Types of transmission media II Transmission media

 Transmission media 

Data in communication system is transferred through signals. Signals are transmitted in the form of electromagnetic energy from one device to another. An electromagnetic signal is series of electromagnetic energy pulses at various frequencies. These signals can be transmitted through copper wires, optical fibers, atmosphere, water and vacuum. Different Media have different properties like bandwidth, delay, cost and ease of installation and maintenance. 

Thus, transmission media also known as communication channel is the physical path or electronic roadway through which data or signal can be transmitted from one point to another (sender to receiver). 

There are two types of transmission media used in computer system. They are: 

• Guided or bounded Transmission media 
• Unguided or unbounded transmission media 

1. Guided or bounded transmission media 

Guided or bounded transmission media are the physical cables through which signals are confined to narrow path. These media are made up of external conductor (Usually copper) bounded by jacket material. They offer high speed, good security and low cost. However, some time they cannot be used due to distance communication. Three common types of guided media are used for data transmission. They are: 

• Coaxial Cable (CC) 
• Twisted Pairs Cable (TPC) 
• Fiber Optics Cable (FDC) 

a. Coaxial cable: 

Coaxial cable is very common and widely used communication mode. It contains two conductors that are parallel to each other. The center conductor in the cable is usually copper. Outside this central conductor is a non-conductor 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 from Electro Magnetic Interference. The examples of coaxial cable is: Television wire. 

Characteristics of coaxial cable are 

• Coaxial cable is inexpensive. 
• Coaxial cable is easy to wire. 
• Coaxial cable is easy to expand. 
• Moderate level of coaxial cable is EMI resistance. 

b. Twisted Pair Cable 

The most popular network cabling is twisted pair cable. It is light weight, easy to install, inexpensive and support many different types of network. Twisted pair cabling is made of pairs of solid or stranded (trapped) copper twisted along each other. The twists are done to reduce dependently to EMI and cross talk. The number of pairs in the cable depends on the type. There are two types of twisted pair cabling. 

i. Unshielded Twisted Pair (UTP) 

Unshielded twisted pair is more common types of guided media. It can be either voice grade or data grade depending on the condition. 

Characteristics of unshielded twisted pair: 

• Unshielded twisted pair is with low cost. 
• Unshielded twisted pair is easy to install. 
• Unshielded twisted pair has high speed capacity. 
• Unshielded twisted pair contains high attenuation (reduction). 

ii. Shielded Twisted Pair (STP) 

Shielded twisted pair cable is such type of guided media which is similar to unshielded twisted pair cable The major deference is that it has a mesh shielding that protects it from EMI which allows for higher transmission rate. 

Characteristics of Unshielded Twisted Pair: 

• Shielded Twisted Pair is medium in cost. 
• Shielded Twisted Pair is easy to install. 
• Shielded Twisted Pair has higher capacity than UTP. 
• Shielded Twisted Pair is medium immunity from EMI. 

c. Fiber Optics cable 

Fiber optic cable uses electronic signals such as light to transmit data. In fiber optic cable light only moves in one direction for two way communication to take place a second connection made between the two devices. It is actually two stands of cable. Each stand is responsible for one direction of communication. A laser at one device sends pulse of light through this cable to other device. In the center of fiber cable is a glass stand or core. The light from the laser moves through this glass to the other device around the internal core which is a reflective material known as cladding (covering/protecting). 

Characteristics of fiber optic cable: 

• Fiber optic cable is expensive cable. 
• Fiber optic is very hard to install. 
• Fiber optic is extremely high speed. 
• Fiber optic is extremely low attenuation. 
• Fiber optic has no EMI interference. 

2. Unguided or unbounded transmission media 

Unguided transmission media also known as unbounded media transport electromagnetic waves without using a physical conductor. In this type of communication, the signals are normally broadcast through free space and thus are available to anyone who has a device capable of receiving them. Some of the common unguided media are discussed below. 

a. Microwave System 

Microwave systems transmit high-speed radio signals in a line of sight path between relay station i.e. transmission from one antenna to another usually placed on top of buildings, towers, hills and mountains peaks. Microwave system transmits high-speed signals in a line of sight path relay stations spaced approximately 25 to 35 miles apart. 

b. Communication Satellite 

Communication satellites have now become an integral part of the worldwide communication system. The satellites have the capability of a direct line of sight path and almost he earth's entire surface. So, they can transmit high speed microwave or radio-signal to the transmitters on the ground (earth). A ground station on one side of the ocean transmits a signal to the satellite. This then sends the signal to a ground station on the other side. A single satellite usually contains multiple transponders device that consists of a radio receiver and transmitter that operates independently typically six to twelve. Each transponder uses a different radio frequency, making it possible for multiple communications to proceed simultaneously. 

c. Infrared 

Infrared is wireless system limited to a small area usually requires that the transmitter be pointed tower the receiver. Infrared hardware is inexpensive compared to other mechanism. Computer networks can be use infrared technology for data communication. Infrared systems are especially convenient for small portable computers because infrared offers the advantages of wireless communications without requiring the use of antennas. 

d. Bluetooth 

Bluetooth technology enables short-range wireless connections between computers and devices like desktop, notebook, handheld, personal digital assistants, mobile phones, camera phones, printers. digital cameras, headsets, keyboards and even a computer mouse. Bluetooth wireless technology uses a globally available frequency band 2.4 Ghz for worldwide compatibility with the 10 meter range. 

e. Wi-Fi

Wireless Fidelity is a type of wireless network technology used for connecting computers and other devices to the computer network and Internet. The frequencies Wi-Fi works at are 2.4 Ghz or 5 GHz, ensure no interference with cellphones, broadcast radio, TV antenna etc. The two-way radios are encountered during transmission in Wi-Fi system.