Telecommunication and Telecommunication and NetworksNetworks

Telecommunications and Networks, describes basic concepts and components of networks used for data communications.

Communications is defined as the transmission of a signal over a medium from a sender to a receiver.

CommunicationsCommunications

Communication FlowCommunication Flow

Synchronous communicationSynchronous communication

Asynchronous communicationAsynchronous communication

Synchronous CommunicationSynchronous Communication

In synchronous communication, the receiver gets the message immediately.

Telephone conversations are examples of synchronous communication

Asynchronous CommunicationAsynchronous Communication

asynchronous communication, the receiver gets the message at a late time – possibly even days after the message is sent.

Sending a letter is an example of asynchronous communication, as is e-mail.

TelecommunicationsTelecommunications

TelecommunicationsTelecommunications

TelecommunicationsTelecommunications is the electronic is the electronic communication of signals, such as communication of signals, such as telephone, radio and television.telephone, radio and television.

Data communications is a subset of Data communications is a subset of telecommunications referring to the telecommunications referring to the electronic collection, processing, & electronic collection, processing, & distribution of data.distribution of data.

Telecommunications MediaTelecommunications Media

Bandwidth Bandwidth The range of frequencies that an electronic The range of frequencies that an electronic

signal occupies on a given transmission signal occupies on a given transmission medium. medium.

BroadbandBroadband Telecommunications in which a wide band of Telecommunications in which a wide band of

frequencies is available to transmit frequencies is available to transmit information, allowing more information to be information, allowing more information to be transmitted in a given amount of time.transmitted in a given amount of time.

Data Transmission SpeedsData Transmission Speeds

Measured in bits per second (bps)Measured in bits per second (bps)Kilobits per second (kbps)Kilobits per second (kbps)Megabits per second (Mbps)Megabits per second (Mbps)Gigabits per second (Gbps)Gigabits per second (Gbps)

Data communications is characterized by Data communications is characterized by the speed at which the data is sent, the speed at which the data is sent, measured in bits per second. The most measured in bits per second. The most common data transmission speeds range common data transmission speeds range from thousands to millions of bits per from thousands to millions of bits per second, or kilobits to megabits per second. second, or kilobits to megabits per second. Some networks can support transmission Some networks can support transmission of billions of bits, or gigabits, per second.of billions of bits, or gigabits, per second.

Computer NetworksComputer Networks

Telecommunications mediaTelecommunications media

Telecommunications devicesTelecommunications devices

SoftwareSoftware

Hardware devicesHardware devices

Types of MediaTypes of MediaTwisted-PairTwisted-Pair

Coaxial CableCoaxial Cable

Fiber-Optic CableFiber-Optic Cable

Microwave TransmissionMicrowave Transmission

The first 3 types of media – twisted pair, The first 3 types of media – twisted pair, coaxial cable, and fiber optic cable – are coaxial cable, and fiber optic cable – are usually referred to as usually referred to as guided or conducted guided or conducted media.media. That is, a signal is conducted over That is, a signal is conducted over a physical medium. a physical medium.

Microwave and other forms of wireless Microwave and other forms of wireless transmission are called broadcast media. transmission are called broadcast media.

Twisted-Pair Wire CableTwisted-Pair Wire Cable

Twisted-Pair Wire CableTwisted-Pair Wire Cable

consisted of pairs of twisted copper wireconsisted of pairs of twisted copper wire

used for both analogue and digital transmissionused for both analogue and digital transmission

low in costlow in cost

low in transmission speedlow in transmission speed

Twisted pair cabling is made of pairs of copper wires twisted together. Twisted pair is used for the phone connection to your house. In networking it is common to see cable consisting of 4 pairs of wires. Each pair is twisted together to reduce electrical interference between neighboring pairs, or crosstalk. The more twists there are per foot, the less interference there will be. Twisted pair is classified by the number of twists per foot. Data grade cable has more twists per foot than does voice grade cable.

Shielded twisted pair cabling includes additional shielding against external electro-magnetic interference. Unshielded twisted pair, although it doesn’t have the extra shielding, is used more often because of its lower costs and greater practicality.

Coaxial CableCoaxial Cable

Coaxial CableCoaxial Cable

A thick insulated copper wire A thick insulated copper wire

Can transmit large volumes of data quickly Can transmit large volumes of data quickly

Faster and more interference free mediumFaster and more interference free medium

Speed up to 200MB per secondSpeed up to 200MB per second

Cannot support analogue phone Cannot support analogue phone

conversations conversations

Like twisted pair, coaxial cable, or “co-ax”, is also made from copper. However, because of extra shielding and insulation, coax has less interference, and therefore a higher capacity, or bandwidth, than does twisted pair. Data can be sent over coax at about 500 Mbps, whereas data transmission speeds over twisted pair for long distances are typically well below that, although in a local area network fast speeds can be attained using twisted pair.

