Komputer Telecommunications Network

Telecommunications & Networks Overview of Communication

Communications is the transmission of a signal by way of a medium from a sender to a receiver.

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Telecommunications Electronic transmission of signals for communications Telephone Radio Television

Lessens barriers of time and distance

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Telecommunications Data communications Specialized subset of telecommunications Includes the electronic collection, processing, and distribution of data

Telecommunications media Anything that carries an electronic signal and interfaces between a sending device and a receiving device

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Elements of a Telecommunications System

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Analog and Digital Signals Analog Continuous fluctuations over time between high and low voltage

Digital A discrete voltage state

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Analog and Digital Signals

Analog signal Digital signal

Fig. 6.4

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Analog Waves Frequency The number of times per second a continuous wave completes one cycle

Amplitude The difference of the extremes from the midpoint in a cycle

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Basic Modulation Techniques Amplitude modulation (AM) Converts digital data to analog signals using a single frequency carrier signal High-amplitude wave denotes a binary 1 Low-amplitude wave denotes a binary 0

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Basic Modulation Techniques Frequency modulation (FM) Uses a constant amplitude carrier signal and two frequencies to distinguish between 1 and 0

Phase modulation Uses a phase shift at transition points in the carrier frequency to represent 1 or 0

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Communications Speed Bits per second (bps) Number of bits that can be transferred in one second

Bandwidth Range of signal frequencies that can be sent over a medium at the same time

Broadband Bandwidth of 256,000 to 1 million bps

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Types of Communications Media Twisted wire cable Coaxial cable Fiber-optic cable Microwave transmission Cellular transmission Infrared transmission

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Twisted Wire Cable A cable consisting of pairs of twisted wires The twist helps the signal from “bleeding” into the next pair

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Coaxial Cable Inner conductor wire surrounded by insulation, called the dielectric

Dielectric is surrounded by a conductive shield, which is in turn covered by a layer of nonconductive insulation, called the jacket

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Fiber-Optic Cable Consists of many extremely thin strands of glass or plastic bound together in a sheathing

Transmits signals with light beams

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Wireless Transmission Microwave: Terrestrial Microwave: Satellite Cellular PCS

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Telecommunications Devices Modems Fax modems Special-purpose modems Multiplexers Communications processors

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How a Modem Works

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Multiplexers Allow several telecommunication signals to be transmitted over a single communications medium concurrently Time division multiplexer (TDM)

Multiple incoming signals are sliced into small time intervals

Frequency division multiplexer(FDM) Incoming signals are placed on different frequency ranges

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Time Division and Frequency Division Multiplexers

[Figure 6.14]

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Communications Processors Called front-end processors because they are in front of and before the main system CPU Incoming and outgoing jobs

[Figure 6.15]

Main system

Front-end processor

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Telecommunications Carriers and Services Common carriers Long-distance telephone companies

Value-added carriers Companies that have developed private telecommunications systems and offer their services for a fee

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Telecommunications Carriers and Services Switched line Standard telephone line that uses switching equipment to allow one transmission device to be connected to others

Dedicated line Provides a constant connection between two points Also called a leased line

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Telecommunications Carriers and Services Private branch exchange (PBX) Manages both voice and data transfer within a building and to outside lines

Wide area telephone services (WATS) A billing method for heavy users of voiceband media

Phone and dialing services Additional services from the common carriers (i.e. ANI)

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Telecommunications Carriers and Services Integrated services digital network (ISDN) Technology that uses existing common-carrier lines to simultaneously transmit voice, video, and image data in digital form

Digital subscriber line (DSL) Businesses/homes that have a DSL over existing phone wires can use a special modem that transmits up to 768 Kbps

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Telecommunications Act of 1996 Completely rewrites the 62-year-old Communications Act Goal: To promote competition and eliminate monopolies for a wide range of communication services May cause profound changes in U.S. communications that can lead to a complete renovation in the way information is delivered to consumers

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Global Telecommunications One of the largest and fastest growing sectors of the global economies

Criticality of implementing and managing global networks

Increase of international acquisitions and mergers Need to compete on a global basis

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Computer Network Includes communications media, devices, and software needed to connect two or more computer systems and/or devices Benefits of a Network

Can turn a company into an agile, powerful and creative organization, giving it long-term competitive advantage Can be used to share hardware, programs, and databases across the organization

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Basic Data Processing Strategies Centralized processing All processing occurs in a single location

Decentralized processing Processing devices are placed at various remote locations

Distributed processing Computers at remote locations are connected to each other via telecommunications devices

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Network Concepts and Considerations Network topology Logical models that describe how networks are structured or configured

