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Technology Guide 4. Telecommunications. Hardware Communications media Communications networks Communications processors. Communications software Data communications providers Communication protocols Communications applications. Telecommunication System.

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Technology Guide 4

Telecommunications


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Hardware

Communications media

Communications networks

Communications processors

Communications software

Data communications providers

Communication protocols

Communications applications

Telecommunication System

Atelecommunication system is a collection of compatible hardware and software arranged to communicate information from one location to another. The major components include;



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Analog signals are continuous waves that “carry” information by altering the amplitudeand frequencyof the waves.

Digital signals are discrete on-off pulses that convey information in terms of 1s and 0s, just like the central processing unit in computers.

Electronic Signals

Telecommunications media can carry two basic types of signals;


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Communication Processors

  • Modulationrefers to the conversion from digital to analog and the reverse is demodulation.

  • The device that performs these two processes is called a modem.

  • Modems are always used in pairs.

    • The unit at the sending end converts digital information into analog signals for transmission over analog lines;

    • At the receiving end, another modem converts the analog signal back into digital signals for the receiving computer.


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Communication Processors (cont.)

  • Two main alternatives to analog modems are:

    • Digital subscriber line (DSL)

    • Cable modem

  • A multiplexor is an electronic device that allows a single communications channel (e.g, a telephone circuit) to carry data transmissions simultaneously from many sources.

  • A front-end processoris a specialized computer that manages all routing communications with peripheral devices.


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Communications Media

  • Communications media (channels) refer to the physical pathway or medium for which data is communicated from one location to another.

  • There are two categories:

    • Wireline

    • Wireless


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Wireline

Twisted pair wire

Coaxial cable

Fiber optic cable

Wireless

Cellular radio

Microwave transmission

Satellite transmission

Global positioning system

Radio & Infrared light

Wireline vs. Wireless Media


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Mobile computing refers to the use of portable computer devices in multiple locations.

Personal communication service (PCS) uses lower-power, higher frequency radio waves than cellular technology. As a result, PCS cells are smaller, more numerous and closer together.

Personal digital assistants (PDAs) are small, pen-based, hand-held computers capable of digital communications transmission.

Bluetoothis a relatively new technology that allows wireless communication between mobile phones, laptops, and other portable devices.

Wireless Technologies


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Transmission Speed

  • Bandwidth refers to the range of frequencies that can be sent over a communications channel.

  • Abaud is a detectable change in a signal (i.e., a change from a positive to a negative voltage in a wire).

  • Baud rate refers to the rate at which signals can be transmitted through a communications channel.

  • Channel capacity is usually divided into three bandwidths:

    • Narrowband (e.g., telegraph lines)

    • Voiceband (e.g., telephone)

    • Broadband(e.g., microwave, cable, and fiber-optic media)


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Transmission Direction

  • Simplex data transmission uses one circuit in one direction only—similar to a doorbell, a public announcement system, or broadcast television and radio.

  • Half-duplex transmission also uses only one circuit, but it is used in both directions—one direction at a time.

  • Full-duplex transmission uses two circuits for communications—one for each direction simultaneously.

    • e.g, a common telephone


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Transmission Mode & Accuracy

  • Data transmissions may be either asynchronous or synchronous;

    • Asynchronous - only one character is transmitted or received at a time.

    • Synchronous - a group of characters is sent over a communications link in a continuous bit stream while data transfer is controlled by a timing signal initiated by the sending device.

  • Because the loss of even one bit could alter a character or control code, data transmission requires accuracy controls.

    • These controls consist of bits calledparity bits.


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Protocol

  • Protocolrefers to the set of rules and procedures governing transmission across a network.

  • The simplest protocol ispolling, where a master device polls, or contacts, each node.

  • In the token passing approach, a small data packet, called a token, is sent around the network.

  • In another approach called contention a device that wants to send a message checks the communications medium to see if it is in use.

  • The Transmission Control Protocol/Internet Protocol (TCP/IP) is a protocol for sending information across sometimes-unreliable networks.


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Communication Standards

The major types of standards are;

  • Networking standards

  • Transmission standards

  • Software standards


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Networking Standards

  • One or more protocols define precisely how software programs on different systems interact to accomplish the functions for each layer.

  • The Open Systems Interconnection (OSI)model has seven layers, each having its own well-defined function:

    Layer 1:Physical layerLayer 5: Session layer

    Layer 2: Data link layerLayer 6: Presentation layer

    Layer 3: Network layerLayer 7: Application layer

    Layer 4: Transport layer


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Transmission Standards

  • A number of network bandwidth boosters address the need for greater bandwidth on networks for advanced computing applications.

  • These include:

    • FDDI (fiber distributed data interface)

    • ATM (asynchronous transfer mode)

    • LAN switches

    • ISDN (integrated services digital network)


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An interface is a physical connection between two communications devices.

Parallel data transfer

Serial data transfer

The topology of a network is the physical layout and connectivity of a network.

Ring topology

Bus topology

Star network

Interface & Topology


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Local area networks (LAN)

Gateway, bridge, router

Network Interface Cards

Private branch exchange (PBX)

Wide area networks (WAN)

Value-added Network (VAN)

Packet Switching

Frame relay

Virtual private network (VPN)

Network Size

There are two general network sizes:


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Centralized Architecture

  • Centralized computer systems are centered around a large computer, known as the host, that provides computational power and internal storage.

  • Several devices that lack self-contained computer processors, such as “dumb” terminals and printers, are connected to the host.

  • Although mainframes have represented the dominant centralized form of computing for over 30 years, minicomputers, workstations, and powerful PCs are challenging that dominance.


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Non-centralized Computing

  • Non-centralized computing architectures are decentralized or distributed.

  • Decentralized computing breaks centralized computing into functionally equivalent parts, with each part essentially a smaller, centralized subsystem.

  • Distributed computing breaks centralized computing into many computers that may not be (and usually are not) functionally equivalent.


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Client/Server Architecture

  • The basic structure of client/server architecture is a client device(s) and a server device(s) that are distinguishable, but interact with each other.

  • In a client/server approach, the components of an application are distributed over the enterprise rather than being centrally controlled.

  • There are three application components that can be distributed:

    • the presentation component

    • the applications (or processing) logic

    • the data management component


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Client/Server Architecture (cont.)

There are five models of client/server implementation;

  • Distributed presentation

  • Remote presentation

  • Distributed function

  • Remote data management

  • Distributed data management


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Peer-to-Peer Network Architecture

  • A peer-to-peer network architecture allows two or more computers to pool their resources together.

  • There are several advantages of peer-to-peer architecture::

    • There is no need for a network administrator.

    • The network is fast and inexpensive to set up and maintain.

    • Each computer can make backup copies of its files to other computers for security.

    • It is the easiest network to build.


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Open Systems

  • Open systems provide flexibility in implementing IT solutions, optimization of computing effectiveness, and the ability to provide new levels of integrated functionality to meet user demands.

  • Connectivityis the ability of the various computer resources to communicate with each other through network devices without human intervention.

  • Open systems and connectivity have enabled networks to completely span organizations.


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Enterprise Networking

  • Portability is the ability to move applications, data, and even people from one system to another with minimal adjustments.

  • Interoperability refers to the ability of systems to work together by sharing applications, data, and computer resources.

  • Scalability refers to the ability to run applications unchanged on any open system where the hardware can range from a laptop PC to a super computer.


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