mail)•Voice mailVoice mail•Facsimile (fax)Facsimile (fax)•TelecommutingTelecommuting•VideoconferencingVideoconferencing•Electronic meetingsElectronic meetings•Desktop videoconferencing…Desktop videoconferencing…

EXAMPLES OF HOW COMMUNICATIONS IS USEDEXAMPLES OF HOW COMMUNICATIONS IS USED

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SENDING UNIT TRANSMISSION RECEIVING UNIT CHANNEL

Computer Telephone Line ComputerTerminal Radio Waves Terminal + Microwaves +software Twisted Pair software

Co-axial Cable Fibre-optic Cable

Satellite

DATA COMMUNICATION COMPONENTSDATA COMMUNICATION COMPONENTS

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MODEM (modulator-demodulator)•Modulation: converting from digital to analog•Demodulation: converting from analog to digital•Enables digital microcomputers to communicate across analog telephone lines.

Data Transmission

•The speed of modems measured in bps(bits per second)

•33.6kbps, 56kbps

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Communication Software

Communications software consists of programs:• help users establish a connection to another computer

or network• manage the transmission of data, instructions, and

information • provide all interface for users to communicate with

one another. Examples of application software for communications:• e-mail, FTP, Web browser, newsgroup / message

boards• chat rooms, instant messaging• video conferencing, and video telephone calls. Features of communication software:• keep database of telephone numbers • automatic redial • act as a terminal • easy sending/receiving of files • data encryption (software at other end must know how

to decrypt it).

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TWO methods.1. Asynchronous transmission2. Synchronous transmission

DATA TRANSFER

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•usually used to describe communications in which data can be transmitted intermittently rather than in a steady stream.•Also called start-stop transmissiondata transmission requiring stop and start bitswhen a byte is sent-> send a start bit 0

followed by 8 data bits-> then a stop bit 1

Most commonly used for the simplest data link, i.e.: terminals to computers.

Asynchronous TRANSMISSION

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SYN = Synchronous chars CS = Check Sum

SYNCHRONOUS TRANSMISSION

•Occurring at regular intervals•no start and stop bits used•no pause between sending characters•involves sending large blocks of characters•each block has special sync characters which are sent at the beginning of these blocks

SYN SYN SYN DATA CS CS

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AsychronousStart 1 char stop 1 bit 8 bits 1 bit1) Send 1000 chars

Data = 1000 x 8 = 8000 bitsExtra = 1000 x 2 = 2000 bitsTotal = 10,000 bits

2) Send 40 charsData = 40 x 8 = 320 bitsExtra = 40 x 2 = 80 bitsTotal = 400 bits

Synchronous VS Asynchronous transmission

SychronousSYN CI Data

CS3 bytes 2 bytes 5 bytes1) Send 1000 chars

Data = 1000 x 8 = 8000 bitsExtra = 10 x 8 = 80 bitsTotal = 8,080 bits

2) Send 40 charsData = 40 x 8 = 320 bitsExtra = 10 x 8 = 80 bitsTotal = 400 bits

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Data transmission

Serial and parallel transmission– Serial data transmission

•Bits flow in a series or continuous stream

•Data sent over telephone lines •Serial port in microcomputers

– RS-232 connector– Asynchronous communication port

– Parallel data transmission•Bits flow through separate lines

simultaneously•Limited to communications over short

distance– System unit to printer

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PROTOCOLSPROTOCOLS

A protocol is a set of rules for the exchange of data between A protocol is a set of rules for the exchange of data between computers..computers..

The TCP/IP (Transmission Control Protocol/Internet The TCP/IP (Transmission Control Protocol/Internet Protocol) permits any computer to communicate with the Protocol) permits any computer to communicate with the InternetInternet

network standard, specifically a protocol, which network standard, specifically a protocol, which defines how messages (data) are routed from one end of a defines how messages (data) are routed from one end of a network to the other, ensuring the data arrives correctly.network to the other, ensuring the data arrives correctly.

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SIMPLEXSIMPLEXIs one way flow of data. Eg. Television

DIRECTION OF DATA COMMUNICATIONSDIRECTION OF DATA COMMUNICATIONS

HALF-DUPLEX AAllows for two-way data transmission, but only one direction llows for two-way data transmission, but only one direction at a time. Eg. CB radio…at a time. Eg. CB radio…

FULL DUPLEXFULL DUPLEX

Is simultaneous, two-way transmissionIs simultaneous, two-way transmission.. Eg. Telephone

Walkie-talkie

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Networks

A network is a group of two or more computer systems linked together via communications devices

transmission media, allowing computers to share resources, such as hardware, software, data, and information.

