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Chapter 1
Introduction
UniMAP
EKT 440 Telecommunication Switch Networks
Communications
Communications The message (data and information) is
communicated via the signal The transmission medium “carries” the signal
Sender ReceiverSignal
Transmissionmedium
Communications ‘Discussion’
The transmission of data from one computer to another, or from one
device to another. A communications device, therefore, is any
machine that assists data transmission. For example, modems,
cables, and ports are all communications devices. Communications
software refers to programs that make it possible to transmit data.
Telecommunications
Telecommunications The electronic transmission of signals for
communications, including such means as:• Telephone
• Radio
• Television
Telecommunication medium• Anything that carries an electronic signal and interfaces
between a sending device and a receiving device
Communications and Telecommunications
• In human speech, the sender transmits a signal through the transmission medium of the air
• In telecommunications, the sender transmits a signal through the transmission medium of a cable
Schematic
Data Communications
Data communications A specialized subset of telecommunications
that refers to the electronic collection, processing, and distribution of data -- typically between computer system hardware devices
Elements of a Telecommunications System
Telecommunication devices Relay signals between computer systems and
transmission media
Schematic
Computer Network
Computer network… The communications media, devices, and
software needed to connect two or more computer systems and/or devices
Used to share hardware, programs, and databases across the organization
Fosters teamwork, innovative ideas, and new business strategies
Types of Telecommunications Media (1)
Twisted pair wire cable• Insulated pairs of wires historically used in
telephone service and to connect computer devices
Coaxial cable• Consists of an inner conductor wire
surrounded by insulation, called the dielectric
• The dielectric is surrounded by a conductive shield, which is surrounded by a non-conductive jacket. Coaxial cable has better data transmission rate than twisted pair
Twisted-pair ‘Discussion’
A type of cable that consists of two independently insulated wires
twisted around one another. One wire carries the signal while the
other wire is grounded and absorbs signal interference. Twisted-pair
cable is used by older telephone networks and is the least expensive
type of local-area network (LAN) cable. Other types of cables used
for LANs include coaxial cables and fiber optic cables.
Coaxial Cable ‘Discussion’
A type of wire that consists of a centre wire surrounded byinsulation and then a grounded shield of braided wire. The shieldminimizes electrical and radio frequency interference.
Coaxial cabling is the primary type of cabling used by the cabletelevision industry and is also widely used for computer networks.Although more expensive than standard telephone wire, it is muchless susceptible to interference and can carry much more data.Because the cable television industry has already connected millionsof homes with coaxial cable, many analysts believe that they arethe best positioned to capitalize on the much-heralded informationhighway.
Types of Telecommunications Media (2)
Fiber-optic Cable• Many extremely thin
strands of glass or plastic bound together in a sheathing which transmits signals with light beams
• Can be used for voice, data, and video
Fiber Optic ‘Discussion’ (1)
A technology that uses glass (or plastic) threads (fibers) to transmitdata. A fiber optic cable consists of a bundle of glass threads, eachof which is capable of transmitting messages modulated onto lightwaves.
Fiber optics has several advantages over traditional metalcommunications lines:
Fiber optic cables have a much greater bandwidth than metal cables. This means that they can carry more data
Fiber optic cables are less susceptible than metal cables to interference Fiber optic cables are much thinner and lighter than metal wires Data can be transmitted digitally (the natural form for computer data) rather
than analogically.
Fiber Optic ‘Discussion’ (2)
The main disadvantage of fiber optics is that the cables areexpensive to install. In addition, they are more fragile than wire andare difficult to split.
Fiber optics is a particularly popular technology for local-areanetworks. In addition, telephone companies are steadily replacingtraditional telephone lines with fiber optic cables. In the future,almost all communications will employ fiber optics.
Types of Telecommunications Media (3)
Microwave Communications• Line-of-sight devices which must be placed in
relatively high locations
• Microwave usage– Information is converted to a microwave signal, sent
through the air to a receiver, and recovered
picture
Types of Telecommunications Media (4)
Satellite transmission• Communications satellites are relay stations that
receive signals from one earth station and rebroadcast them to another
• They use microwave signals
picture
Types of Telecommunications Media (5)
Cellular transmission• Signals from cells are transmitted to a receiver and
integrated into the regular network
picture
Cellular ‘Discussion’Refers to communications systems, especially the Advance MobilePhone Service (AMPS), that divide a geographic region into sections,called cells. The purpose of this division is to make the most use outof a limited number of transmission frequencies. Each connection, orconversation, requires its own dedicated frequency, and the totalnumber of available frequencies is about 1,000. To support morethan 1,000 simultaneous conversations, cellular systems allocate aset number of frequencies for each cell. Two cells can use the samefrequency for different conversations so long as the cells are notadjacent to each other.
For digital communications, several competing cellular systems exist,including GSM and CDMA.
Types of Telecommunications Media (6)
Infrared transmission• Involves sending signals through the air via light
waves
• Requires line-of-sight and short distances (a few hundred yards)
• Used to connect various computing devices such as handheld computers
Sorry, no picture!
