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Data communication is the active process of transporting data from one point to another. Networks are communication system designed to convey information from a point of origin to a point of destination. Note that they are communication system, not computer system. The operative word is communication, the transfer of information from one device to another.
Networks come in two flavors – local as in local area network, which cover a small area and have a finite, relatively small, number of users and global or long-haul, which cover long distance and have an unlimited number of users. Telephone networks are long network. It refers to the transmission of the digital signals over a communication channel between the transmitter and receiver computers. Communication is possible only with wired and wireless connectivity of the computers with each other.
The effectiveness of a data communication system depends on three fundamental characteristics:
- Delivery: The system must deliver data to the correct destination. Data must be received by the intended device or user and only by that device or user.
- Accuracy: The system must deliver data accurately. Data that have been altered in transmission and left uncorrected are unusable.
- Timeliness: The system must deliver data in a timely manner. Data delivered late are useless. In the case of video, audio and voice data, timely delivery means delivering data as they are produced, in the same order that they are produced, and without significant delay. This kind of delivery is called real-time transmission.
Data Communication Component
The following are the basic components for working of a communication system.
Data Communication Components
The transmitter sends the message and the receiver receives the message. The medium is the channel over which the message is sent and the protocol is the set of rules that guides how the data is transmitted from encoding to decoding. The message of course is central to all the components. The message is the data that is being communicated.
Transmitter: The transmitter is the device that sends the message. It can be a computer, workstation, telephone handset, video camera, and so on.
Receiver: The receiver is the device that receives the message. It can be a computer, workstation, telephone handset, television, and so on.
Medium: The transmission medium is the physical path by which a message travels from sender to receiver. It can consist of twisted pair wire, coaxial cable, fiber-optic cable, laser or radio waves (terrestrial or satellite microwave).
Message: The message is the transmission (data) to be communicated. It can consist of text, number, pictures, sound, or video or any combination of these.
Protocol: A protocol is a set of rules that governs data communication. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating, just as a person speaking German cannot be understood by a person who speaks only Japanese.
Following are the major communication devices which are frequently used:
- Wire Pairs: Wire pairs are commonly used in local telephone communication and for short distance digital data communication. They are usually made up of copper. Using these wire pairs data transmission speed is normally 9600 bits per second in a distance of 100 metre.
- Twisted pair: Twisted pair wire is the most widely used medium for telecommunication. Twisted-pair cabling consist of copper wires that are twisted into pairs. Ordinary telephone wires consist of two insulated copper wires twisted into pairs. Computer networking cabling (wired Ethernet as defined by IEEE 802.3) consists of 4 pairs of copper cabling that can be utilized for both voice and data transmission. The use of two wires twisted together helps to reduce crosstalk and electromagnetic induction. The transmission speed ranges from 2 million bits per second to 10 billion bits per second. Twisted pair cabling comes in two forms which are Unshielded Twisted Pair (UTP) and Shielded twisted-pair (STP) which are manufactured in different increments for various scenario.
- Coaxial cable: Coaxial cable is widely used for cable television systems, office buildings, and other work-sites for local area networks. The cables consist of copper or aluminum wire wrapped with insulating layer typically of a flexible material with a high dielectric constant, all of which are surrounded by a conductive layer. The layers of insulation help minimize interference and distortion. Transmission speed range from 200 million to more than 500 million bits per second.
- Optical fiber: Optical fiber cable consists of one or more filaments of glass fiber wrapped in protective layers that carries data by means of pulses of light. It transmits light which can travel over extended distances. Fiber-optic cables are not affected by electromagnetic radiation. Transmission speed may reach trillions of bits per second. The transmission speed of fiber optics is hundreds of times faster than for coaxial cables and thousands of times faster than a twisted-pair wire. This capacity may be further increased by the use of colored light, i.e., light of multiple wavelengths. Instead of carrying one message in a stream of monochromatic light impulses, this technology can carry multiple signals in a single fiber.
- Terrestrial microwave: Terrestrial microwaves use Earth-based transmitter and receiver. The equipment looks similar to satellite dishes. Terrestrial microwaves use low-gigahertz range, which limits all communications to line-of-sight. Path between relay stations spaced approx, 48 km (30 mi) apart.
Microwave antennas are usually placed on top of buildings, towers, hills, and mountain peaks.
- Communications satellites: The satellites use microwave radio as their telecommunications medium which are not deflected by the Earth’s atmosphere. The satellites are stationed in space, typically 35,400 km (22,000 mi) (for geosynchronous satellites) above the equator. These Earth-orbiting systems are capable of receiving and relaying voice, data, and TV signals.
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