Telecommunications

The purpose of this chapter is to provide an introduction to important concepts needed by business end users.

Section I: A Manager's View of Telecommunications

1. Discusses basic trends and functions of telecommunications networks

Section II: Technical Telecommunications Alternatives

1. Reviews some of the major technical characteristics of telecommunications networks for a basic understanding of this technology by managerial end users.

Learning Objectives

Identify the basic components, functions, and types of telecommunications networks.

Identify several major developments and trends in the industries, technology, and applications of telecommunications.

Explain the functions of major types of telecommunications network hardware, software, and media.

Section I: A Manager’s View of Telecommunications

End users need to communicate electronically to succeed in today's global information society. Managers, end users, and their organizations need to electronically exchange data and information with other end users, customers, suppliers, and other organizations. Only through the use of telecommunications can they perform their work activities, manage organizational resources, and compete successfully in today's fast changing global economy. Many organizations today could not survive without interconnected networks of computers to service the information processing and communications needs of their end users.

Telecommunications The sending of information in any form from one place to another using electronic or light-emitting media.

Data Communications Describes the transmitting and receiving of data over communication links between one or more computer systems and a variety of input/output terminals.

Teleprocessing The integration of telecommunications and computer-based

Telematics, & Telephony information processing technologies.

Telecommunications networks provide invaluable capabilities to organizations and its end users.

For example:

1. Enable end users to communicate electronically and share hardware, software, and data resources [LAN]

2. Enable a company to process transactions immediately from many remote locations, exchange business documents electronically with customers and suppliers, or remotely monitor and control production processes [WAN].

3. Interconnect the computer systems of a business so their computing power can be shared by end users throughout an enterprise.

4. Enhance collaboration and communication among individuals both inside and outside an organization.

Telecommunications applications are grouped into three major categories:

1. Electronic communications systems

2. Electronic meeting systems

3. Business process systems.

Trends in Telecommunication

Major trends occurring in the field of telecommunications have a significant impact on management decisions in this area. Informed managerial end users should thus be aware of major trends in telecommunications industries, technologies, and applications that significantly increase the decision alternatives confronting their organizations.

Telecommunications Industry Trends:

The number of vendors and carriers offering telecommunications services has increased. As well, the service and vendor options available to meet a company's telecommunications needs have increased significantly, as has a manager's decision-making alternatives.

Telecommunications Technology Trends:

The telecommunications technology trend is changing from analog to digital network technologies. Technology is rapidly converting to digital transmission networks, which transmit information in the form of discrete pulses, rather than waves.

Digital transmission offers:

1. Higher transmission speeds (transmits with pulses)

2. Movement of larger amounts of information

3. Greater economy

4. Much lower error rates than analog systems

5. Integrated Services Digital Network (ISDN) technology allows networks to carry multiple types of communications (data, voice, and video) on the same circuits.

Another major trend in telecommunications technology is a change in communications media. Many telecommunications networks are changing from copper wire-based media and land-based microwave relay systems to fiber optic lines and communications satellite transmissions.

Fiber optic transmission, which uses pulses of a laser-generated light offer significant advantages in terms of:

l. Reduced size and installation effort

2. Greater communication capacity

3. Freedom from electrical interference

For organizations that need to transmit massive quantities of data over global networks, satellite transmission offers significant advantages in:

1. Speed

2. Capacity

Another major telecommunications trend is toward easier access by end users to the computing resources of inter-connnected networks. This trend is based on both industry and technical moves toward building networks based on an open systems architecture.

Some of the distinguishing features of open systems are:

1. They use common standards for hardware, software, applications, and networking.

2. They create a computing environment that is open to easy access by end users and their networked computer systems.

3. They provide greater connectivity (ability of networked computers and other devices to easily access and communicate with each other and share information).

4. They provide a high degree of network interoperability (enable the many different applications of end users to be accomplished using the different varieties of computer systems, software packages, and databases provided by a variety of interconnected networks).