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NETWORKS & OTHER ISSUESNETWORKS & OTHER ISSUES

What is a Network?• A number of computers or terminals connected together

make up a NETWORK.• Can either be a WAN (Wide area network) or a LAN (Local

area network)• WANs involve using the telephone system,• LANs - privately owned cabling.• Each computer is known as a NODE.

• Computers and devices that allocate resources for a network are called servers.

• The shape of the network is its TOPOLOGY.

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Types of Computer Networks

Local-Area Networks (LANs) : The computers are geographically close together (that is, in the same building).

Wide-Area Networks (WANs) : The computers are farther apart and are connected by telephone lines or radio waves.

Campus-Area Networks (CANs): The computers are within a limited geographic area, such as a campus or military base.

Metropolitan-Area Networks (MANs): A data network designed for a town or city.

Home-Area Networks (HANs): A network contained within a user's home that connects a person's digital devices.

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Consists of:• hardware - PC + additional communications board in the computer• a software package eg Windows XP• cabling joining the computers and other peripheral devices together

LOCAL AREA NETWORK (LAN)LOCAL AREA NETWORK (LAN)

LAN •Allows sharing of software, hardware (server, printers, modems) and information.• Server workstation has large hard disk with application programs & data others can access.• LAN's normally within the same building or complex.• Cabling is usually twisted pair or co-axial

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WIDE AREA NETWORK (WAN)

Wide Area Network (WAN)•Network that covers a large geographic area (such as a city, country or the world) •Typically, a WAN consists of two or more LANs.•Uses communications channel that combines many type of media such as telephone lines, cables and radio waves.•Computers connected to a wide-area network are often connected through public networks, such as the telephone system. They can also be connected through leased lines or satellites.•The Internet is the world’s largest WAN.

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Network Topologies

Network topology is the geometric arrangement of a computer system. Common topologies include a bus, star, and ring

• Ring Topology • Star Topology• Bus Topology

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Ring (Token ring)Ring (Token ring)• Used in LAN's• electronic (data) token sent from workstation to workstation• incoming data read from token.• outgoing data attached to empty token.

StarStar• one or more smaller computers connected to one or more smaller computers connected to a central host (mini or mainframe) eg. banks.a central host (mini or mainframe) eg. banks.• Nodes can communicate only via central Nodes can communicate only via central computer. If host goes down, network is computer. If host goes down, network is inoperable.inoperable.

TYPICAL TOPOLOGIESTYPICAL TOPOLOGIES

•Communication is usually one-way around the ring = no collisions• One node going down disables the network.• Wiring is twisted pair or coaxial cable• Need a Token Ring interface card

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TYPICAL TOPOLOGIES (CONT’D)TYPICAL TOPOLOGIES (CONT’D)

BusBus• All nodes are connected to a single line All nodes are connected to a single line via an interface box.via an interface box.• Even if one of the nodes fails, the Even if one of the nodes fails, the network is not affected.network is not affected.• Nodes can communicate with each other Nodes can communicate with each other without bypassing the server.without bypassing the server.

In buses and rings all nodes receive In buses and rings all nodes receive every signal. Each node determines every signal. Each node determines if the message is addressed to that if the message is addressed to that node either receiving the message or node either receiving the message or passing it on.passing it on.

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Network Communications Technologies

• Ethernet • Token Ring • TCP/IP • 802.11 • Bluetooth • IrDA • WAP• Intranet • Extranet

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Ethernet

Ethernet is a local-area network (LAN) architecture developed by Xerox Corporation in cooperation with DEC and Intel in 1976.

Ethernet uses a bus or star topology and supports data transfer rates of 10 Mbps.

The Ethernet specification served as the basis for the IEEE 802.3 standard, which specifies the physical and lower software layers.

Ethernet uses the CSMA/CD access method to handle simultaneous demands. It is one of the most widely implemented LAN standards.

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Token Ring

Token ring is a network standard in which computers and devices on the network share or pass a special signal, called a token, in a unidirectional manner and in a preset order.

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802.11

802.11 and 802.11x refers to a family of specifications developed by the IEEE for wireless LAN technology.

802.11 specifies an over-the-air interface between a wireless client and a base station or between two wireless clients.

The IEEE accepted the specification in 1997.

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Bluetooth

Bluetooth is an industrial specification for wireless personal area networks (PANs).