Terminology
Analog Signal A continuous, curving signal
Digital Signal A signal represented by bits
Modems Devices that translate data from digital to
analog and analog to digital
Analog ‘Discussion’ (1)
Almost everything in the world can be described or represented inone of two forms: analog or digital. The principal feature of analogrepresentations is that they are continuous. In contrast, digitalrepresentations consist of values measured at discrete intervals.
Digital watches are called digital because they go from one value tothe next without displaying all intermediate values. Consequently,they can display only a finite number of times of the day. Incontrast, watches with hands are analog, because the hands movecontinuously around the clock face. As the minute hand goes
Analog ‘Discussion’ (1)
around, it not only touches the numbers 1 through 12, but also the
infinite number of points in between.
Early attempts at building computers used analog techniques, but
accuracy and reliability were not good enough. Today, almost all
computers are digital.
Digital ‘Discussion’ (1)
Describes any system based on discontinuous data or events.Computers are digital machines because at their most basic levelthey can distinguish between just two values, 0 and 1, or off andon. There is no simple way to represent all the values in between,such as 0.25. All data that a computer processes must be encodeddigitally, as a series of zeroes and ones.
The opposite of digital is analog. A typical analog device is a clock inwhich the hands move continuously around the face. Such a clock iscapable of indicating every possible time of day. In contrast, a
Digital ‘Discussion’ (2)
digital clock is capable of representing only a finite number of times(every tenth of a second, for example).
In general, humans experience the world analogically. Vision, forexample, is an analog experience because we perceive infinitelysmooth gradations of shapes and colors. Most analog events,however, can be simulated digitally. Photographs in newspapers, forinstance, consist of an array of dots that are either black or white.From afar, the viewer does not see the dots (the digital form), butonly lines and shading, which appear to be continuous. Although
Digital ‘Discussion’ (3)
digital representations are approximations of analog events, they areuseful because they are relatively easy to store and manipulateelectronically. The trick is in converting from analog to digital, andback again.
This is the principle behind compact discs (CDs). The music itselfexists in an analog form, as waves in the air, but these sounds arethen translated into a digital form that is encoded onto the disk.When you play a compact disc, the CD player reads the digital data,translates it back into its original analog form, and sends it to the
Digital ‘Discussion’ (4)
amplifier and eventually the speakers.
Internally, computers are digital because they consist of discrete
units called bits that are either on or off. But by combining many
bits in complex ways, computers simulate analog events. In one
sense, this is what computer science is all about.
How a Modem Works
Modem Modulates a digital signal into an analog signal
for transmission via analog medium, then demodulates the signal into digital for receiving
picture
Modem ‘Discussion’ (1)
Acronym for modulator-demodulator. A modem is a device orprogram that enables a computer to transmit data over telephonelines. Computer information is stored digitally, whereas informationtransmitted over telephone lines is transmitted in the form of analogwaves. A modem converts between these two forms.
Fortunately, there is one standard interface for connecting externalmodems to computers called RS-232. Consequently, any externalmodem can be attached to any computer that has an RS-232 port,which almost all personal computers have. There are also modems
Modem ‘Discussion’ (2)
that come as an expansion board that you can insert into a vacant
expansion slot. These are sometimes called onboard or internal
modems.
Multiplexer
Multiplexer Allows several telecommunications signals to
be transmitted over a single communications medium at the same time
picture
Communicationslink
Multiplexor Front-endprocessor
Hostcomputer
Multiplexor ‘Discussion’
A communications device that multiplexes (combines) several signals
for transmission over a single medium. A demultiplexor completes
the process by separating multiplexed signals from a transmission
line. Frequently a multiplexor and demultiplexor are combined into a
single device capable of processing both outgoing and incoming
signals.
A multiplexor is sometimes called a mux.