 

There is a significant change in the business use of telecommunications. The trend toward more vendors, services, advanced technologies, and open systems dramatically increases the number of feasible applications. Telecommunications is playing a more important role in support of the operations, management, and strategic objectives of both large and small companies. Telecommunications is becoming an integral part of computer-based information systems.

It is used to:

1. Cut Costs

2. Improve the collaboration of work groups

3. Develop on-line operational processes

4. Share resources Lock in customers and suppliers

5. Develop new products and services.

Thus, the trend is toward the pervasive use of telecommunications networks in support of business operations, managerial decision making, and strategic advantage in domestic and global markets.

The Information Superhighway:

The trend toward open, high-speed, digital networks with fiber optic and satellite links has made the concept of an information superhighway technically possible, and has captured the interest of both business and government.

The information superhighway can have dramatic impacts on a business organization. As well, it promises to have a major impact on developments in telecommunications and on our national economic and social life.

A Telecommunications Network Model:

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 telecommunications network consists of five basic categories of components:

I/O devices that use telecommunications networks to transmit or receive data. They include:

l. Video Terminals

2. Microcomputers

3. Telephones

4. Office Equipment

5. Transaction Terminals

Support data transmission and reception between terminals and computers. They include:

l. Modems

2. Multiplexers

3. Front-end Processors

Telecommunications Channels and Media

Telecommunications channels are the part of a telecommunications network that connects the message source with the message receiver. They include the physical equipment used to connect one location to another for the purpose of transmitting and receiving information.

Data are transmitted and received over channels, which use a variety of telecommunications media. Media include:

l. Copper Wires

2. Coaxial Cables

3. Fiber Optic Cables

4. Microwaves Systems

5. Communications Satellites

Computers

Computers of all sizes and types are interconnected by telecommunications networks. They include:

l. Host Computers (mainframes)

2. Front-End Processors (minicomputers)

3. Network Servers (microcomputers)

Telecommunications Control Software

Consists of programs that control telecommunications activities and manage the functions of telecommunications networks. They include:

1. Telecommunications Monitors (mainframe host computers)

2. Network Operating Systems (microcomputer network servers)

3. Communications Packages (microcomputers)

There are many different types of telecommunications networks. However, from an end user point of view, there are two basic types: wide area and local area networks. What should be clearly pointed out to students is that there is a growing trend toward the increased use of LAN's and WAN's as an alternative to the use of terminals connected to minicomputers or smaller mainframes for end user computing in many organizations.

Telecommunications networks that cover large geographic areas are known as wide area networks. These networks cover areas such as:

l. Large city or metropolitan area

2. Whole country

3. Many countries and continents

Telecommunications networks that connect information processing devices within a limited physical area. These networks cover areas such as:

l. Offices

2. Buildings

3. Manufacturing plant

Some of the characteristics of LAN include the following:

1. LAN's use a variety of telecommunications media, such as ordinary telephone wiring, coaxial cable, or wireless radio systems to interconnect microcomputer workstations and computer peripherals.

2. LAN's use a powerful microcomputer with a large disk capacity as a file server or network server that contains a network operating system program (e.g., Novell) that controls telecommunications and the use of network resources.

3. LANs may be connected to WANs by communications processors forming a common interface called a gateway.

4. LANs allow end users in a work group to communicate electronically; share hardware, software, and data resources; and pool their efforts when working on group projects.

Most local area networks are eventually connected to other LANs or WANs to create inter-networks. Inter-networks enable end users to communicate with the workstations of colleagues on other LAN, or to access the computing resources and databases at other company locations or at other organizations. This frequently takes the form of client/server networks, where end user microcomputer workstations (clients) are connected to LAN servers and interconnected to other LANs and their servers, or to WANs and their mainframe super-servers.

In order to make internetworking connections possible, LANs rely on inter-network processors

such as:

1. Bridges

2. Routers

3. Hubs

4. Gateways

Client Server computing is a grown trend in most organizations. Computing power has rapidly become distributed and interconnected throughout many organizations through networks of all types of computers. Characteristics of a client/server network are:

1. End user microcomputer workstations are the clients.

2. Clients are interconnected by local area networks and share application processing with LAN servers, which also manage the networks.

