Every bit which transformed from one place to another required some type of communication media. Physical layer of OSI Model is dedicated to the transmission media.
Types of Transmission Media
• Guided Media
• Unguided Media
Guided media are those which provide a conduit from one devices to another. With guided media, the electromagnetic waves representing the data signals are guided along a physical path. Guided media include the following. :-
• Co – axial cables
• Twisted Pair cables
• Optical Fiber
Co-axial Cable :- Coaxial cabling is the primary type of cabling used by the cable television industry and is also widely used for computer networks. Coaxial cable is difficult to run and is generally more expensive than twisted pair cable. However, it provides a tremendous amount of bandwidth and is not as susceptible to outside interference as is UTP.
It consists of four primary components, as follows:
- A core consist of copper wire which server as the primary channel.
- An insulating sheathes which encloses inner core conductor to separate both inner and outer conductor from each other.
- A braided copper/aluminum sheath beneath the insuLatoWebr. This is used to protect from external electromagnetic interference.
- The last layer, which is made of Teflon or plastic coating, To prevent dirt and moisture attacking the cable, and prevent the coax cable from being damaged by other mechanical means .
Advantages and Disadvantages of Coaxial Cable
- Can carry multiple frequency range to support multiple channel.
- Lower error rates.
- Signal can travel to long range without amplifier.
- High bandwidth.
- Greater protection from external interference.
- Installation cost low compare to twisted pair because connectors take less time to apply.
- The thicker the cable, the more difficult to work with.
- High performance with TV transmission, Low performance with Computer Network.
- It is more expensive than twisted pair.
Twisted pair consist of a pair of insulated wires which are twisted to each other. The twists help to cancel out the electromagnetic interference (EMI) generated by voltage used to send a signal over the wire. The interference can cause problems, called crosstalk, for adjacent wire pairs.
Twisted pair is two types:-
UTP and STP
Unshielded Twisted Pair(UTP) :- UTP is cost effective and simple to install, and its bandwidth capabilities are continually being improved. UTP cabling typically has only an outer covering (jacket) consisting of some type of nonconducting material. This jacket covers one or more pairs of wire that are twisted together.
Shielded Twisted Pair(STP):- STP cable is less susceptible to outside electromagnetic interference(EMI) than UTP cabling because all cable pairs are well shielded.
Advantages and Disadvantages of Twisted Pair
- Cheap and easy to install
- Better protection from electrical interference.
- Noise immunity is low
- STP wire is more expensive than twisted pair wire.
- STP is difficult in installation.
- Low Bandwidth
Optical Fiber is a network transmission media that use glass, plastic, fiber to transmit network data in the form of light pulses. Optical Fiber transmissions encode the ones and zeroes of a digital network transmission by turning on and off the light pulses of a laser light source, of a given wavelength, at very high frequencies. The light source is usually either a laser or some kind of light-emitting diode (LED). The light from the light source is flashed on and off in the pattern of the data being encoded. The light travels inside the fiber until the light signal gets to its intended destination and is read by an optical detector. Fiber-optic cables are optimized for one or more wavelengths of light. As show on figure below.
Advantages and Disadvantages of Optical Fibre
- Immunity to electromagnetic Interference(EMI) :- Fiber-optic cabling is immune to EMI because optical fiber does not conduct electricity and uses light signals in a glass fiber, rather than electrical signals along a metallic conductor,to transmit data. So it cannot produce a magnetic field and thus is immune to EMI.
- Higher data rates :- Data rates exceeding the gigabit per second (Gbps) range and higher.
- Longe Distance :- Because Optical Fibre immune from the EMI problems of traditional copper cabling and because they don’t use electrical signals that can degrade substantially over long distances, single-mode Optical Fibre cables can span distances up to 75 kilometers without using signal-boosting repeaters.
- Security :- It prevent eavesdropping.
- High Bandwidth :- Optical cables have a much greater bandwidth than metal cables.
- Low weight
- Higher cost
- Difficult to installation :- It require high level of skilled people with special devices for installation.
