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Реферат: Network Mediums Essay Research Paper With the

Название: Network Mediums Essay Research Paper With the
Раздел: Топики по английскому языку
Тип: реферат Добавлен 22:57:20 01 ноября 2010 Похожие работы
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Network Mediums Essay, Research Paper

With the emergence of the Ethernet LAN (Local Area Network) introduced in the early 1970’s by Xerox, the telecommunications world has welcomed this newfound gift with open arms. Since communications is such a vital aspect of all businesses these days, proper acquaintance with this marvelous technology can greatly enhance your company’s productivity and efficiency. In this paper, we will reflect into the many different characteristics of media that the LANs are based upon and compare/contrast these different medias.

There are basically four types of media used for Local Area Networks. The most commonly used are twisted copper pairs, Coaxial cables, Fiber Optic, and the Wireless technology.

Twisted copper wire, also known, as the common telephone wire is very similar to the wires used in telephone systems. However, the twisted pair wire required for reliable data transmission is of a heavier gauge than the telephone wire. It uses 24 to 26 AWG (American Wire Gauge, www.datapro.com). The purpose of twisting the copper wires together is to minimize the interference between the two adjacent wires. Otherwise, there would be too much line noise to transfer voice or data efficiently. There are two different types of twisted pairs that are used to transmit data. The STP (Shielded Twisted Pair) and the UTP (Unshielded Twisted Pair). Just like it sounds, the STP is a special kind of copper telephone wiring used in some business installations. An outer covering or a shield is added to the twisted pair acting as a ground. This process shields the twisted pair from EMI (Electro-magnetic Interference), which will disturb the data transmission greatly. The UTP is just a twisted pair without the extra shielding. It just relies on the copper twists to protect it from the EMI. The twisted pairs are grades into five different categories by their data carrying ability. The 6th grade is still in the works. (Please refer to the diagram below: www.whatis.com)

Category Maximum data rate Usual application

CAT 1 Less than 1 Mbps Analog voice (plain old telephone service)ISDN Basic Rate InterfaceDoorbell wiring

CAT 2 4 Mbps Mainly used in the IBM Cabling System for Token Ring networks

CAT 3 16 Mbps Voice and data on 10BASE-T Ethernet

CAT 4 20 Mbps Used in 16Mbps Token RingOtherwise not used much

CAT 5 100 Mbps 100 Mbps TPDDI155 Mbps ATM

As you can see, the twisted pairs can range greatly in bandwidth by the different levels of CATs. For a LAN environment, the CAT 2 and above are used because they can transmit greater amounts of data. These generally are used for Token Ring LANs except for the CAT 3, which is only supported by the Ethernet LANs. Most companies who have networks in the offices use twisted pair system to run their LAN. Using the twisted pair media for LANs is very attractive because of its low cost; mainly the UTP setup because it cost much less than the STPs and the STP cabling are far more difficult to put into walls than the UTPs. On the other hand, the risk of going with the twisted pair setup is the instability of the data flow because it’s susceptibility to line interference.

The coaxial cabling is known as the “Original LAN Media” (www.datapro.com). The Coaxial cable is similar to the copper wires with the exception that one wire is braided or solid sheath that encompasses the other wire. Insulation material separates the two wires, the center wire is at high signal level, and the shield wire is at ground potential. The grounding of the outer shielding wire means that interference cannot penetrate the coaxial cable and induce noise onto the circuit. Shielded also do not radiate signals to other circuits as non-shielded circuits. The coaxial media also has two variations. The “thick” Ethernet, which runs on RG-8 coaxial cabling with a diameter of 0.4” and the “thin” Ethernet, which uses RG-58 coaxial cable with a diameter of 0.25”. (www.datapro.com). Using a coaxial cable provides a much larger analog bandwidth and digital transmission speed. Also the attenuation per mile is much grater than twisted-pair circuits. Along with the added features versus the twisted pair, the coaxial cabling does cost significantly more.

Fiber optic media can be considered to be the best media available for LANs. Fiber optic is also the primary transmission in FDDI (Fiber Distributed Data Interface: The Irwin Handbook of Telecommunications, page 658). This amazing type of media transmits data by the use of light impulses. The pulses are traveled through the optical casing made up of either glass or plastic fiber. The most attractive feature of this particular media is that it is capable of unlimited transmission speeds. Along with the mind-boggling bandwidth, fiber optic media is virtually immune to all electrical and electromagnetic interferences, meaning it will carry the data to its destination without losing a single bit of data along the way. The two types of fiber optic media that are commonly used are the single mode and the multimode fiber. As the single mode fiber requires a laser as the light source to transmit data over long distances, the multimode fiber uses LEDs (light emitting diodes) as the light source. Few discouraging aspects of the fiber optic media are the high cost of equipment and extremely difficult installation process. For example: Attaching a connector requires the polishing of each fiber end and must be precisely aligned with the media. Because of such complicated method, the fiber optic media is used readily only for backbone LANs. Recently, new developments have risen, enabling easier method of installation for this media. However the widespread implementation of this media is still sluggish.

Wireless media for LANs is the newest technological advancement in the area of data transmission. With mobility being its driving force, it is also one of the top growth areas in telecommunications today. But questions do arise regarding data integrity when being transmitted. In wireless media, there are three different types of LANs. They are Infrared, Microwave, and the SST (Spread Spectrum Technology)(refer to the chart on page 6; www.datapro.com, Wireless LAN). Most of us are familiar with the Infrared technology. We use it everyday in our homes such as Television remote controls. Infrared signals can be transmitted in two different manners. The laser method compresses the beam so it can be easily modulated allowing it to transmit data up to 16 Kilometers. LEDs are another method for transmission of Infrared signals. The LEDs have much less intensity than the lasers but are relatively easy and inexpensive to implement. The range is also much shorter than the laser. The Infrared media is very seldom used because it is only effective to the line of sight. Any obstructions in the line of sight will result in termination of data transmission.

The microwave media resides on the spectrum between radio waves and infrared. It is capable of higher frequencies than lower down ate the point where the SST is found. Microwave media can transmit data at higher speeds compared to its wired counterparts, but only through Ethernet or Token Ring LANs. Even though microwaves can transfer data at 18GHz to 19GHz, it also is seldom use for LAN technology of it numerous FCC regulations you must comply with just to use it. Because it can interfere with other modes of transmission, you’ll be subjected to FCC regulations such as proper licensing and radius limitations. Not to mention the outrageous cost accompanying this method of media. The last type of wireless media available is the SST. This technology originally was developed as an anti-jamming, interference immune communications method during the World War II. SST is fairly immune to the noise and is very secure. However, there are issues when using omni-directional antennae such as attenuation loss or traveling through reinforced concrete. In order to overcome these types of obstacles, directional antennae must be placed if signal needs to travel more the 10 Kilometers. This media is also a turn off to many because of its high cost and the complexity of implementation. The antennae installed must be precise in its direction; the slightest deviation will result in failure of signal transmission. Generally, large corporations employ these media to interconnect LANs between buildings to bypass the local telephone company.

Technology Spread Spectrum Narrowband Microwave Infrared

Maximum Coverage 105 to 800 feet, or up to 50,000 square feet 40 to 130 feet, or up to 5,000 square feet 30 to 80 feet

Line of Sight Required No No Yes

Transmit Power Less than 1W (U.S.) or 100mW (Europe) 25mW Does not apply

License Required No Yes No

Inter-building Use Possible with unidirectional antenna No Possible

Rated Speed (percent of 10 Mbps wire) 20 to 50 (most versions available) 33 50 to 100

Bibliography

www.whatis.com

www.datapro.com

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