3. LANs may be interconnected to other LANs and wide area networks of client workstations and servers.

Benefits of client server computing include:

1. Clients (end users) can perform some or most of the processing of their business applications.

2. LAN servers can share application processing, manage work group collaboration, and control common hardware, software, and databases.

3. Data can be completely processed locally, where most input and output must be handled.

4. Provides access to the workstations and servers in other networks.

5. Computing processing is more tailored to the needs of the end users.

6. Increases information processing efficiency and effectiveness as users are more responsible for their own application systems.

7. Allows large central-site computers to handle the jobs they do best - such as high-volume transaction processing, communications network security and control, and maintenance and control of large corporate databases.

8. Clients at local sites can access the corporate superservers to receive corporate wide management information or transmit summary transaction data reflecting local site activities.

Client/server computing is the latest form of distributed processing.

Information processing activities in an organization are accomplished by a network of computers interconnected by telecommunications links instead of relying on one large centralized computer facility or on the decentralized operation of several independent computers.

Cooperative Processing

Allows the various types of computers in a distributed processing network to share the processing parts of an end user's application. Application software packages are available which have common user interfaces and functions so they can operate consistently on networks of micro, mini, and mainframe computer systems. Client/server computing may also involve cooperative processing.

Interorganizational Networks:

Many applications of telecommunications can be classified as inter-organizational networks. Businesses are using telecommunications to:

1. Link a company's wide area and local area networks to the networks of customers and suppliers both domestically and internationally.

2. Build new strategic business relationships and alliances with their stakeholders in an attempt to increase and lock in their business, while locking out competitors.

3. Reduce transaction processing costs. Increase the quality of service.

4. Connection to information service providers, and other external organizations provides better information for management decision making.

 

The Internet is the largest "network of networks" today, and the closest model we have to the information superhighway of tomorrow.

Distinguishing features of the Internet include:

1. The Net does not have a central computer system or telecommunications center. Instead each message sent on the Internet has an address code so any computer in the network can forward it to its destination.

2. The Net does not have a headquarters or governing body.

3. User of the Net is growing rapidly.

4. The most popular Internet application is E-Mail. Other applications include assessing files and databases from libraries and organizations, and holding real-time conversations with other Internet users.

5. The Net supports bulletin board systems.

Businesses using the Internet is expanded rapidly. Business is conducted on the Internet for several reasons:

1. Ease of worldwide communications with colleagues, consultants, customers and suppliers.

2. Links workstations together to form virtual work groups to work on joint projects such as product development, marketing campaigns, and scientific research.

3. Allows for collaboration through Internet' s global E-Mail and bulletin board systems (BBS).

4. Access to a vast range of information provided by the networks on the Internet.

5. Internet represents the wave of the future in business telecommunications.

Special software programs are required to access the Internet. Examples include:

1. Gopher

2. Mosaic

3. Netscape

Section II: Technical Telecommunications Alternatives

Technical Telecommunications Alternatives:

Telecommunications is a highly technical, rapidly changing field of information systems technology. Most end users do not need a detailed knowledge of its technical characteristics. However, they need a basic understanding and appreciation for some of the important characteristics of the basic components of telecommunications networks.

To get from here too there, data must move through something. A telephone line, a cable, or the atmospheres are all forms of transmission media, or channels. Telecommunications channels (communication lines or links) are the means by which data and other forms of communications are transmitted between the sending and receiving devices in a telecommunications network.

Telecommunications media are the physical media used by telecommunications channels. They include:

1. Twisted-Pair Wire

2. Coaxial Cables

3. Fiber Optic Cables

4. Terrestrial Microwave

5. Communications Satellite

6. Cellular

7. Wireless LAN

Ordinary telephone wire, consisting of copper wire twisted into pairs (twisted pair wire).

1. Most widely used media for telecommunications

2. Used in established communications throughout the world

3. Used for both voice and data transmissions

4. Used extensively in home and office telephone systems and many LANs and WANs.

Disadvantages:

1. Susceptible to a variety of types of electrical interference (noise), which limits the practical distance that data can be transmitted without being garbled.