Star network A network that has a central hub or computer system

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Four Basic Types of Network Topology

(a) ring

[Figure 6.17]

(c) hierarchical

(b) bus

(d) star

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Types of Networks Local area networks (LAN) Connect computer systems and devices within the same geographical area

Regional networks Tie regional areas together via telecommunications systems

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Types of Networks  Wide area networks (WAN)  Tie large geographic regions together using microwave and satellite transmission or telephone lines

 Private WANs  Computer equipment owned by users and data communications equipment provided by a common carrier

 Value-added networks (VAN)  Offer services in addition to those offered by a traditional network (e.g., CompuServe)

 International networks  Link system together between countries Telecommunications & Networks :Page 32/54

Terminal-to-Host “Dumb” terminal

Fig 6.20

Applications and databases reside on the same host computer User interacts with the application using a “dumb” terminal

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LANs and WANs

[Figure 6.18]

A Typical LAN in a BUS Topology

[Figure 6.19]

A Wide Area Network Telecommunications & Networks :Page 34/54

File Server

Fig 6.21

 Applications and databases reside on the same host computer  File server transfers data and programs to PCs on the network, which do the processing Telecommunications & Networks :Page 35/54

Client/Server

Fig 6.22

 Applications and databases reside on specialized host computers  Servers do most or all of the processing and transmit the results to the client Telecommunications & Networks :Page 36/54

The Client/Server Approach Advantages  Cost potential Improved performance Increased security

Disadvantages Increased cost potential Loss of control Complex multivendor environment

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Functions of Communications Software Error checking Message formatting Communications logs Data security and privacy Translation capabilities for networks

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Communications Software Network operating systems Systems software that controls the computer systems and devices on a network and allows them to communicate with each other

Network management software Software tools and utilities available for managing networks

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Communications Protocols  Open systems interconnection (OSI)  A protocol (or standard) endorsed by the International Standards Committee

 TCP/IP  Developed by the U.S. government to link its defense research agencies

 SNA  IBM’s communications protocol

 Ethernet  A popular protocol often used with local area networks

 Other protocols

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Bridges, Routers, and Gateways Bridge Connects two or more networks

Router Features more sophisticated addressing software than bridges

Gateway Links LANs or networks that employ different higher-level protocols

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Bridges, Routers, & Gateways

[Figure 6.24]

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Coordinating Communications & Networks

Polling A procedure in which the main computer checks each device one at a time to see if there are any messages waiting to be communicated to other network devices

Token passing A technique in which an electronic “token” is passed from one device to another

Contention A procedure in which a device checks to see if a message is currently being transmitted Telecommunications & Networks :Page 43/54

Data Transfer Modes Packet switching Communications process that divides electronic messages into small segments (data packets)

Frame relay Uses wideband communications media and high speed switching devices

Voice-over frame relay Moves voice traffic onto frame relay to bypass the public telephone network

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Data Transfer Modes Asynchronous transfer mode (ATM) A high-speed network technology that provides transport for voice, video, text, and other multimedia data

Fiber distributed data interface (FDDI) Designed specifically to serve the needs of high-performance, mission-critical LAN applications

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Telecommunications Applications Links between PCs and mainframes Facilitates the upload or download of data

Voice storage and forwarding Sometimes called voice mail Allows users to leave, receive, and store verbal messages for and from people around the world

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Telecommunications Applications Electronic mail Users connected to a network can send messages to others by computer

Electronic document distribution Involves transporting documents over communications lines and networks

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Telecommunications Applications Electronic software distribution Involves installing software on a file server for users to share by signing onto the network and downloading the software onto their computers over the network

Telecommuting Working at home on a PC and communicating with the central office or other workers via networks

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Telecommunications Applications Teleconferencing Allows groups to have conferences in one connected voice phone call

Videoconferencing An extension of teleconferencing that combines voice, video, and audio transmission

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Telecommunications Applications  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

 [Figure 6.27]

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Telecommunications Applications  Public network services  Give PC users access to vast databases and other services, usually for an initial fee plus usage fees

[Figure 6.28]

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Telecommunications Applications Specialized information systems Include legal, patent, and technical information

Regional information systems Include local electronic bulletin boards and electronic mail facilities that offer information regarding local club, school, and government activities

Distance learning Extends the classroom by using telecommunications

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Network Design Considerations Reliability Security Response time Privacy issues Vendor services and support Company support

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Communications Audits Purpose:

To make sure the communications system is operating as intended

Types of communications audits: Walk-thorough Software check Network check Policy and procedures Program and database check Telecommunications & Networks :Page 54/54

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