Bluetooth provides a way to connect and exchange information between devices such as mobile phones, laptops, PCs, printers, digital cameras, and video game consoles over a secure, globally unlicensed short-range radio frequency.

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IrDA

Short for Infrared Data Association, a group of device manufacturers that developed a standard for transmitting data via infrared light waves.

Increasingly, computers and other devices (such as printers) come with IrDA ports. This enables you to transfer data from one device to another without any cables.

For example, if both your laptop computer and printer have IrDA ports, you can simply put your computer in front of the printer and output a document, without needing to connect the two with a cable.

IrDA ports support roughly the same transmission rates as traditional parallel ports.

The only restriction on their use is that the two devices must be within a few feet of each other and there must be a clear line of sight between them.

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WAP

WAP is short for the Wireless Application Protocola secure specification that allows users to access information instantly via handheld wireless devices such as mobile phones, pagers, two-way radios, smartphones and communicators.

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Intranet

An intranet is a network based on TCP/IP protocols (an internet) belonging to an organization.

accessible only by the organization's members, employees, or others with authorization.

An intranet's Web sites look and act just like any other Web sites, but the firewall surrounding an intranet fends off unauthorized access.

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Extranet

An extranet is a private network that uses Internet protocols, network connectivity, and possibly the public telecommunication system to securely share part of an organization's information or operations with suppliers, vendors, partners, customers or other businesses.

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CONNECTING NETWORKS

A hub is a central point that connects several devices in a network together

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Gateway:

hardware/software to connect different networkseg. A PC and Macintosh network

Bridge:

combination of hardware/software to connect similar networkseg. two PC networks

CONNECTING NETWORKS

Routers:Routers:

Connect several networks together and transmits data to its Connect several networks together and transmits data to its correct destination.correct destination.

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Network Architecture

Client-Server Peer-to-Peer Internet Peer-to-Peer Wireless Network

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NETWORK ARCHITECTURE

The design of computers, devices and media in a network .

Client-Server

One of more computers act as a server

The other computers on the network request for services from the server.

Peer-to-Peer

A simple inexpensive network that typically connects less than 10 computers..

Each computer has equal responsibilities and capabilities.

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NETWORK ARCHITECTURE (CONT’D)

Internet Peer-to-PeerCalled P2P, is an Internet network on which users connect directly to each other’s hard disk and exchange files over the Internet.

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Wireless Network

no physical wired connection between sender and receiver

the network is connected by radio waves and/or microwaves to maintain communications

Wireless networking utilizes specific equipment such as NICs, APs (Access Point, 访问接入点 ) and routers in place of wires (copper or optical fiber) for connectivity.

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Communications Channel

A communications channel is the transmission media on which data, instructions, or information travel, in either analog or digital form, depending on the type of communications channel.

Two examples of communications channelscable television linestelephone lines

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Communications Channel

• Basic Concepts– Bandwidth – Latency – Baseband – Broadband – Transmission Media

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Basic Concepts

• Bandwidth– the amount of data that can be transmitted

in a fixed amount of time.– For digital devices, the bandwidth is usually

expressed in bits per second (bps) or bytes per second.

– For analog devices, the bandwidth is expressed in cycles per second, or Hertz (Hz).

• Latency– the amount of time it takes a packet to

travel from source to destination.

• latency and bandwidth define the speed and capacity of a network.

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Basic Concepts

• Baseband– Baseband media is the type of media that

transmits only one signal at a time.

• Broadband– Broadband media is a type of data

transmission in which a single medium (wire) can carry several channels at once. Cable TV, for example, uses broadband transmission.

• Transmission Media– materials or substances capable of carrying

one or more signals in a communications channel.

– Transmission Media are one of two types: physical or wireless.

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Transmission Media

• Physical Transmission Media– Twisted-pair Cable– Coaxial Cable– Fiber-optic Cable

• Wireless Transmission Media– Infrared – Broadcast Radio – Cellular Radio

•Cellular Telephone •GSM •CDMA

– Microwaves – Communications Satellite

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Data Processing

• Use of networks allows an organization to process its data in a number of ways. – Centralized Data Processing

• Places everything – processing, hardware and software - in one central location.

• Very inefficient system. • Data has to be physically transported to the

computer. • Processed material has to be delivered to

users.– Distributed Data Processing

• Centralized mainframe computer system is linked with minis and micros at external locations.

• Users have control over processing local data. • Central mainframe handles applications

involving whole company.

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Exercise and Lab

Finish the CHOICE of Revision1~Revison4

Finish the Calculation questions of Revision1~Revison4

Finish the lab work of Revision1~Revison4