2. Signals must be "refreshed" every one to two miles through the use of repeaters which are very expensive.

3. Does not offer security.

Copper or aluminum wire wrapped with spacers to insulate and protect it. Insulation minimizes interference and distortion of the signals the cable carries.

1. Can carry a large volume of data -about 100 million bits per second (1800 to 3600 voice calls at once). A 1/2" diameter coaxial cable can carry up to 5,500 channels

2. Coaxial cables can be bundled together into a much larger cable for ease of installation.

3. Can be placed underground & laid on the floors of lakes and oceans.

4. Allow for high-speed data transmission are used in high-service metropolitan areas for cable TV systems, and for short-distance connection of computers and peripheral devices.

5. Used extensively in office buildings and other work sites for local area networks.

Disadvantages:

1. More expensive than twisted pair

Cables consisting of one or more hair-thin filaments of glass fiber wrapped in a protective jacket.

Signals are converted to light form and fired by laser in bursts.

1. Relatively low cost

2. Offer high transmission volume. A 1/2" diameter fiber optic cable can carry up to 50,000 channels.

3. Can carry digital signals, as well as analog thus increase communications and capability.

4. Provide substantial size and weight reductions

5. Provide increased speed and greater carrying capacity than coaxial cable and twisted-pair lines. Are not affected by and do not generate electromagnetic radiation.

6. Are not susceptible to electronic noise and so have much lower error rates than twisted pair and coaxial cable.

7. Speed of communications is 10,000 times faster than that of microwave and satellite systems.

8. Message security as fiber optics communications is very resistant to illegal data theft, taps can be easily detected.

9. Can be used undersea for transatlantic use

Biggest disadvantages of using fiber optic are:

1. Installation can be difficult as splicing the cable to make connections is not easy, however, it this disadvantage also offers an advantage as the lines are more secure in that it makes tapping them difficult.

2. Costly to purchase

3. Specialized communications equipment is expensive.

Involves earthbound microwave systems which transmit high-speed radio signals in a line-of-sight path between relay stations spaced approximately 30 miles apart.

1. Use the atmosphere as the medium through which to transmit signals.

2. Used extensively for high-volume as well as long-distance communication of both data and voice in the form of electromagnetic waves

Disadvantages:

1. Microwave signals cannot bend around the curvature of the earth; instead they must be relayed from point to point by microwave towers, or relay stations, placed approximately 30 miles apart. (The surface of the earth typically curves about 8 inches every mile).

2. Saturation of the airwaves with microwave transmissions has reached its maximum.

Communication satellites use the atmosphere as the medium through which to transmit signals. A satellite is some solar-powered electronic devices that receives, amplify, and retransmit signals; the satellite acts as a relay station between satellite transmissions stations on the ground (earth stations). Three satellites placed in orbit can cover the entire surface of the earth, with some overlap.

1. Used extensively for high-volume as well as long-distance communication of both data and voice.

2. Cost-effective method for moving large quantities of data over long distances.

Disadvantages:

1. Satellites are very expensive to develop and place in orbit.

2. Signals weaken over long distances, weather conditions and solar activity can cause noise interference.

3. A satellite is useful for only 7-10 years.

4. Anyone can listen in on satellite signals, so sensitive data must be sent in a secret, or encrypted form.

5. Depending on the satellite's transmission frequency, microwave stations on earth can "jam," or prevent, transmission by operating at the same frequency.

6. Signal transmission may be slow if the signals must travel over very long distances.

Is a radio communications technology that divides a metropolitan area into honeycomb cells. This technology is used to support mobile phone service, and mobile voice and data communications.

1. Important communications medium for mobile voice and data communications.

Disadvantage:

1. Not secured lines

Are used to connect LANs without the additional cost or inconvenience of wiring a building.

1. LAN radio uses radio transmissions to interconnect LAN components.

2. Infrared uses beans of infrared light to establish network links between LAN components.

3. Wireless LAN technology makes LANs easy to set up, relocate, and maintain.

Disadvantages:

1. High initial costs

2. Distance limitations.

Telecommunications channels for wide area networks can be owned by an organization or provided by other companies.

