Lecture Sheet1

NETWORKS AND TELECOMMUNICATIONS

DEFINITION Telecommunications can be defined as communication of information by electronic means, usually over some distance. We are currently in the middle of a telecommunications revolution that has two components:

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Rapid changes in the technology of communications and Equally important changes in the ownership, control, and marketing of telecommunications services.

Today’s managers need to understand the capabilities, costs, and benefits of alternative communications technologies and how to maximize their benefits for their organizations. USE OF COMPUTER NETWORKS Computer networks provide many benefits. Major uses of computer networks are:  Simultaneous access to programs and data.

 Sharing peripheral devices like printers, scanners etc.  Personal communications using e-mail.  Making backup of information.  Aiding communication by teleconferencing and video-conferencing.  Protecting information by account name and password. COMPONENTS AND FUNCTIONS OF A TELECOMMUNICATIONS SYSTEM A telecommunications system is a collection of compatible hardware and software arranged to communicate information from one location to another. Following figure illustrates the components of a typical telecommunications system. Telecommunications systems can transmit text, graphic images, voice, or video information. COMPONENTS OF TELECOMMUNICATIONS SYSTEM The essential components of a telecommunications system are these: 1.

Computers to process information.

2. 3.

Terminals or any input/output devices that send or receive data.

4.

Communications processors like modems, multiplexers, controllers, and front-end processors, which provide support functions for data transmission and reception. Communications software that controls input and output activities and manages other functions of the communications network.

5.

Communications channels, the links by which data or voice are transmitted between sending and receiving devices in a network. Communications channels use various communications media, like telephone lines, fiber-optic cables, coaxial cables, and wireless transmission.

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FUNCTIONS OF TELECOMMUNICATIONS SYSTEMS In order to send and receive information from one place to another, a telecommunications system must perform a number of separate functions. These functions are largely invisible to the people using the system. As outlined in the following table, a telecommunications system transmits information, establishes the interface between the sender and the receiver, routes messages along the most efficient paths, performs elementary processing of the information to ensure that the right message gets to the right receiver, performs editorial tasks on the data (such as checking for errors and rearranging the format), and converts messages from one speed (say, the speed of a computer) into the speed of a communications line or from one format to another. Lastly, the telecommunications system controls the flow of information. Many of these tasks are accomplished by computer. Functions of Telecommunications Functions

Definition

Transmission

Media, networks, and path

Interface

Path – sender – receiver

Routing

Choosing the most efficient path

Processing

Getting the right message to the right receiver

Editorial

Checking for errors, formats, and editing

Conversion

Changing speeds and codes from one device to another

Control

Routine messages, polling receivers, providing network structure maintenance

PROTOCOL A telecommunications network typically contains diverse hardware and software components that need to work together to transmit information. Different components in a network can communicate by adhering to a common set of rules that enable them to “talk” to each other. This set of rules and procedures governing transmission between two points in a network is called a protocol. Each device in a network must be able to interpret the other device’s protocol. The principal functions of protocols in a telecommunications network are

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To identify each device in the communication path,

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To perform recovery when errors occur.

To secure the attention of the other device, To verify correct receipt of the transmitted message, To verify that a message requires retransmission because it cannot be correctly interpreted, and

TYPES OF SIGNALS: ANALOG AND DIGITAL Information travels through a telecommunications system in the form of electromagnetic signals. Signals are represented in two ways: 1. Analog Signal 2. Digital Signal Analog Signal: An analog signal is represented by a continuous waveform that passes through a communications medium. Analog signals are used to handle voice communications and to reflect variations in pitch. Digital Signals: A digital signal is a discrete rather than a continuous waveform. It transmits data coded into two discrete states: 1-bits and 0-bits which are represented as on-off electrical pulses. Most computers communicate with digital signals, as do many local telephone companies and some larger networks. But if a telecommunications system, such as a traditional telephone network, is set up to process analog signals – the receivers, transmitters, amplifiers, and so forth – a digital signal cannot be processed without some alterations. All digital signals must be translated into analog signals before they can be transmitted in an analog system. The device that performs this translation is called a modem. A model translates the digital signals of a computer into analog form for transmission over ordinary telephone lines, or it translates analog signals back into digital form for reception by a computer.

