Wireless Technologies

• 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 miles) 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 (22,200 miles) (for geosynchronous satellites) above the equator. These Earth-orbiting systems are capable of receiving and relaying voice, data, and TV signals.

• Cellular and PCS systems – Use several radio communications technologies. The systems are divided to different geographic areas. Each area has a low-power transmitter or radio relay antenna device to relay calls from one area to the next area.

• Wireless LANs – Wireless local area network use a high-frequency radio technology similar to digital cellular and a low-frequency radio technology. Wireless LANs use spread spectrum technology to enable communication between multiple devices in a limited area. An example of open-standards wireless radio-wave technology is IEEE.

• Infrared communication can transmit signals between devices within small distances of typically no more than 10 meters. In most cases, line-of-sight propagation is used, which limits the physical positioning of communicating devices.

• A global area network (GAN) is a network used for supporting mobile communications across an arbitrary number of wireless LANs, satellite coverage areas, etc. The key challenge in mobile communications is handing off the user communications from one local coverage area to the next. In IEEE Project 802, this involves a succession of terrestrial wireless LANs.

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Wired Technologies

• 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 rated in categories which are manufactured in different increments for various scenarios.

• 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.

• ITU-T G.hn technology uses existing home wiring (coaxial cable, phone lines and power lines) to create a high-speed (up to 1 Gigabit/s) local area network.

• Optical fibre 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.

Exotic technologies

There have been various attempts at transporting data over more or less exotic media:

• IP over Avian Carriers was a humorous April fool's Request for Comments, issued as RFC 1149. It was implemented in real life in 2001.

• Extending the Internet to interplanetary dimensions via radio waves.

A practical limit in both cases is the round-trip delay time which constrains useful communication.

Computer-Networks

A computer network, often simply referred to as a network, is a collection of computers and devices interconnected by communications channels that facilitate communications and allows sharing of resources and information among interconnected devices. Computer networking or Data communications (Datacom) is the engineering discipline concerned with the computer networks. Computer networking is sometimes considered a sub-discipline of electrical engineering, telecommunications, computer science, information, technology and/or computer engineering since it relies heavily upon the theoretical and practical application of these scientific and engineering disciplines.

Networks may be classified according to a wide variety of characteristics such as medium used to transport the data, communications protocol used, scale, topology, organizational scope, etc.

A communications protocol defines the formats and rules for exchanging information via a network. Well-known communications protocols are Ethernet, which is a family of protocols used in LANs, the Internet Protocol Suite , which is used not only in the eponymous Internet, but today nearly ubiquitously in any computer network.

Study Tips

"One way to study is to sing the information. Another way is to think that the information you want to study is written in your mind in different colors. If you make a cover of your favorite magazine for your text book you will pay more attention to your textbook."

Avoid all distractions and don't study when you are tired. Relax with something light and then come back to study. Don't confuse laziness with tiredness.

1. Have a time table for better focus; 2.Study for a stretch of one hour each session and take breaks; 3.Write or jot notes. What is written can sometimes be easliy remembered; 4.Write a summary of the passage or chapter to reinforce better understanding; 5.Test yourself on a few questions to check understanding. This will reveal parts of a passage or chapter where more time should be spent or where your notes need revision; 6.Last but not least, studying is hard work. Hence, be prepared to work hard. No worthy certificate or qualification will come easily.

Think positively about studying, be goal directed, know what you want at the end of the day, know your deadlines, and take practice tests to help you understand what you have studied.

Ask your teachers questions. I ask questions in class whenever I don't understand something. This does two things. First, I get the help I need. Second, it shows the teacher that I'm interested and trying. You want your teachers to have a good opinion of you. It can help your grade.