Describe the main components of a network including hardware and software.
Main components of a network including hardware and software.
Telecommunications is the sending of information in any form (e.g voice, data, text, and images) from one place to another using electronic or light-emitting media. Data communications is a more specific term that describes the transmitting and receiving of data over communication links between one or more computer systems and a variety of input/ output terminals. The terms teleprocessing and Telamatics may also be used since they reflect the integration of telecommunications and computer-based information processing technologies.
A Telecommunications Networks Mode.
Generally, a communications network is any arrangement where a sender transmits a message to a receives over a channel consisting of some type of medium.
Terminals: such as video display terminals and other end user workstations. Of course any input/output device that uses tele-communications networks to transmit or receive data is a terminal, including microcomputers, telephones, office equipment, and the transaction terminals.
Telecommunications processors: which support data transmission and reception between terminals and computers. These devices, such as modems, multiplexers, and front-end processors, perform a variety of control and support functions in a telecommunications network. For example, they covert data from digital to analog and back, code and decode data and control the accuracy and efficiency of the communications flow between computers and terminals in a telecommunications network.
Telecommunications channels and media: over which data are transmitted and received. Telecommunications channels use combinations of media, such as copper wires, coaxial cables, fiber optic cables, microwave systems, and communications satellite systems, to interconnect the other components of a telecommunications network.
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 assisted by minicomputers serving as “front-end” computers in managing the activities of end user microcomputers in a telecommunications network.
Telecommunications control software: consists of programs that reside in host computer systems, communications control computers, and end user computers. They control telecommunications input/output activities and manage the functions of telecommunications networks.
Telecommunications channels (also called communications 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. A telecommunications channel makes use of a variety of telecommunications media. These include twisted-pair wire, coaxial cables, and fiber optic cables, all of which physically link the devices in a network. Also included are microwave systems, communications satellite systems, and cellular radio, all of which use microwave and other radio waves to transmit and receive data.
Ordinary telephone wire, consisting of copper wire twisted into pairs (twisted-pair wire), is used extensively for telecommunications. These lines are used in established communications networks throughout the world for both voice and data transmission.
A coaxial cable consists of a sturdy copper or aluminum wire wrapped with spacers to insulate and protect it. This insulation minimizes interference and distortion of the signals the cable carries. Groups of coaxial cables may be bundled together in a big cable for ease of installation. These high-quality lines can be placed underground and laid on the floors of lakes and oceans. They allow high-speed data transmission and are used instead of twisted pair wire lines and high-service metropolitan areas, for cable TV system, and for short-distance connection of computers and peripheral devices. Thus, coaxial cables may be used in office buildings and other works sites for local area networks.
Fiber optics uses cables consisting of one or more hair-thin filaments of glass fiber wrapped in a protective jacket. They can conduct light pulses generated by lasers at transmission rates as high as 2 billion bits per second. This is about 10 times greater than coaxial cable and 200 times better than twisted-pair wire lines. Fiber optic cables provide substantial size and weight reductions as well as increased speed and greater carrying capacity. A half-inch diameter fiber optic cable can carry up to 50,000 channels, compared to about 5,500 channels for a standard coaxial cable. Fiber optic cables are not affected by and do not generate electromagnetic radiation therefore, multiple fibers can be placed in the same cable. Fiber optic cables have a minimal need for repeaters for signal re-transmissions, unlike electrical wire media. Fiber optics also has a much lower data error rate than other media and is harder to tap than electrical wire and cable. The biggest disadvantage of fiber optics is the difficulty of splicing the cable to make connections though this is also a security advantage that limits line tapping.
Terrestrial (earthbound) microwave systems transmit high-speed radio signals in a line-of-sight path between relay stations spaced approximately 30 miles apart. Microwave antennas are usually placed on top of buildings, towers, hills, and mountain peaks, and they are a familiar site in many sections of the country. They are still a popular medium for both long distance and metropolitan area networks.
An important data communications medium is the use of communications satellites for microwave transmission. There are several dozen communications satellites from various nations placed into stationary “parking orbits” approximately 22,000 miles about the equator. Satellites are powered by solar-panels and can transmit microwave signals at a rate of several hundred million bits per second. They serve as relay stations for communication signals transmitted from earth stations. Earth stations beam microwave signals to the satellites, which amplify and re-transmit the signals to other earth stations thousands of miles away.