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TYPES OF COMMUNICATION CHANNELS Communications channels are the means by which data are transmitted from one dive in a network to another. A channel can utilize different kinds of telecommunications transmission media: twisted wire, coaxial cable, fiber optics, terrestrial microwave, satellite, and wireless transmission. Each has certain advantages and limitations. High-speed transmission media are more expensive in general, but they can handle higher volumes. For instance, the cost per bit of data can be lower via satellite link than via leased telephone line if a firm uses the satellite link 100 percent of the time. There is also a wide range of speeds possible for any given medium depending on the software and hardware configuration. Twisted Wire Ordinary telephone wire, consisting of copper wire twisted into pair (twisted-pair wire), is the most widely used media for telecommunications. These lines are used in established communications networks throughout the world for both voice and data transmission. Thus, twisted-pair wiring is used extensively in home and office telephone systems and many local area networks. Coaxial Cable Coaxial cable, like that used for cable television, consists of thickly insulated copper wire, which can transmit a larger volume of data than twisted wire can. It is often used in place of twisted wire for important links in a telecommunications network because it is a faster, more interference-free transmission medium, with speeds of up to 200 megabits per second. However, coaxial cable is thick, is hard to wire in many buildings, and cannot support analog phone conversations. It must be moved when computers and other devices are moved. Fiber Optic Cable Fiber optic cable consists of thousands of strands of clear glass fiber, the thickness of a human hair, which are bound into cables. Data are transformed into pulses of light, which are sent through the fiber optic cable by a laser device at a rate of 500 kilobits to several billion bits per second. On the one hand, fiber optic cable is considerably faster, lighter, and more durable than wire media and is well suited to systems requiring transfers of large volumes of data. On the other hand, fiber optic is more difficult to work with, more expensive, and harder to install. It is best used as the backbone of a network and not for connecting isolated devices to a backbone. In most networks, fiber optic cable is used as the high-speed trunk line, while twisted wire and coaxial cable are used to connect the trunk line to individual devices. Wireless Transmission Wireless transmission that sends signals through air or space without any physical tether has emerged as an important alternative to tethered transmission channels such as twisted wire, coaxial cable, and fiber optics. Today, common uses of wireless data transmission include pagers, cellular telephones, microwave transmissions, communications satellites, mobile data networks, personal communications services, personal digital assistants, and even television remote controls. The wireless transmission medium is the electromagnetic spectrum. Some types of wireless transmission, such as microwave or infrared, by nature occupy specific spectrum frequency ranges (measured in megahertz). Other types of wireless transmissions are actually functional uses, such as cellular telephones and paging devices that have been assigned a specific range of frequencies by national regulatory agencies and international agreements. Each frequency range has its own strengths and limitations, and these have helped determine the specific functions or data communications niche assigned to it. Microwave Systems: Microwave systems, both terrestrial and celestial, transmit high-frequency radio signals through the atmosphere and are widely used for high-volume, long-distance, point-topoint communication. Because microwave signals follow a straight line and do not bend with the curvature of the earth, long-distance terrestrial transmission systems require that transmission stations be positioned 25 to 30 miles apart, adding to the expense of microwave. Satellite: Transmission of data using orbiting satellites to serve as relay stations for transmitting microwave signals over very long distances. Low-orbit satellites - Satellites that travel much closer to the earth than traditional satellites and so are able to pick up signals from weak transmitters while consuming less power. Paging Systems: A wireless transmission technology in which the pager beeps when the user receives a message; used to transmit short alphanumeric messages. Cellular Telephone: Device that transmits voice or data, using radio waves to communicate with radio antennas placed within adjacent geographic areas called cells.

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Personal Digital Assistants (PDA): Small, pen-based, hand-held computers with build-in wireless telecommunications capable of entirely digital communications transmission. CHARACTERISTICS OF COMMUNICATIONS CHANNELS The characteristics of the communications channel help determine the efficiency and capabilities of a telecommunications system. These characteristics include the speed of transmission, the direction in which signals may travel, and the mode of transmission. Transmission Speed The total amount of information that can be transmitted through any telecommunications channel is measured in bits per second (BPS). Sometimes this is refereed to as the baud rate. Baud is a change in signal from positive to negative or vice versa that is used as a measure of transmission speed. Bandwidth is the capacity of a communications channel as measured by the difference between the highest and lowest frequencies that can be transmitted by that channel.

