Using Information Technology

Telecommunications

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Telecommunications The term telecommunication means

communication at a distance. The word data refers to information presented in whatever form is agreed upon by the parties creating and using the data. Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable.

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WHAT IS A NETWORK? A network is simply two or more

computers that are linked together. The most common types of networks are:

Local Area Networks (LANS) Metropolitan Area Networks (MANS) Wide Area Networks (WANS).

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Types of NetworksMetropolitan area network (MAN) - a communications network covering a city or a suburb

Local area network (LAN) - connects computers and devices in a limited geographical area

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Types of Networks Wide area network (WAN) - a communications network that

covers a wide geographical area, such as a country or the world

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BENEFITS OF A NETWORKS Information sharing: Authorized users

can use other computers on the network to access and share information and data. This could include special group projects, databases, etc.

Hardware sharing: One device connected to a network, such as a printer or scanner, can be shared by many users.

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BENEFITS OF A NETWORKS Software sharing: Instead of purchasing

and installing a software program on each computer, it can be installed on the server. All of the users can then access the program from a single location.

Collaborative environment: Users can work together on group projects by combining the power and capabilities of diverse equipment.

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COMMUNICATIONS MEDIA Communications Channel

To transfer data from one computer to another requires some type of link through which the data can be transmitted. This link is known as the communications channel.

To send data through the channel requires some type of transmission media, which may be either physical or wireless.

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Wired Communications Channels Twisted-pair -cable - consists of two

independently insulated wires twisted around each other (least expensive type of cable—the kind that is used in many telephone systems)

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Wired Communications Channels Coaxial cable - insulated copper wire wrapped in a solid

or braided metal shield, then in an external cover (the primary type of cabling used by the cable television industry; it is more expensive than twisted pair)

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Wired Communications Channels Fiber-optic cable - dozens or hundreds of thin

strands of glass or plastic that transmit pulsating beams of light rather than electricity

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Characteristics Of Cables Twisted-pair wire

characteristics:• Slow.• Does not protect well

against electrical interference.

• Prevalent! Used extensively in telephone lines.

Coaxial cablecharacteristics:• Better than twisted-pair

wiring at resisting noise.• Carries voice & data at

faster rate than twisted-pair.

• Widely used in cable television.

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Characteristics Of Cables

Fiber-optic cable characteristics:• Unaffected by random electromagnetic

interference• Lighter and more durable than twisted-pair

& co-ax cable

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Wireless Communications Channels Infrared transmission - the transmission

of data signals using infrared-light waves

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Wireless Communications Channels Broadcast radio - a

wireless transmission medium that sends data over long distances--between regions, states, or countries

Microwave radio - transmits voice & data through the atmosphere as super-high-frequency radio waves called microwaves

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Short-Range Wireless Communications

Bluetooth - a short-range wireless digital standard aimed at linking cellphones, PDAs, computers, & peripherals up to distances of 30 feet

WiFI - a short-range wireless digital standard aimed at helping machines inside offices to communicate at high speeds and share Internet connections at distances up to 300 feet

HomeRF - a separate, incompatible standard designed to network up to 10 PCs & peripherals as far as 150 feet apart

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Factors Affecting How Data Is Transmitted Transmission rate - a function of two variables:

Frequency - the cycles of waves per second

Bandwidth - the range between the highest & lowest frequencies

Higher frequency => greater transmission rate Larger bandwidth => greater transmission rate

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Factors Affecting How Data Is Transmitted Line configurations

Point-to-point line - directly connects the sending & receiving devices

Multipoint line - a single line that interconnects several communications devices to one computer

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Factors Affecting How Data Is Transmitted Serial vs. parallel

transmission

Serial data transmission - bits are transmitted sequentially, one after the other

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Factors Affecting How Data Is Transmitted

Serial vs. parallel transmission Parallel data transmission - bits are transmitted through separate lines simultaneously

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Factors Affecting How Data Is Transmitted Direction of

transmission: simplex, half-duplex, & full-duplex

Simplex transmission - data can travel in only one direction

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Factors Affecting How Data Is Transmitted

Direction of transmission: simplex, half-duplex, & full-duplex

Half-duplex transmission - data travels in both directions but only in one direction at a time

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Factors Affecting How Data Is Transmitted

Direction of transmission: simplex, half-duplex, & full-duplex

Full-duplex transmission - data is transmitted back and forth at the same time

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Factors Affecting How Data Is Transmitted

Asynchronous transmission - data is sent one byte at a time, with each string of bits making up the byte bracketed with special control bits

Transmission mode: asynchronous vs. synchronous

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Factors Affecting How Data Is Transmitted

Synchronous transmission - data is sent in blocks, with start and stop bit patterns (synch bytes) at the beginning and end of the blocks

Transmission mode: asynchronous vs. synchronous

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Factors Affecting How Data Is TransmittedCircuit switching - transmitter has full use of the circuit until all the data has been transmitted and the circuit is terminated

Packet switching - electronic messages are divided into packets for transmission over a wide area network to their destination through the most expedient route

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Factors Affecting How Data Is Transmitted

Multiplexers: a device that merges several low-speed transmissions into one high-speed transmission.

Concentrators: collects data in a temporary storage area.

Front-end processors: a smaller computer that is connected to a larger computer and assists with communications functions.

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HOW ARE NETWORKS CATEGORIZED? Networks are usually classified

using three properties: Topology Protocol Architecture

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Topology of LANs Bus network - one in

which all communications devices are connected to a common channel

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Topology of LANs Ring network - one in

which all microcomputers and other communications devices are connected in a continuous loop

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Topology of LANs Star network - one in which all microcomputers and other

communications devices are connected to a central server

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NETWORK/COMMUNICATION PROTOCOLS Protocol - a set of

conventions governing the exchange of data between hardware and/or software components in a communications network

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Types of LANS Peer-to-peer LAN - all microcomputers on the

network communicate directly with one another without relying on a server

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Types of LANS Client/server LAN:

Clients - microcomputers that request data; and

Server - a powerful microcomputer that manages shared devices

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NETWORKING HARDWARE AND SOFTWARE

Hub – electronic device (with a number of ports) used in a LAN to link groups of computers

Repeaters (also called amplifiers) – electronic devices that receive signals and amplify and send them along the network

Routers - electronic devices used to ensure messages are sent to their intended destinations

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NETWORKING HARDWARE AND SOFTWARE

Gateway – consists of hardware and/or software that allows communications between dissimilar networks

Bridge – consists of hardware and/or software that allows communication between two similar networks

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Intranets, Extranets, & Firewalls

Intranet- an organization’s internal private network that uses the infrastructure and standards of the Internet and the WWW

Extranets - private intranets that connect not only internal personnel but also selected suppliers and other strategic parties

Firewalls - a system of hardware and software that blocks unauthorized users inside and outside the organization from entering the intranet