Cellular radio is a radio communications technology that divides a metropolitan area into a honeycomb of cells. This greatly increases the number of frequencies and users that can take advantage of mobile phone service. Each cell has its own low-power transmitter, rather than having one high-powered radio transmitter to serve an entire city. This significantly increases the number of radio frequencies available for mobile phone service. However, this technology requires a central computer and (other communications equipment to coordinate and control the transmissions of thousands of mobile phone users as they drive from one cell to another.
Telecommunications processors such as modems, multiplexers, concentrators, front-end processors, and other devices perform a variety of support functions between the terminals and computers in a tele-communications network.
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, which 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 word “modem” is a combined abbreviation of those two words. Modems come in several forms, including small stand-alone units, plug-in circuit boards, and micro electronic modern chips.
Modems are necessary because ordinary telephone lines were primarily designed to handle continuous analog signals, such as the human voice. Since data transmissions from computers are in digital form devices are necessary to convert digital signals into appropriate analog transmission frequencies and vice versa. However, digital communications networks that transmit only digital signals are rapidly being developed. Modems that only perform (he digital/ analog conversion function are not required for such networks.
Multiplexers, Concentrators, and Controllers.
A multiplexer is a communications processor that allows a single communications channel to carry simultaneous data transmissions from many terminals. Thus, a single communications line can be shared by several terminals. Typically, a multi-plexer merges the transmissions of several terminals at one end of a communications channel, while a similar unit separates the individual transmissions at the receiving end. Devices known as concentrators and controllers have microprocessor intelligence, stored communications programs, and buffer storage. Concentrators concentrate many slow-speed lines into a high-speed line through the use of buffer storage, and they also route data to its proper destination. Controllers, or cluster controllers, link groups of terminals or other devices to a communications channel.
A front-end processor is typically a minicomputer dedicated to handling the data communications control functions for large mainframe computer systems. For example, a front-end processor uses telecommunications control programs to provide temporary buffer storage, data coding and decoding, error detection, recovery, and the recording, interpreting, and processing of control information (such as characters that indicate the beginning and end of a message). It can also poll remote terminals to determine if they have a message to send or if they are ready to receive a message.
Private Branch Exchange.
The Private Branch Exchange (PBX) is a communications processor that serves as a switching device between the telephone lines within a work area and the local telephone company’s main telephone lines, or trunks. In recent years, PBXs have become electronic, computerized devices with built-in microprocessors and stored program intelligence. They not only route telephone calls within an office but also provide other services, such as automatic forwarding of calls, conference calling, and least-cost routing of long-distance calls. Some PBX models can control communications among the terminals, computers, and other information processing devices in local area networks in offices and other work areas.
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. This software controls and supports the communications occurring in a telecommunications network. Telecommunications software packages for large computer networks are frequently called telecommunication monitors or teleprocessing (TP) monitors. Local area networks rely on software called network operating systems. Many communications software Telecommunications Software packages are also available for micro-computers.
Telecommunications software packages provide a variety of communications support services. The number and type of terminals, computers, communication processors, and communications activities involved determine the capabilities of the programs required. Several major functions can be provided.
Access control: This function-establishes the connections between terminals and computers in a network. The software works with a communications processor (such as a modem) to connect and disconnect. Communications links and establish communications parameters such as transmission speed, mode, and direction. This function may also involve automatic telephone dialing and. redialing. Logging on and off with appropriate account numbers and Security codes, and automatic answering of telephone calls from another computers.
Transmission control: This function allows computers and terminals to send and receive commands, messages, data, and programs. Some checking and correction of data transmission may also be provided. Data and programs are usually transited in the form of files, so this activity is frequently called file transfer.
Network control: This function manages communications in a telecommunications network. This software determines transmission priorities, routes (switches) messages, polls the terminals in the network, and forms waiting lines (queues) of transmission requests. It also logs statistics of network activity and resource use and detects and corrects errors.
Errors control: 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. Communications software and processors control errors in transmission by several methods, including parity checking. Parity checking involves determining whether there is an odd or even number of binary one digit in a character being transmitted or received. If a transmission error is detected, it is usually corrected by re-transmitting the message.
Security control: This function protects a communications network from unauthorized access. Access control software and other types of programs restrict access to- data and the computing resources in the network. This restriction usually involves control procedures that limit access to all or parts of a network by various categories of users. Automatic disconnection and callback procedures may also be used. Data transmissions can also be protected by coding techniques called encryption. Data is “scrambled” into a coded form before transmission and decoded upon arrival. Banks, government agencies, and others use a Data Encryption Standard as the basis for data encryption.