A type of coaxial cable is used for cable TV to your home. Cable modems can be used for Internet access several hundreds as times as fast as a modem and dial-up phone line.

Fiber Optic CableFiber Optic Cable

Fiber optic cableFiber optic cable

Consists of strands of clear glass fiberConsists of strands of clear glass fiber

Has the thickness of a human hairHas the thickness of a human hair

Data are transformed into pulses of lightData are transformed into pulses of light

Rate 500kb – several trillion bit per secondRate 500kb – several trillion bit per second

Fiber optic cableFiber optic cable

Faster lighter and more durable than wire Faster lighter and more durable than wire

mediamedia

Suitable to transfer large volumes of data Suitable to transfer large volumes of data

More expensiveMore expensive

Fiber optic cableFiber optic cable

Difficult to work withDifficult to work with

Harder to installHarder to install

Used for backbone cabling Used for backbone cabling that handle the major trafficthat handle the major traffic

a primary patha primary path

No delays and no degradation in qualityNo delays and no degradation in quality

Unlike twisted pair and coax, fiber optic cable is made of thin filaments of glass or plastic, not of copper wire. Whereas a data signal travels over twisted pair or cable as electricity, signals are transmitted as light pulses over fiber. Lasers or LCDs produce the light. A thin coating, called cladding, prevents the light from leaving the strand. Also unlike copper media, fiber is not vulnerable to electro-magnetic interference.

Fiber has a much higher bandwidth than does copper media – that is, it can carry more data faster. Fiber can have a capacity of billions of bits per second. Fiber is also the most secure medium around today. The biggest drawback of fiber is that labor costs to install and repair fiber are very high.

Microwave Microwave TransmissionTransmission

MicrowaveMicrowave

High frequency radio signals are transmitted High frequency radio signals are transmitted trough the atmosphere from one terrestrial trough the atmosphere from one terrestrial transmission station to anothertransmission station to another

A high volumeA high volume

long distancelong distance

point – to – point transmission methodpoint – to – point transmission method

The expense of physical media can be great. Whereas broadcast media, such as microwave, don’t require the purchase of physical media, the hardware required is more expensive. Microwave is a high frequency radio signal.

In terrestrial microwave, a signal travels directly between microwave transmission towers. This requires an unobstructed straight path between towers. Also, due to the curvature of the earth, towers must be spaced about 30 miles apart.

Satellite TransmissionSatellite Transmission

Satellite transmission involves sending a signal from a microwave tower to the satellite, which is basically a microwave station, then back to another microwave tower.

Although this eliminates the need for a line-of- sight between towers, the delays to upload and download the signal often make satellite transmission impractical for sending signals short distance.

Wireless transmissionWireless transmission

Sends signals through air or spaceSends signals through air or space

Technologies includeTechnologies include microwave transmissionmicrowave transmission communication satellitescommunication satellites pagerspagers cellular phonescellular phones smart phonessmart phones PDAsPDAs

Infrared TransmissionInfrared Transmission

Line of sightLine of sight

Short distancesShort distances

Infrared transmission can be used to send data short distances, for example, from a handheld computer to a desktop or a printer. Infrared transmission can also be used to connect peripherals, such as a mouse, to a computer.

Telecommunications DevicesTelecommunications Devices

Telecommunications devices are Telecommunications devices are hardware that make an electronic hardware that make an electronic transmission occur or make it more transmission occur or make it more efficient.efficient.

Modems, multiplexers, and front-end Modems, multiplexers, and front-end processors are examples of processors are examples of telecommunications devices.telecommunications devices.

ModemsModems

Analog signals: continuousAnalog signals: continuous

Digital signals: discreteDigital signals: discrete

Modulation: translating digital data to Modulation: translating digital data to analoganalog

Demodulation: translating analog data to Demodulation: translating analog data to digitaldigital

Modems modulate & demodulate dataModems modulate & demodulate data

Often, data is sent over the regular Often, data is sent over the regular telephone network, which transmits analog telephone network, which transmits analog signals. signals.

An analog signal is a continuous signal; An analog signal is a continuous signal; the transmission line varies smoothly the transmission line varies smoothly among an infinite number of states. among an infinite number of states.

Analog waves can carry a continuous Analog waves can carry a continuous range of datarange of data

computers produce digital signals. Digital computers produce digital signals. Digital signals send discrete pulses and represent signals send discrete pulses and represent a limited number of states.a limited number of states.

In the case of a computer, two states are In the case of a computer, two states are represented.represented.

In order to send a digital signal over an In order to send a digital signal over an analog line, the signal must first be analog line, the signal must first be modulated, or changed to a form that can modulated, or changed to a form that can be carried over an analog line. When the be carried over an analog line. When the signal is received, it must be demodulated signal is received, it must be demodulated so the computer can understand it. so the computer can understand it.