Transmission Modes There are several conventions for transmitting signals; these methods are necessary for devices to communicate when a character begins or ends. Asynchronous transmission (often referred to as start – stop transmission) transmits one character at a time over a line, each character framed by control bits – a start bit, one or two stop bits, and a parity bit. Asynchronous transmission is used for low – speed transmission. Synchronous transmission transmits groups of characters simultaneously, with the beginning and ending of a block of characters determined by the timing circuitry of the sending and receiving devices. Synchronous transmission is used for transmitting large volumes of data at high speeds.

Transmission Direction Transmission must also consider the direction of data flow over a telecommunications network. Simplex: In simplex transmission, data can travel in only one direction at all times. Half-duplex transmission: In half-duplex transmission, data can travel in two directions, but in only one direction at one time. Full-duplex transmission: In full-duplex transmission, data is sent in both directions simultaneously, similar to two trains passing in opposite directions on side-by-side tracks.

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COMMUNICATIONS PROCESSORS Communications processors, such as front-end processors, concentrators, controllers, multiplexers, and modems, support data transmission and reception in telecommunications network. Front-End Processor The front-end processor is a small computer (often a programmable minicomputer) dedicated to communications management and is attached to the main, or host, computer in a computer system. The front-end processor performs special processing related to communications such as error control, formatting, editing, control-ling, routing, and speed and signal conversion. It takes some of the load off the host computer. The front-end processor is largely responsible for collecting and processing input and output data to and from terminals and grouping characters into complete messages for submission to the CPU of the host computer. Concentrator A concentrator is a programmable telecommunications computer that collects and temporarily stores messages from terminals until enough messages are ready to be sent economically. The concentrator then “bursts” signals to the host computer. Controller A controller, which is often a specialized minicomputer, supervises communications traffic between the CPU and peripheral devices such as terminals and printers. The controller manages messages from these devices and communicates them to the CPU. It also routes output from the CPU to the appropriate peripheral device. Modems Modems are the most common type of communications processor. They convert the digital signals from a computer or transmission terminal at one end of a communications link into analog frequencies that can be transmitted over ordinary telephone lines. A modem at the other end of the communications line converts the transmitted data back into digital form at a receiving terminal. This process is known as modulation and demodulation, and the work modem is a combined abbreviation of those two words. Modems come in several forms, including small stand-alone units, plug-in circuit boards, and removable modem cards for laptop PCs. Most modems also support a variety of telecommunications functions, such as transmission error control, automatic dialing and answering, and a faxing capability. Multiplexer A multiplexer is a device that enables a single communications channel to carry data transmissions from multiple sources simultaneously. The multiplexer divides the communications channel so that it can be shared by multiple transmission devices. The multiplexer may divide a high-speed channel into multiple channels of slower speed or may assign each transmission sources a very small slice of time for using the high-speed channel. Internetwork Processors Telecommunications networks are interconnected by special-purpose communications processors called internetwork processors such as switches, routers, hubs, and gateways. A switch is a communications processor that makes connections between telecommunications circuits in a network so a telecommunications message can reach its intended destination. A router is a more intelligent communications processor that interconnects networks based on different rules or protocols, so a telecommunications message can be routed to its destination. A hub is a port switching communications processor. Advanced versions of hubs provide automatic switching among connections called ports for shared access to a network’s resources. Workstations, servers, printers, and other network resources are connected to ports, as are switching and routers provided by the hub to other networks. Networks that used different communications architectures are interconnected by using a communications process called a gateway. All these devices are essential to providing connectivity and easy access between the multiple LANs and wide area networks that are part of the intranets and client/server networks in many organizations. Telecommunications Software

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Special software for controlling and supporting the activities of a telecommunications network is called telecommunication software. TELECOMMUNICATIONS NETWORK MODEL Generally, a communications network is any arrangement where a sender transmits a message to a receiver over a channel consisting of some type of medium. A simple conceptual model of a telecommunications network consists of five basic categories of components: 1. 2. 3. 4. 5.