Common carriers provide the wide area communications networks used by most computer-using firms and individuals. They specialize in providing a selected number of communication services to the public.

Value added carriers lease communication lines from common carriers and offer communication services to customers. Networks of such carriers are known as value-added networks (VAN's), because they add "value" to their leased lines by using communications hardware and software their expertise to provide various data communications services.

Telecommunications Processors:

Are hardware devices that perform a variety of support functions between the terminals and computers in a telecommunications network. A telecommunications processor includes:

1. Modems

2. Multiplexers

3. Bridges

4. Front-End Processors

Modems:

Modems are the most common type of communications processor, and is probably the most widely used data communications hardware in business. Functions of modems include the conversion of digital computer signals to analog signals for transmitted over telephone lines, then to receive these signals and convert them back to digital signals. This process is known as modulation and demodulation. The word "modem" is a contraction of modulate and demodulate.

Multiplexers

A multiplexer is a communications processor that allows a single communications channel to carry simultaneous data transmissions from many terminals. Typically, a multiplexes merges the transmnissions of several terminals at one end of a communications channel, while a similar unit separates the individual transmissions at the receiving end.

Many LANs are interconnected by inter-network processors such as bridges, routers, hubs, or gateways to other LANs or wide area networks.

Connects two similar LANs (LANs based on the same network standards or protocols).

Router

Is a communications processor that connects LANs to networks based on different protocols.

Hub

Is a post switching communications processor. This allows for the sharing of the network resources such as servers, LAN workstations, printers etc.

Gateway

Is a communications processor that connects networks that use different communications architectures.

The private branch exchange (PBX) is a communications processor that serves as a switching device between the telephone lines within a work area and local telephone company's main telephone lines (trunks). Functions of a PBX include:

1. Route telephone calls

2. Automatic forwarding

3. Conference calling

4. Least-cost routing of long-distance calls

5. Some PBX's can control communications among terminals, computers, and other information processing devices in office LANs.

 

In some computer systems, the main computer is connected directly into the multi-plexer, controller, or concentrator. In other systems, it is first hooked to a front-end processor. A front end processor is typically a minicomputer. Functions of front end processors include:

1. Handling the data communications control functions for large mainframe host computers.

2. Act as "mediator" between the network and the main computer, allowing the main computer to concentrate on processing and improving the responsiveness of the system to the user.

3. Utilize telecommunications control programs to:

a. Provide temporary buffer storage

b. Data coding and decoding

c. Error detection and recovery

d. Recording, interpreting, and processing of control information

e. Poll remote terminals to determine if they have a message to send or if they are ready to receive a message

f Controls access to a network and allows only authorized users to use the system

g. Assigns priorities to messages

h. Logs all data communications activity

i. Computes statistics on network activity

j. Routes and reroutes messages among alternative communications links.

Software is a vital component of all telecommunications networks. Communications control software includes programs stored in the host computer as well as programs in front-end computers and other communications processors. Such software controls and supports the communications occurring in a telecommunications network. Telecommunications software packages for mainframe-based WANs are frequently called telecommunications monitors or teleprocessing monitors. LAN's rely on software called network operating systems, e.g., Novell NetWare or Microsoft LAN manager. Functions of telecommunications software include:

Telecommunications software packages provide a variety of communications support services. Several major functions commonly provided by telecommunications software include:

1. Access Control

2. Transmission Control

3. Network Management

4. Error Control

5. Security Management

This function establishes the connections between terminals and computers in a network. It may involve.

1. Connects and disconnects communications links and establish communications parameters such as transmission speed, mode, and direction.

2. Automatic telephone dialing and redialing

3. Logging on and off with appropriate account numbers and security codes

4. Automatic answering of telephone calls from another computer.

This function allows computers and terminals to:

1. Send and receive commands, messages, data, and programs (file transfer).

2. Error checking and correction of data transmissions may also be provided.

This function manages communications in a telecommunications network. It may involve:

1. Determine transmission priorities, routes messages, polls, and terminals in the network, and forms waiting lines (queues) of transmission requests.

