“You can have data without information, but you cannot have information without data”– Daniel Keys Moran
Communication Channels provide a path to transfer data from one system to another. There are different nature of mediums by which data is transferred, we will learn them here.
Data can be transferred by either physical cable systems or travel by air. We will understand these mediums, their advantages and disadvantages.
Note : – This post is continuation of our Data Communication Concept | 2020 series. Click on the link to learn complete course.
Classification of Communication Channels by Nature of the Medium
Various transmission media can be used for transfer of data. These transmission media may be of two types −
1. Guided Medium – In guided media, transmitted data travels through cabling system that has a fixed path. For example, copper wires, fibre optic wires, etc.
2. Unguided Medium – In unguided media, transmitted data travels through free space in form of electromagnetic signal. For example, radio waves, lasers, etc.
Each transmission media has advantages and disadvantages based on bandwidth, speed, delay, cost per bit, ease of installation and maintenance, etc.
1. Twisted Pair Cable
A twisted pair cable comprises of two separate insulated copper wires, which are twisted together and run in parallel. The copper wires are typically 1mm in diameter. One of the wires is used to transmit data and the other is the ground reference.
To reduce this electromagnetic interference, pair of copper wires are twisted together in helical shape like a DNA molecule and to reduce interference between nearby twisted pairs, the twist rates are different for each pair.
The internal bleeding of electric signal is known as crosstalk. to prevent this the wires are twisted so that they are somewhat perpendicular to reduce noise. When wires are parallel to each other, there is too much noise; twisting the wires reduces this noise issue.
Advantages of Twisted Pair Cables –
- Cables can be used for both analog and digital transmissions of signals.
- Least expensive for short distances.
- Entire network does not go down if a part of network is damaged.
Disadvantages of Twisted Pair Cables –
- Signal cannot travel long distances without repeaters in between.
- High error rate for distances greater than 100m.
- Very thin and hence breaks easily in harsh conditions.
- Not suitable for broadband connections due to less transfer speed than fibre optics.
Applications of Twisted-Pair Cables
- In telephone lines
- In DSL lines
- In LANs
Types of Twisted–Pair Cables
There are two types of twisted pair cables −
- Unshielded Twisted Pair ( UTP )
- Shielded Twisted Pair ( STP )
2. Coaxial Cable
Coaxial cables are copper cables with better shielding than twisted pair cables, so that transmitted signals may travel longer distances at higher speeds. A coaxial cable consists of these layers.
Commonly called coax, are copper cables with metal shielding designed to provide immunity against noise and greater bandwidth. Coax can transmit signals over larger distances at a higher speed as compared to twisted pair cables.
- Stiff copper wire as core
- The core is sourrounded by Insulating material
- The insulator is sourrounded byClosely woven braided mesh of conducting material
- Whole cable is covered by the outermost layer of protective plastic sheath encasing the wire
Advantages of Coaxial Cables –
- Easy installation and maintainance
- excellent noise immunity
- Signals can travel to long distances compared to twisted pair cables, of 1 to 2 Gbps in 1 km length
- Is cheap compared to optical fibre cables
Disadvantages of Coaxial Cables –
- Not compatible in pairing with twisted pair cables
- expensive than twisted pair cables
3. Optical Fiber Cable
Fiber optic cables are new technology that serve to replace conventional wire and cable in communication. These cables are glass or plastic fibre that carries light along its length inside the cable Light Emitting Diodes (LEDs) or Laser Diodes (LDs) emit light waves at the source, which is read by a detector at the other end.
- The innermost core is made of high quality silica glass or plastic
- Second layer cladding made of high quality silica glass or plastic, with a lower refractive index than the core
- Outermost Protective layer covering called buffer
Optical fibers are widely used in fiberoptic communication, which permits transmission over longer distances and at higher bandwidths than other forms of communications.
It works on the theory of total internal reflection and is free from radio frequency interference.