Terminals Telecommunications processors Telecommunications channels Computers, and Telecommunications software

Terminals Terminals, such as networked personal computers, network computers, or video terminals. Of course, any input/output device that uses telecommunications networks to transmit or receive data is a terminal, including telephones, office equipment, and the transaction terminals. Telecommunications processors Telecommunications processors, which support data transmission and reception between terminals and computers. These devices, such as modems, switches, and routers, perform a variety of control and support functions in a telecommunications network. For example, they convert data form digital to analog and back, code and decode data, and control the speed, accuracy, and efficiency of the communications flow between computers and terminals in a telecommunications network. Telecommunications Channel Telecommunications channel which data are transmitted and received. Telecommunications channels use combinations of media, such copper wires, coaxial cables, fiber optic cables, microwave systems, and communications satellites, to interconnect the other components of a telecommunications network. Computers Computers of all sizes and types are interconnected by telecommunications networks so that they can carry out their information processing assignments. For example, a mainframe computer may serve as a host computer for a large network, assisted by a midrange computer serving as a front-end processor, while a microcomputer may act as a network server for a small network of microcomputer workstations. Telecommunications Control Software Telecommunications control software consists of programs that control telecommunications activities and manage the functions of telecommunicates networks. Examples include network management programs of all kinds, such as telecommunicates monitors do for mainframe host computers, network operating systems for microcomputer network server, and Web browsers for microcomputers.

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TYPES OF TELECOMMUNICATIONS NETWORKS There are many different types of telecommunication networks. However, from an end user’s point of view, there are only a few basic types, such as wide area and local area networks and interconnected network like internet, intranets, and extranets, as well as client/server and inter-organizational networks. LOCAL-AREA NETWORKS A computer network that covers a fairly small area and uses specially designed hardware in called a local area network or LAN. A local area network uses direct, high speed cables to share hardware, software, and data resources. Typically, a LAN connects the computers in a department, a building, or several buildings situated near each other. Each hardware device on a LAN, such as a computer or printer, is called a node. A LAN integrates anywhere from two or three computers up to several hundred computers. The capability to share resources is a major advantage of a LAN. Because the computers in a LAN share hardware, several people can use the same network printer.

Figure: Local Area Network (LAN) WIDE AREA NETWORKS A network that covers a wide area and uses general purpose communication hardware is called a wide area network, or WAN. A WAN is a computer network that directly connects computers separated by long distances more than a mile and much as half the globe. WANs require special media, which are provided by telephone companies and other firms that specialize in this service. Local area networks may be connected to one another and to wide area networks. Like LANs, WANs enable file exchange, remote database access, electronic mail, teleconferencing and discussion groups. Business has found other uses for WANs. METROPOLITAN AREA NETWORK MANs cover an area of a typical city. They offer a simple and fast way to link different sites of an organization for exchange of information. MANs use technologies similar to LAN technologies. INTERNETWORKS Most local area networks are eventually connected to other LANs in wide area networks. These interconnected networks are generically called internetworks, of which the Internet is the largest example. Such networks enable end users to communicate with the workstations of colleagues on other LANs, or to access the computing resources and databases at other company locations or at other organizations. These interconnected telecommunications networks rely on internetwork processors, such as switches, routers, hubs, or gateways, to make internetworking connections to other LANs and wide area networks.

INTRANETS AND EXTRANETS The goal of many internetwork architectures is to create a seamless network of Internet-like networks called intranets within each organization. This network of intranets is then connected to the Internet and to networks called extranets that provide electronic links to business partners.

