Transmission Media The means through which data is transformed from one place to another is called transmission or communication media. There are two categories of transmission media used in computer communications. - Bounded/Guided Media - Uubounded/Unguided Media Bounded Media Bounded media are the physical links through which signals are confined to narrow path. These are also called guide media. Bounded media are made up o a external conductor (Usually Copper) bounded by jacket material. Bounded media are great for LABS because they offer high speed, good security and low cast. However, some time they cannot be used due distance communication. Three common types of bounded media are used of the data transmission. These are - Coaxial Cable - Twisted Pairs Cable - Fiber Optics Cable Coaxial Cable Coaxial cable is very common & widely used commutation media. For example TV wire is usually coaxial. 1 / 8
Coaxial cable gets its name because it contains two conductors that are parallel to each other. The center conductor in the cable is usually copper. The copper can be either a solid wire or stranded martial. Outside this central Conductor is a non-conductive material. It is usually white, plastic material used to separate the inner Conductor form the outer Conductor. The other Conductor is a fine mesh made from Copper. It is used to help shield the cable form EMI. Outside the copper mesh is the final protective cover. (as shown in Fig) The actual data travels through the center conductor in the cable. EMI interference is caught by outer copper mesh. There are different types of coaxial cable vary by gauge & impedance. Gauge is the measure of the cable thickness. It is measured by the Radio grade measurement, or RG number. The high the RG number, the thinner the central conductor core, the lower the number the thicker the core. Here the most common coaxial standards. - 50-Ohm RG-7 or RG-11 : used with thick Ethernet. - 50-Ohm RG-58 : used with thin Ethernet - 75-Ohm RG-59 : used with cable television - 93-Ohm RG-62 : used with ARCNET. Characteristics of Coaxial Cable - Low cost - Easy to install - Up to 10Mbps capacity - Medium immunity form EMI - Medium of attenuation 2 / 8
Advantages - Inexpensive - Easy to wire - Easy to expand - Moderate level of EMI immunity Disadvantages - Single cable failure can take down an entire network Twisted Pair Cable 3 / 8
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- Medium cost - Easy to install - Higher capacity than UTP - Higher attenuation, but same as UTP - Medium immunity from EMI - 100 meter limit Advantages of STP: - Shielded - Faster than UTP and coaxial Disadvantages of STP: - More expensive than UTP and coaxial - More difficult installation - High attenuation rate Fiber Optics 5 / 8
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