Telecommunication system
A telecommunication system consists of hardware and software that transmits information from one location to another. These systems can transmit text, data, graphics, voice, documents or full-motion video information. The major components of a telecommunication system include the following.
Hardware-Includes all types of computer (e.g., desktop, server, main frame) and communication processors.
Communication media- the physical media through which electronic signals are transmitted, including wireless media.
Communication networks-the links among computers and communications devices.
Communication software- software that controls the telecommunication system and the entire transmission process.
Data communication providers: regulated utilities are private firms that provide data communication services.
Communication protocols -the rules for transmitting information across the system.
Communication supplication –electronic data interchange teleconferencing, videoconferencing, electronic mail, facsimile and electronic funds transfer, as well as others.
The system must do all of the following: transmit information; establish the interface between the sender and the receiver; rout messages along the most efficient paths; ensure that right message gets to the right receiver; check the message for errors and rearrange the format if necessary; convert messages one speech to another (computers are usually faster than a communication medium); ensure that the sending devices, receiving devices and communication links are operational (in words, maintain the network); and secure the information at all times.
Signals:
Telecommunications media carry two basic types of signals, analog and digital. Analog signals are continuous waves that transmit information by altering the characteristics of the waves. Analog signals have two parameters, amplitude and frequency.
Digital signals do not have the characteristics “wave” shape that analog signals do. Rather, they are discrete pulse that is either on or off. This quality allows them to convey information in a binary form that can be clearly interpreted by computers.
Communication processors:
Communications processors are hardware devices that support data transitions and receptions across a telecommunication system. These devices include modems, multiplexers, front – end processors, and concentrators.
Modem:
The conversion from digital to analog is called modulation, and the reverse demodulation. The device that performs these two processors is called a modem, a contraction of the terms modulates/demodulate. A modem’s transmission speed is measured in bytes per seconds (bps). Typical modem speeds range from 14,400 to 56,600 bps.
Multiplexer:
A multiplexer is an electronic device that allows a signal communications channel to carry data transitions simultaneously from many sources. Multiplexers lower communication cost by allowing devices to share communication channels.
Front-end processors:
With most computer, the center processing unit (CPU) must communicate with several computers at the same time. Routine communication task can absorb a large proportion of the CPU’s processing time. In order not to waste valuable CPU time, many computer systems have a small secondary computer dedicated solely to communication known as front-end processor, this specialized computer manager all routing communication with peripheral devices. The functions of a front-end processor include coding and decoding data; deducting errors; and recovering, recording, interpreting and processing the control information that is transmitted.
Communication media and channels:
For data to be communicated from one location to another, some form of pathway or medium must be used. These path ways are called communications channels, and they include twisted – pair wire, coaxial cable, fiber optics cable, microwave transmission, and satellite transmission.
Cable media:
Cable media use physical wires or cables to transmit data and information. There are three types of cable media: twisted pair wire, coaxial cable, and fiber optic cable. Twisted-pair wire and coaxial cable are made of copper and fiber optic cable is made of glass.
Twisted pair wire:
Twisted pair wire is the oldest and still the most prevalent form of communication wiring. Twisted pair wire consists of two insulated copper wires, typically about 1 mm thick. The wires are twisted together in a helical form, just like a DNA molecules. The purpose of twisting a wire is to reduce electrical interference from similar pairs close by. The most common application of the twisted pair is the telephone system. A twisted pair connects nearly all telephones to the telephone company office. Twisted pair can run several kilometers without amplification, but for longer distances repeaters are needed. It is relatively inexpensive to purchase, widely available, and easy to work with, and it can be made relatively unobtrusive by running it inside walls, floors and ceilings. However, twisted-pair wire has some significantly disadvantages. It emits electromagnetic interference, is relatively slow for transmitting data, is subject to interference from the electrical source, and can be easily “taped” for gaining unauthorized access to data by unintended receivers.
Coaxial cable:
A coaxial cable consists of a stiff copper wire as the core surrounded by an insulating material. A cylindrical conductor encases the insulator, offer as a closely woven braided mesh. The outer conductor is covered in a protective plastic sheath. It has better shielding than twisted pairs, and can carry much more data for longer distances at higher speeds. Coaxial cable can cost from 10 to 20 times more than twisted pair wire. Also, because of its flexibility, it can increase the cost of installation or re-cabling when must be moved.