Unguided Media - In unguided media communication devices sends and receives data through air, vacuum and water. It uses electromagnetic waves to sends or receives data. Unguided media means that to transmit data signals but without following specific path. This type of network is used when there is no possibility to reaching of cable media in that location. All unguided media transmission are classified as wireless transmission.
Infrared (IR) transmissions are signal transmissions that use infrared radiation as their transmission medium. It has a wavelength shorter than visible light with more energy. Infrared is a very popular method of wireless networking. Infrared transmissions allows computing devices to communicate via short-range wireless signals. Frequency range from 100GHz to 1,000THz.
Advantages and Disadvantages of Infrared Transmission
- Low Cost :- Infrared equipment is relatively inexpensive when compared to other wireless methods like microwave or radio frequency (RF).
- High bandwidths :- Point-to-point infrared transmissions support fairly high (around 1.544Mbps) bandwidths. They are often used as WAN links because of their speed and efficiency.
- Easy to Install :- Installation of infrared devices is very simple.
- High security on point-to-point connections :- Because point-to-point infrared connections are line of sight and any attempt to intercept a point to- point infrared connection will block the signal,The signal can’t be intercepted without the knowledge of the sending equipment.
- Portability :- Infrared transceivers and equipment are usually small and have lower power requirements. Thus, these devices are great choices for portable, flexible networks.
- Line of sight needed for focused transmissions :- Infrared transmissions require an unobstructed path between sender and receiver.
- Weather attenuation :- Infrared transmissions travel through the air, any change in the air can cause degradation of the signal over a distance. Humidity, temperature, and ambient light can all negatively affect signal strength in low-power infrared transmissions. In outdoor, higher power infrared transmissions, fog, rain, and snow can all reduce transmission effectiveness.
Radio-Frequency (RF) Transmission
Radio-frequency (RF) transmission systems are those network transmission systems that use radio waves to transmit data. Many companies are installing RF access points in their networks to solve certain mobility issues. The relatively low cost and ease of installation of RF systems play a part in their popularity. Its frequency is between 10 kHz to 1GHz.
Advantages and Disadvantages of Radio Frequency(RF) Transmission
- No needed line of sight :- Radio waves can penetrate walls and other solid obstacles, so a direct line of sight is not required between sender and receiver.
- Low cost :- Radio transmitters have become extremely cheap to manufacture.
- Easily eavesdropping :- Since RF signals are broadcast in all directions, it is very easy for someone to intercept and interpret a LAN transmission without the permission of the sender or receiver.
- RF interference :- RF signals can interfere with the proper operation of an RF-transmission LAN.
- Limited range :- RF systems don’t have the range of satellite networks
Microwave Transmission use powerful, focused beams of energy to send communications over long distances. Microwave uses line-of-sight transmission through space. It mainly used for unicast communication.
There are 2 types of Microwave Transmission :
- Terrestrial Microwave
- Satellite Microwave
Terrestrial microwave typically use directional parabolic antennas to send and receive signals in the lower gigahertz frequency range. The signals are highly focused and must travel along a line-of-sight path. It frequency range from 4 to 6 GHz and 21 to 23 GHz with capacity range form 1 to 100 Mbps.
Satellite microwave transmit signals between directional parabolic antennas. satellite microwave systems can reach the most remote places on earth and communicate with mobile devices. It frequency range from 11 to 14 GHz with capacity range form 1 to 10 Mbps.
Advantages and Disadvantages of Microwave Transmission
- Very high bandwidth :- Microwave have the high bandwidth because of the high power of the transmission systems. Speeds of 100Mbps and greater are possible.
- Transmissions travel over long distances :- It can travel very long distance from few kilometer to thousand kilometer.
- Point-to-point or broadcast signals :- The signals can be focused tightly for point-to-point communications, or they can be diffused and sent to multiple locations via broadcast communications.
- Expensive :- Microwave transmission and reception equipment is the most expensive of all the types of wireless transmission equipment.
- Line-of-sight required :- Microwave transmission require a line-of-sight between sender and receiver.
- Atmospheric attenuation :- Atmospheric conditions can negatively affect microwave transmissions.
- Propagation delay :- Propagation delay is very high in satellite microwave.
- Safety :- Due to high power of microwave beam it can pose a danger to human or animal.
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