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Intranets are designed to be open, but secure, internal networks whose Web browsing software provides easy point-and-click access by end users to multimedia information on internal Web sites. Intranet Web sites may be established on internal Web servers by a company, its business units, departments, and workgroups. For example, a human resources department may establish an intranet Web site so employees can easily access up-to-the-minute information of the status of their benefits accounts, as well as the latest information company benefits options. Extranets are networks that link some of the intranet resources of a company with other organizations and individuals. For example, extranets enable customers, suppliers, subcontractors, consultants, and others to access selected intranet Web sites and other company databases. Organizations can establish private extranets among themselves, or use the Internet as part of the network connections between them. Many organizations use virtual private network (VPNs) to establish secure intranets and extranets. A virtual private network is a secure network that uses the Internet as its main backbone network, but relies on the fire walls and other security features of its Internet and Intranet connections and those of participating organizations. Thus, for example, VPNs would enable a company to use the Internet to establish secure intranets between its distant branch offices and manufacturing plants, and secure extranets between itself and its customers and suppliers.

CLIENT / SERVER NETWORKS Client / server networks have become the predominate information architecture of enterprise wide computing. In a client / server network, end user PC or NC workstations are the clients. They are interconnected by local area networks and share application processing with network servers, which also manage the networks. Local area networks are also interconnected to other LANs and wide area networks of client workstations and servers.

INTERORGANIZATIONAL NETWORKS Many of the application of telecommunications we have just mentioned can be classified as Interorganizational networks. The Internet, extranets, and other networks may be used to link a company’s headquarters and other locations to the networks of its customers, suppliers, and other organizations. For example, you can think of a customer account inquiry system that provides intranet access by employees and extranet access by customers as an example of an Interorganizational network.

PRIVATE BRANCH EXCHANGES A private branch exchange (PBX) is a special-purpose computer designed for handling and switching office telephone calls at a company site. Today’s PBXs can carry both voice and data to create local networks. While the first PBXs performed limited switching functions, they can now store, transfer, hold, and redial telephone calls. PBXs can also be used to switch digital information among computers and office devices. For instance, you can write a letter on a microcomputer in your office, send it to the printer, then dial up the local copying machine and have multiple copies of your letter created. All of this activity is possible with a digital PBX connecting “smart” machines in the advanced office. The advantage of digital PBXs over other local networking options is that they utilize existing telephone lines and do not require special wiring. A phone jack can be found almost anywhere in the office building. Equipment can therefore be moved when necessary with little worry about having to rewrite the building. A hard-wired computer terminal or microcomputer connected to a mainframe with coaxial cable must be rewired at considerable cost each time it is moved. A microcomputer connected to a network by telephone can simply be plugged or unplugged anywhere in the building, utilizing the existing telephone lines. PBXs are also supported by commercial vendors such as the local telephone company, so that the organization does not need special expertise to manage them. The geographic scope of PBXs is limited, usually to several hundred feet, although the PBX can be connected to other PBX networks or to packet-switched networks to encompass a larger geographic area. The primary disadvantage of PBXs is that they are limited to telephone lines and that they cannot easily handle very large volumes of data.