2. Logs statistics of network activity and the use of network resources by end user workstations.

This function involves detection and correction of transmission errors. Errors are usually caused by distortions in the communications channel, such as line noise and power surges. Control errors in transmission by several methods:

1. Parity checking

2. Control code checking

3. Retransmissions of the message.

This function protects a communications network from unauthorized access by restricting access to data files and other computing resources in LANs and other types of networks. Restriction usually involves:

1. Control procedures that limit access to all or parts of a network by various categories of users, as determined by the network manager or administrator of the network.

2. Automatic disconnection and callback procedure may be used.

3. Data transmissions can be protected by coding techniques called encryption.

Telecommunications Network Topologies:

Data communications lines can be connected in two types of configurations (topologies):

1. Point-to-point lines

2. Multidrop lines

1. Each terminal (sending and receiving) is directly connect by their own line.

2. Point-to-point lines are more expensive than multi-drop lines.

3. Point-to-point lines are used if there will be continuous connections between a computer and a terminal or other computer system.

Multidrop Line:

1. Connects many devices, not just one sending device and one receiving device.

2. Cheaper than point-to-point lines because each line is shared by many terminals.

3. Communications processors such as multi-plexers and concentrators are used on multi-drop lines to help many terminals share the same line.

 

Star, Ring, and Bus Networks Topologies:

These are three basic topologies used in WAN’s and LAN’s telecommunications networks.

The star network a popular network configuration, involves a central unit that has a number of terminals tied into it.

1. Ties end user computers to a central computer.

2. The central unit in the star network acts as the traffic controller among all the other computers tied to it. The central computer is usually a mainframe (host) which acts as the file server.

3. Star network is well suited to companies with one large data processing facility shared by a number of smaller departments. Many star networks take the form of hierarchical networks with a centralized approach.

For example:

Large Headquarters Computers (Headquarters Level) -> connected to:

Medium-Sized Computers (Divisional Level) -> connected to:

Small Computers (Departmental Level or Work Group Level).

Advantages of the star network:

1. Several users can use the central unit at the same time.

Disadvantages of the star network:

1. Disadvantage is that the whole network is affected if the main unit "goes down," and all communications stops.

2. Considered less reliable than a ring network since the other computers in the star are heavily dependent on the central host computer. If it fails, there is no backup processing and communications capability, and the local computers will be cut off from the corporate headquarters and from each other. Fault Tolerance becomes very important.

3. Cost of cabling the central system and the points of the star together are very high.

A ring network is much like a bus network, except the length of wire, cable, or optical fiber connects to form a loop

1. Local computer processors are tied together sequentially in a ring; with each device being connected to two other devices.

2. Ring network has a decentralized approach.

3. Ring network is often used to link mainframes over wide distances.

4. Considered more reliable than less costly than star networks because if one computer the other computers in the ring can continue to process their own work and communicate with each other.

Advantages:

1. Ring networks do not require a central computer to control activity nor does it need a file server.

2. Each computer connected to the network can communicate directly with the other computers in the network by using the common communications channels, and each computer does its own independent applications processing.

3. When one computer needs data from another computer, the data is passed along the ring. The ring network is not as susceptible to breakdowns as the star network, because when one computer in the ring fails, it does not necessarily affect the processing or communi- cations capabilities of the other computers in the ring.

In a bus network, a number of computers are connected by a single length of wire, cable, or optical fiber.

1. All communications travel along this cable, which is called a bus.

2. Bus networks have a decentralized approach

Advantages:

1. There is no host computer or file server.

2. Often used to hook up a small group of microcomputers that share data.

3. Not as expensive as the star network, and, if one of the microcomputers fails, it does not affect the entire network.

In most cases, distributed processing systems use a combination of star, ring, and bus approaches.