Front-End Processor
Front-end processor… Special purpose computers that manage
communication to and from a computer system
picture
Incoming and outgoing jobs
Front-endprocessor
Mainsystem
Job 1
Job 2
Job 3
Job 4
Carriers and Services (1)
Carriers• Organizations that take the responsibility of ensuring telecommunications can
effectively take place between enterprises
Common carriers• Long-distance telephone companies
Value-added carriers• Companies that have developed private telecommunications systems and offer
their services for a fee
Switched lines• Lines that use switching equipment to allow one transmission device to be
connected to other transmission devices (e.g., standard telephone line)
Dedicated line• A line that provides constant connection between two points. No switching or
dialing is needed
Carriers and Services (2)
Private branch exchange (PBX) Communication system that can manage both voice and data transfer
within a location (e.g. a building) and to outside lines
Wide area telecommunication service (WATS) Billing method for heavy users of voice services
Phone and dialing services Includes automatic number identification (a.k.a. caller ID) Integration of telephones and personal computers Access code screening Call priorities One number portability (use anywhere) Intelligent dialing (auto re-dial for a busy number)
ISDN• ISDN = Integrated Services Digital Network
• Technology that uses existing common-carrier lines to simultaneously transmit voice, video, and image data in digital form
Pretty picture
Carriers and Services (3)
T1 carriers• An expensive service developed by AT&T to
increase the number of voice calls that could be handled through existing cables
Digital subscriber lines (DSL)• Uses existing phone wires going into today’s homes
and businesses to provide transmission speeds exceeding 500 Kbps at a cost of $100 - $300 per month
Carriers and Services (4)
Networks and Distributed Processing
Centralized processing Data processing that occurs in a single location or
facility Decentralized processing
Data processing that occurs when devices are placed at various remote locations
Distributed processing Data processing that occurs when computers are
placed at remote locations but are connected to each other via telecommunications devices
Network Concepts and Considerations
Network Topology A logical model that describes how networks
are structured or configured Topologies…
• Ring (see chapter 1)• Bus (see chapter 1)• Star (see chapter 1)• Hierarchical• Hybrid
Hierarchical• Uses treelike structures
with messages passed along the branches of the hierarchy
Hybrid• Network made up of
various types of topologies
Network Types
Local area network (LAN) Connects computer systems and devices in the same
geographic area (can be Ring, Bus, Hierarchical, Star, Hybrid)
Wide area network (WAN) Ties together large geographic regions using
microwave and satellite transmission or telephone lines
International network Links systems between countries
Terminal-to-Host Connection
Applications and databases reside on the same host computer
User interacts with the application using a “dumb terminal”
Hostcomputer
Target PC
“dumb terminal”
File Server Connection
Applications and databases reside on the same host computer
File server transfers data and programs to PCs on the network, where these target PCs perform most of the processing
Hostcomputer
File downloaded to user
File server
Target PC
Client/Server Connection
Applications and databases reside on specialized host computers
Servers do most or all of the processing and transmit the results to the client
Client Server
Server ServerClient
Advantages & Disadvantages of Client/Server
Advantages Reduced cost potential Improved Performance Increased Security
Disadvantages Increased cost potential Loss of control Complex multi-vendor
environment
Communications Software and Protocols (1)
Communications software• Provides error checking, message formatting, communications
logs, data security and privacy, and translation capabilities for networks
Network operating system (NOS)• Systems software that controls the computer systems and
devices on a network and allows them to communicate with each other
Network management software• Enables a manager on a networked desktop to monitor the use
of individual computers and shared hardware, scan for viruses, and ensure compliance with software licenses
Communications Software and Protocols (2)
Protocol• Rules that ensure communications among
computers of different types and from different manufacturers.
Communications Software and Protocols (3)
Open Systems Interconnection (OSI) Model Serves as a standard model for network architectures
and is endorsed by the International Standards Committee
Communication functions are represented in seven layers to promote the development of modular networks. Designed to permit communication among different computers from different operating systems
Seven layers (see figure 6.20)
Communications Software and Protocols (4)
TCP/IP• TCP/IP = Transmission Control Protocol/Internet Protocol
Standard originally developed by the U.S. government to link defense research agencies; it is the primary communication protocol of the Internet
Systems Network Architecture (SNA)• IBM communication protocol
Ethernet• Protocol standard developed forLANs using a bus topology
X.400 and X.500• An international standard for message handling and network
directories
Bridges, Routers,Gateways and Switches
Bridge• Connects two or more networks, with the same protocol, at the
media control portions of the data link layer
Router• Operates at the network level of the OSI model and features
more sophisticated addressing software than bridges. Can determine preferred paths
Gateway• Operates at or above the OSI transport layer and links LANs or
networks that employ different architectures and use dissimilar protocols
Switch• Routes or switches data to its destination
Schematic
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Application
Presentation
Session
Transport
Network
Data link
Physical
Machine#1
Machine#2
Machine#3
Gatewaybox
Machine#4
Bridgebox
Routerbox
Media
Telecommunications Applications (1)
Linking personal computers to mainframe computers Download and upload information
Voice mail Enables users to leave, receive, and store verbal
messages for and from other users Electronic mail (e-mail)
Enables a sender to connect a computer to a network, type messages, and send it to another person on the network
Telecommunications Applications (2)
Electronic software distribution• Involves installing software on a file server for users to share by
signing onto the network and requesting that the software be downloaded onto their computers over a network
Electronic document distribution• Transporting documents -- such as sales reports, policy manuals,
and advertising brochures -- over communications lines and networks
Telecommuting• Enables employees to work away from the office using personal
computers and networks to communicate via electronic mail with other workers and to pick up and deliver results
Telecommunications Applications (3)
Videoconferencing Allows participants to conduct long-distance
meetings “face to face” while eliminating
picture
Telecommunications Applications (4)
Electronic Data Interchange (EDI)• Uses network systems and follows standards and
procedures that allow output from one system to be processed directly as input to other systems, without human intervention
Pretty picture
EDI link
EDI link EDI link
Vendor Customer
Vendor Customer
Third-partyclearing house
(a)
(b)
Telecommunications Applications (5)
Public network services Services that give personal computer users access to
vast databases and other services, usually for an initial fee plus usage fees
Specialized and regional information services Specialized electronic bulletin boards and e-mail
services targeting particular interests.
Distance learning Use of telecommunications to extend the classroom
End of Chapter
Chapter 1