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TELECOMMUNICATIONS SOFTWARE FUNCTIONS Software controls the operations of computer networks. The software that manages the resources of the network is often called the network operating system. A variety of communication software packages are available for microcomputers, especially for Internet Web browsing, like Microsoft Explorer, Netscape Navigator, Microsoft Outlook etc. Several functions are commonly provided by communication software packages, examples are: access control, transmission control, network management, error control, security management etc. ACCESS CONTROL: Access control is responsible for establishing the connection between terminals and computers in a network. Access control activities include connecting links through modems, establishing communication parameters such as speed, mode and direction, automatic telephone dialing and redialing, logging on and off with appropriate account numbers. TRANSMISSION CONTROL: Transmission Control function allows computers and terminals to send and receive commands, messages, data and programs. Data and programs are usually transmitted in the form of files and thus this activity is also called file transfer. ERROR CONTROL: Error control functions involve detection and correction of errors. Communication software and processors detect errors in transmission by different methods, including parity checking and cyclic redundancy checks. Most error correction methods involve retransmission, in which a signal is sent back to the computer to retransmit the previous message which has been received with error. NETWORK MANAGEMENT FUNCTION: Network management function manages communication in a computer network. It also monitors network activity and the use of network resources by end users. Security management is required to protect a computer network from unauthorized access. Network operating systems, or other security programs, restrict access to the data files and other computing resources in networks. Data transmission can also be protected by encryption and authentication techniques. TELECOMMUNICATIONS HARDWARE DEVICES Hardware devices needed at different points in building a network of computer are the following: NETWORK INTERFACE CARD A network interface card (NIC) is a small hardware device that commonly goes inside a computer and enables the connection between the computer and cable. In addition to the physical connection, a NIC also performs different tasks. This includes accessing the common media, transmitting and receiving data bits in forms of electrical signals and so on. MODEM Modem stands for modulator-demodulator. A modem is a device that can connect computers via traditional telephone lines. A modem converts the digital data of computers to analog tones. These tones are transported via the regular telephone lines to the destination computer. Modems come as cards that need to plug inside computers, and as standalone units that need to be connected to the serial port using a serial cable. HUB A hub a networking device used to make star network. A hub hosts different ports to allow connections from computers. A special port may connect to another hub in order to extend number of ports. Inside a passive hub there is little more than electrical wirings. On the other hand, an active hub amplifies the signals from and to different computers. An intelligent or smart hub can detect line faults, segment the network to smaller networks at avoid collisions, and much more. SWITCH A Switch is an intelligent hub. However, switches can also perform functions of bridges. A bridge is used for connecting two LANs. As more the computer, the more collisions in a linear bus LAN, if two or more LANs are needed to be connected, they are connected via bridge or switch. A switch usually isolates the LANs it is connected to, and continuously monitors the traffic. If a data packet is destined for a computer within the same LAN, the switch does nothing. However, if the packet is meant for a computer on another LAN, the switch then forwards the packet on the target LAN. ROUTER A router connects two or more dissimilar networks. Dissimilar networks are not compatible, and any form of data communication among them is not possible without using a router. Routers are expensive, and mainly internet service providers use them. Large business organizations, universities often use routers to directly connect to the Internet.

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TYPES OF TELECOMMUNICATIONS NETWORKS TOPOLOGIES A number of different ways exist to organize telecommunications components to from a network and hence provide multiple ways of classifying networks. Networks can be classified by their shape or topology. Networks can also be classified by their geographic scope and the type of services provided. Wide-area networks, for example, encompass a relatively wide geographic area, from several miles to thousands of miles, whereas local networks link local resources such as computers and terminals in the same department or building of a firm. Topology of a network describes the way the computers and the nodes of the network are interconnected. There are a number of possible topologies:

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The Bus Topology The Ring Topology The Star Topology The Tree Topology The Mesh Topology

More complex networks can be built as hybrids of two or more of the above basic topologies. THE BUS TOPOLOGY Bus networks (not to be confused with the system bus of a computer) use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium, those devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message. However, bus networks work best with a limited number of devices. If more than a few dozen computers are added to a bus, performance problems will likely result. In addition, if the backbone cable fails, the entire network effectively becomes unusable.

Figure: The Bus Network THE RING TOPOLOGY In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (effectively either "clockwise" or "counterclockwise"). A failure in any cable or device breaks the loop and can take down the entire network.

The Ring Network THE STAR TOPOLOGY Many home networks use the star topology. A star network features a central connection point called a "hub" that may be an actual hub or a switch. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet.

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Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable will only take down one computer's network access and not the entire LAN. (If the hub fails, however, the entire network also fails.)