Until recently, there was a lack of sufficient standards for the interfaces between the hardware, software, and communications channels of data communications networks. For this reason there is often a lack of compatibility between the data communications hardware and software of different manufacturers. This situation has:

1. Hampered the use of data communications

2. Increased data communications costs

3. Reduced data communications efficiency and effectiveness.

The goal of network architectures is to promote an open, simple, flexible, and efficient telecommunications environment. This is accomplished by the use of:

1. Standard protocols

2. Standard communications

3. Hardware and software interfaces

4 Design of a standard multilevel interface between end users and computer systems.

Protocols

Protocol is the formal set of rules for communicating, including rules for timing of message exchanges, the type of electrical connection used by the communications devices, error detection techniques, means of gaining access to communications channels, and so on. The goal of communications network architectures is to create more standardization and compatibility among communications protocols.

Some groups are working on the establishment of a standard protocol for data transmission. Examples include:

1. SNA IBMs Systems Network Architecture

2. DNA Digital Network Architecture

3. OSI International Standards Organization (ISO)

The Integrated Services Digital Network (ISDN) is a set of standards establish for public and private digital telecommunications networks. It is designed to set rules for a worldwide digital communications network that could simultaneously support voice, data, and image and video transmissions over telephone lines throughout the world.

The form or method of communications affects the maximum rate at which data can be moved through the channel and the level of noise that will exist. The communications capabilities of telecommunications channels can be classified by band width.

Is the frequency ranges of the channel, which determines the channel's maximum transmission rate.

The number of times per second that a data communications signal changes; with each change, one or more bits can be transmitted - bits per second (BPS).

Voiceband

Are low-speed analog channels which are normally used for voice communications, but can also be used for data communications by microcomputers, video terminals, and fax machines.

Are specially conditioned leased lines that can handle faster transmission.

Are high-speed digital channels which allow transmission rates at specific intervals. They typically use microwave, fiber optics, or satellite transmission.

When signals are transmitted through modems from one computer to another, patterns of bits coded to represent data are sent one bit at a time at irregular intervals, as the user inputs data. How does the receiving device know where one character ends and another start?

There are two modes of transmitting data:

1. Asynchronous

2. Synchronous

Asynchronous

Transmits one character at a time, with each character preceded by a start bit and followed by a stop bit, and an error check bit (parity bit). Are used for low-speed transmission rates (below 2400 BPS).

Synchronous

Transmits groups of characters at a time, with the beginning and end of a character determined by the timing circuitry of a communications processor. Are used by large computers to transmit huge volumes of data at high speed (above 2400). Synchronous transmissions require expensive and complex timing devices in order to keep the transmission activities synchronized.

To transmit data in a network, there are various switching alternatives:

A link is established between the sender and the receiver, which remains in effect until the communications session is completed (e.g., telephone).

A message is transmitted a block at a time from one switching device to another.

Involves subdividing communications messages into packets, typically 128 characters long, which are reassembled into the messages at the receiver end.

Access Methods

Common telecommunications access methods are needed to control the access of communication channels in networks in order to avoid conflict, since channels shared by multiple users or devices.

A host computer or communications processor contacts (polls) each device in sequence to determine which one has messages to send.

Line use is on a first come, first served basis, where a device can transmit data if the channel is not in use, but must wait if it is busy.

A special signal code, or token, is sent around the network, and if a device wants to transmit a message, it must wait for the token to come by, examine it to see if it is not in use, and attach its message to the token with destination information.

Key Terms and Concepts

Applications of Telecommunications

Telecommunications applications are being used to service the communications and information processing needs of companies and their end users. Telecommunications technology is allowing for the integrating of voice, data, and video in order to build global networks.

Business Use of the Internet

The Internet is being used to form an information superhighway to support business operations, managerial decision making, and strategic advantage in a global economy.

A radio communications technology that divides a metropolitan area into a honeycomb of cells to greatly increase the number of frequencies and thus the users that can take advantage of mobile phone service.

Client/Server Computing

A computing environment where end user workstations (clients) are connected to micro or mini LAN (servers) possible to mainframe (superserver).

Coaxial Cable

A sturdy copper or aluminum wire wrapped with spacers to insulate and protect it. Groups of coaxial cables may be bundled together in a bigger cable for ease of installation.

Common Carriers

An organization that supplies communications services to other organizations and to the public as authorized by government agencies.