Data transmission over coaxial cable is divided in to two basic types: base band transmission- transmission is analog, and each wire carries only one signal at a time.
Broad band transmission – transmission is digital, and each wire can carry multiple signals simultaneously.
Fiber optic cable
Fiber optics cable consists of thousands of very thin filaments of glass fibers that conduct light pulses generated by lasers at very high speed transmission frequencies. Cladding, a coating that prevents a light from leaking out of the fiber, surrounds the fiber optics. An optical transmission system has thus three components: the light source, the transmission system and the detector. Conventionally, a pulse of light indicates a 1 bit and the absence of light indicates a zero bit. The ultra thin fiber of glass is the transmission medium. The detector generates an electrical pulse when light falls on it. By attaching a light source to one end of the optical fiber and a detector to the other, we have a unidirectional data transmission system that accepts an electrical signal, converts and transmits it by light pulses, then reconverts the outputs in to electrical signal at the receiving end. A signal glass fiber can carry more than 30,000 simultaneous telephone calls, compared to about 5,500 calls on a standard copper coaxial cable. Optical fiber as a proven performance a data transmission rates of 2.5 million bites (giga bits) per second.
Optical networking
Optical networking increase fiber optic capacity by adding 16, 32 or up to 80 additional wavelengths to a signal piece optic filament. The key to an optical network is that signals coming in to the network are converted immediately to colors of light and are not converted immediately to colors of light and are not converted to electrical signals. At this time, there are no defined limits to how much bandwidth a signal fiber hold.
Wireless media
The key of mobile communications in today’s rapidly moving society is data transmission over electromagnetic media – the “air waves”. Common wireless data transmission include microwaves transmission include microwaves transmission, communication satellite, pages, cellular phones, mobiles data networks, personal communications services, and personal digital assistants.
Microwave:
Microwaves systems are widely used for high-volume, long-distance, point-to-point communication. Microwaves owner can usually not be spaced more than 30 miles apart because the earth’s curvature would interrupt the sight from tower to tower. To minimize line of sigh problem, microwaves antennas are usually placed on top of buildings, towers and mountains peak. Long-distance telephone carrier use microwave systems because they generally provide about ten times the data-carrying capacity of wire. Microwave transmissions are susceptible to environmental interference during severe whether such as heavy rain or snowstorms. Microwave also relatively inexpensive.
Satellite
A major advance in communication in recent year is the use of communication satellites for digital transmissions. As with microwave transmission satellites must receive and transmit via line of sight. However, the enormous footprint of satellite’s coverage area from high altitudes overcomes the limitations of microwaves data relay station. Currently, there are three types of orbits in which satellite are placed: geostationary earth orbit, medium earth orbit and low earth orbit.
A global positioning system (GPS) is a wireless system that uses satellites to enable users to determine their position anywhere on the earth. GPS equipment has been used for navigation by commercial airlines and ships. 24 satellites that are shared worldwide support GPS. Each satellite orbits the earth once in 12 hours, on the precise path at an altitude of 10,900 miles.
Radio
Radio electromagnetic data communications do not have to depend on microwave or satellite links, especially for short ranges such as within an office setting. Radio is being used increasingly to connect computers and peripherals equipments or computers and local area networks. For data communications the greatest advantage of radio is that no metallic wires are needed. Radio waves tend to propagate easily through normal office walls. Radio waves also are Omni directional. Meaning that they travel in all directions from the source, so that the transmitter and receiver do not have to be carefully aligned physically. The devices are fairly inexpensive and easy to install. Radio also allows for high data transmission speeds.
Infrared
Infrared light is red light not commonly visible to human eyes. It can be modulated or pulsed for conveying information. The most common application of infrared light in television or video cassette recorder remote control units. With computers and local area networks. Many portable PC’s can bring with infrared ports, which are handy when cable connection with a peripheral (such as a printers or modem) is not practical.
Disadvantages
Signals are not secure there are available to all receivers with in the footprint, intended or not. Some frequencies are susceptible to interference from bad weather or ground based microwaves signals.