This is what a modem does.This is what a modem does.

MultiplexersMultiplexers

MultiplexersMultiplexers are devices that combine are devices that combine signals from several computers to allow signals from several computers to allow them to be sent over a single transmission them to be sent over a single transmission line.line.

Networks & Distributed Networks & Distributed ProcessingProcessing

Telecommunications networks are Telecommunications networks are becoming increasingly important since becoming increasingly important since they allow work to be done wherever and they allow work to be done wherever and whenever it is most advantageous. Data, whenever it is most advantageous. Data, software, hardware, and other resources software, hardware, and other resources are becoming ubiquitous – that is, easily are becoming ubiquitous – that is, easily accessible by anyone, anytime, any place. accessible by anyone, anytime, any place.

Basic Processing StrategiesBasic Processing Strategies

Centralized processingCentralized processing

Decentralized processingDecentralized processing

Distributed processingDistributed processing

There are 3 basic processing strategies when There are 3 basic processing strategies when more than 2 computer systems are used.more than 2 computer systems are used.

In centralized processingIn centralized processing, all processing is , all processing is done at one location. This is the easiest done at one location. This is the easiest strategy for the IS department to control and is strategy for the IS department to control and is appropriate when an enterprise needs a high appropriate when an enterprise needs a high level of security.level of security.

In decentralized computingIn decentralized computing, different locations , different locations have their own processing devices. Devices at have their own processing devices. Devices at different locations aren’t connected together. different locations aren’t connected together. This strategy works well when there are This strategy works well when there are independent operating units and no data independent operating units and no data interchange between units.interchange between units.

In distributed processingIn distributed processing, computers at , computers at different locations are connected by a different locations are connected by a communications network. Data and processing communications network. Data and processing are located where it is most efficient and are located where it is most efficient and effective. For example, data and programs used effective. For example, data and programs used most by the Miami office would be located in most by the Miami office would be located in Miami, and those used most by the Boston office Miami, and those used most by the Boston office would be in Boston. Users at both locations would be in Boston. Users at both locations could access data and programs at the other could access data and programs at the other site when needed.site when needed.

Network Concepts & Network Concepts & ConsiderationsConsiderations

Network topologyNetwork topology

Network typesNetwork types Local Area NetworksLocal Area Networks Wide Area NetworksWide Area Networks International networksInternational networks Home & small business networksHome & small business networks

Network TopologyNetwork Topology

Network topology describes how a Network topology describes how a network is logically organized – that is, network is logically organized – that is, how the data flows in the network. how the data flows in the network. Depending on the distance between nodes Depending on the distance between nodes and the services provided, networks may and the services provided, networks may be classified as local area networks or be classified as local area networks or wide area networks.wide area networks.

Network TopologiesNetwork TopologiesBusBus

A bus network contains devices connected A bus network contains devices connected directly in a straight line. Each device can directly in a straight line. Each device can communicate directly with every other communicate directly with every other device one the network.device one the network.

RingRing

In a ring network, devices are connected In a ring network, devices are connected in a ring and message are routed around in a ring and message are routed around the ring from one device to the next.the ring from one device to the next.

In bus and ring topologies, there is no In bus and ring topologies, there is no central coordinating computer.central coordinating computer.

StarStar

A star network has a central, coordinating A star network has a central, coordinating device; each computer on the network is device; each computer on the network is directly attached only to the central device. directly attached only to the central device. The central device is the vulnerability of The central device is the vulnerability of the network – it can become a bottleneck the network – it can become a bottleneck under heavy traffic and the whole network under heavy traffic and the whole network fails if it fails.fails if it fails.

Network TypesNetwork Types

Logical Area Network (LAN)Logical Area Network (LAN)

Limited geographical areaLimited geographical area Any topology possibleAny topology possible Network Interface Card (NIC)Network Interface Card (NIC) DesignsDesigns

Peer-to-peerPeer-to-peer

Client-serverClient-serverWide Area Network (WAN)Wide Area Network (WAN)

LANLAN

Local Area Networks connect processing Local Area Networks connect processing devices within a limited geographic area devices within a limited geographic area and do not usually use common carrier and do not usually use common carrier facilities.facilities.

Devices are attached to the media using Devices are attached to the media using network interface cards, also called network interface cards, also called network adaptersnetwork adapters..

WANWAN

Wide Area Networks connect devices over Wide Area Networks connect devices over large geographic distances using common large geographic distances using common carrier facilities. Companies may use wide carrier facilities. Companies may use wide area networks provided by others, such as area networks provided by others, such as AT&T long distance service or may deploy AT&T long distance service or may deploy their own WAN using enterprise facilities their own WAN using enterprise facilities along with common carrier facilities.along with common carrier facilities.