Figure: The Star Network THE TREE TOPOLOGY Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the "root" of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub ports) alone. THE MESH TOPOLOGY Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (Recall that in a ring, although two cable paths exist, messages can only travel in one direction.) Some WANs, like the Internet, employ mesh routing. HOW ORGANIZATIONS USE TELECOMMUNICATIONS FOR COMPETITIVE ADVANTAGE Some of the leading telecommunications applications for communication, coordination, and speeding the flow of transactions, messages, and information throughout business firms are electronic mail, voice mail, facsimile machines (FAX), digital information services, teleconferencing, data conferencing, videoconferencing, and electronic data interchange. ELECTRONIC MAIL (E-MAIL): The computer to computer exchange of message. A person can use a Microcomputer attached to a Modem or a Terminal to send notes and even lengthier documents just by typing the mail address of the message’s recipient. VOICE MAIL: This is a system that “Digitizes a Spoken Message” of the sender & transmitting it over a Network and stores the messages on Disk for later retrieval. When the recipient is ready to listen, the messages are ‘Converted” to audio form FAX / FACSIMILE: Fax is a machine that “Digitizes and Transmits Documents with both Text and Graphics” over telephone line. A sending FAX machine Scans and Digitizes the document image. The Digitized document is then transmitted over a Network and Reproduced in hard copy form by a receiving FAX machine. TELECONFERENCING: Teleconferencing allows a group of people to communicate simultaneously via Telephone or “Group Communication Software”. DATA CONFERENCING: Teleconferencing that allows two or more people at distance locations to work on the same Document or Data simultaneous is called Data conferencing. Here all participants can edit, modify the same data or document. VIDEOCONFERENCING: Teleconferencing that has capability to let participants see each other “Face-to-Face” over Video Screens is Videoconferencing. Videoconferencing is little more expensive than others. ELECTRONIC DATA INTERCHANGE (EDI): EDI is the direct Computer to Computer exchange between two organizations of standard business transaction documents like; Invoice, Work Order, Purchase Order etc. EDI Saves MONEY and TIME because transactions can be transmitted from one system to another through Telecommunication Network: Eliminating Printing and Mailing costs. EDI can give competitive advantage over competitors by selling product over the Network. ELECTRONIC FUND TRANSFER (EFT): Through EFT people can pay for goods and services by having funds transferred from various accounts electronically. Through ATM machine you can transfer

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your funds from one account to another. You also can transfer your Electric, Telephone, Water etc bills through your credit card.

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FACTORS BEFORE CHOOSING A NETWORK Once an organization has developed a business telecommunications plan, it must determine the initial scope of the telecommunications project. Deciding which telecommunications technology to adopt, and under what circumstances, can prove difficult, given the rapid rate of change in the technology and in the related costs of telecommunications. Managers should take eight factors into account when choosing a telecommunications networks. DISTANCE: If the communication will be entirely internal of the organization’s buildings in that case LAN can meet the purpose to the Network. RANGE OF SERVICE: A network must have services like e-mail, Electronic Data Interchange, Voice Mail, Videoconferencing etc capabilities. SECURITY: Maximum security facility is essential for any network in the organization. Since any one can “Tap” the ordinary line, it is recommended to get dedicated leased line. MULTIPLE ACCESSES: Sometimes two or more Nodes are required to log into Network, in that case you may consider a “Proxy Server”. UTILIZATION: One must consider the load he is going to put to the Network. If load is too much the Network can be pretty slow. COST: Cost is an important issue to think before choosing a Network; expense are involved both before and after the installation is done; Development, Operations, Expansion and Maintenance. INSTALLATION: Make sure the building is properly constructed to install fiber optics. Because if the building does not has proper wiring channels underneath the floors, installing Fiber Optic Cable is going to be extremely difficult. CONNECTIVITY: Different companies has different standards for Hardware, Software and Communication Devices, that can be sometime very difficult to get all the components of a Network to “Talk” to each other. So it is important to make sure that all the devices you are installing are going to communicate with each other.

REVIEW QUESTIONS

1.

What is a telecommunications system? What are the principal functions of all telecommunications systems?

2.

Describe Telecommunications Network Model.

3.

Describe the types of telecommunication networks.

4.

Distinguish between a PBX and a LAN.

5.

Name and briefly describe each of the components of a telecommunications system.

6.

Distinguish between an analog and a digital signal.

7.

Name and describe the different types of telecommunications transmission media.

8.

What is the relationship between bandwidth and the transmission capacity of a channel?

9.

What is the difference between synchronous and asynchronous transmission?

10. What is the difference between half-duplex, duplex and simplex transmission? 11. Explain the major functions of network software. 12. With the help of illustrations briefly explain the network topologies.

13. Name and briefly describe the different kinds of telecommunications processors. 14. Name and briefly describe the network topologies. 15. Name and describe the telecommunications applications that can provide strategic benefits to businesses. 16. What are the principal factors to consider when developing a telecommunications plan?

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