Communications Satellites

Earth satellites placed in stationary orbits above the equator that serve as relay stations for communications signals transmitted from earth stations.

Cooperative Processing

Information processing which allows the computers in a distributed processing network to share the processing of parts of an end user's application.

Distributed Processing

A form of decentralization of information processing made possible by a network of computers dispensed throughout an organization. Processing of user applications is accomplished by several computers interconnected by a telecommunications network rather than relying on one large centralized computer facility or on the decentralized operation of several independent computers.

Fiber Optic Cables

The technology that uses cables consisting of very thin filaments of glass fibers that can conduct the light generated by laser at frequencies that approach the speed of light.

Front-End Processors

Typically a smaller, general-purpose computer that is dedicated to handling data communications control functions in a communications network thus relieving the host computer of these functions.

Host Computer

Typically a larger central computer that performs the major data processing tasks in a computer network.

A proposed national network of interconnected local, regional, and global networks that would support interactive voice, data, video, and multimedia communications.

A global network of millions of business, government, educational, and research networks, computer systems, and end users.

Inter-networks enable end users to communicate with the workstations of colleagues on other LAN, or to access the computing resources and databases at other company locations or at other organizations

Inter-Network Processors

Many LANs are interconnected by inter-network processors such as bridges, routers, hubs, or gateways to other LANs or wide area networks.

Telecommunications networks that inter-connect organizations with other organizations, such as businesses and their customers and suppliers.

A communications network that typically connects computers, terminals, and other computerized devices within a limited physical area such as an office, building, manufacturing plant, or other work site.

A device that converts the digital signals from input/output devices into appropriate frequencies at a transmission terminal and converts them back into digital signals at a receiving terminal.

Multi-Plexers

An electronic device that allows a single communications channel to carry simultaneous data transmission from many terminals.

The software that manages a local area network (e.g., Novell). This software controls telecommunications and the use of network resources.

Network Server

LAN's use a powerful microcomputer with a large disk capacity as a file server or network server. The server handles resource sharing and telecommunications.

Model of network protocols enabling any computer connected to a network to communicate with any other computer on the same network or a different network, regardless of the manufacturer.

Private Branch Exchange

A switching device that serves as an interface between the many telephone lines within a work area and the local telephone company's main telephone lines or trunks. Computerized PBXs can handle the switching of both voice and data in the local area networks that are needed in such locations.

A set of rules and procedures for the control of communications in a communications network.

Telecommunications channels are the part of a telecommunications network that connects the message source with the message receiver. It includes the physical equipment used to connect one location to another for the purpose of transmitting and receiving information.

Telecommunications media are the physical media used by telecommunications channels. They include, twisted-pair wire, coaxial cables, fiber optic cables, terrestrial microwave, communications satellite, cellular, and infrared systems.

A computer program that controls and supports the communications between the computers and terminals in a telecommunications network.

Is any arrangement where a sender transmits a message to a receiver over a channel consisting of some type of medium.

A master plan for building an integrated telecommunications capability to support business objectives.

Telecommunications components include terminals, telecommunications processors, telecommunications channels and media, computers, and telecommunications control software.

Telecommunications Topology

Data communications lines can be connected in two types of configurations (topologies) - point-to-point lines and multi-drop lines.

Telecommunications Processors

Multi-plexers, concentrators, communications controllers, and cluster controllers that allow a communications channel to carry simultaneous data transmissions from many terminals. They may also perform error monitoring, diagnostics and correction, modulation-demodulation, data compression, data coding and decoding, message switching port.

Trends in Telecommunications

Toward a greater number of competitive vendors, carriers, and services; toward integrated, digital, global networks for voice, data, and video, with heavy use of fiber optic lines and satellite channels; toward the pervasive use of telecommunications networks in support of business operations, managerial decision making, and strategic advantage in global markets.

Value-Added Carriers

Third-party vendors who lease telecommunications lines from common carriers and offer a variety of telecommunications service to customers.

Wide Area Networks (WAN)

A data communications network covering a large geographical area.

Wireless LANs