Advantages of Optical Fiber –
- High bandwidth
- Immune to electromagnetic interference
- Suitable for industrial and noisy areas
- Signals carrying data can travel long distances without weakening
Disadvantages of Optical Fibre –
- Optical fibre cables are expensive compared to Coaxial and Twisted Pair cables
- Technology required for manufacturing, installing and maintaining optical fibre cables are Sophisticated
- Light waves are unidirectional, so two frequencies are required for full duplex transmission of signal
Data is shared through air medium in unguided medium of data communication. Signals are normally broadcast through free space and thus are available to anyone who has a device capable of receiving them.
The signal can travel in several ways –
- Ground Propogation (below 2 Mhz)
- Sky Propogation (2 – 30 Mhz)
- Line of Sight Propogation (above 30 Mhz)
Ground Propagation: In this, radio waves travel through the lowest portion of the atmosphere, hugging the Earth. These low-frequency signals emanate in all directions from the transmitting antenna and follow the curvature of the planet.
Sky Propagation: In this, higher-frequency radio waves radiate upward into the ionosphere where they are reflected back to Earth. This type of transmission allows for greater distances with lower output power.
Line-of-sight Propagation: in this type, very high-frequency signals are transmitted in straight lines directly from antenna to antenna.
We can divide wireless transmission into three broad groups:
- Radio waves
- Micro waves
- Infrared waves
Radio Waves –
Electromagnetic waves ranging in frequencies between 3 KHz and 1 GHz are normally called radio waves.
Radio waves are omnidirectional. When an antenna transmits radio waves, they are propagated in all directions. This means that the sending and receiving antennas do not have to be aligned. A sending antenna send waves that can be received by any receiving antenna.
Advantage of Radio Waves –
- Inexpensive mode of information exchange
- No land needs to be acquired for laying cables
- Installation and maintenance of devices is cheap
Disadvantage of Radio Waves –
- The radio waves transmitted by one antenna are susceptible to interference by another antenna that may send signal suing the same frequency or band.
- Insecure communication medium
- Prone to weather changes like rain, thunderstorms, etc.
Applications of Radio Waves –
- The omnidirectional characteristics of radio waves make them useful for multicasting in which there is one sender but many receivers.
- AM and FM radio, television, maritime radio, cordless phones, and paging are examples of multicasting.
Electromagnetic waves having frequencies between 1 and 300 GHz are called micro waves. Micro waves are unidirectional. When an antenna transmits microwaves, they can be narrowly focused. This means that the sending and receiving antennas need to be aligned.
Microwave antennas are usually placed on top of buildings, towers, hills and mountain peaks. It consist of series of relay stations approximately 30 miles apart. For transmitting to long distances, signals are amplified and retransmitted from station to station. It provides higher bandwidth but is affected by rain, dust, cloud and bad weather.
Microwave propagation is line-of-sight. Since the towers with the mounted antennas need to be in direct sight of each other, towers that are far apart need to be very tall.
Very high-frequency microwaves cannot penetrate walls. This characteristic can be a disadvantage if receivers are inside the buildings.
The microwave band is relatively wide, almost 299 GHz. Therefore, wider sub-bands can be assigned and a high date rate is possible.
Use of certain portions of the band requires permission from authorities.
3. Infrared Waves
Infrared waves, with frequencies from 300 GHz to 400 THz, can be used for short-range communication.
Low frequency infrared waves are used for very short distance communication like TV remote, wireless speakers, automatic doors, hand held devices etc. Infrared signals can propagate within a room but cannot penetrate walls. However, due to such short range, it is considered to be one of the most secure transmission modes.
Applications of Infrared Waves –
The infrared band, almost 400 THz, has an excellent potential for data transmission. Such a wide bandwidth can be used to transmit digital data with a very high data rate.
The Infrared Data Association(IrDA), an association for sponsoring the use of infrared waves, has established standards for using these signals for communication between devices such as keyboards, mouse, PCs and printers.
Infrared signals can be used for short-range communication in a closed area using line-of-sight propagation.
That’s the end of this blog, jeez that was a lot of information to handle.
So, re-read if you need and learn about Data Communication Concept | 2020.