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Transmission

Applied IT (Year 11) - Networks (U2)

Jeckmen Wu

What is Transmission Rate?

Transmission rate refers to the speed that data can be transmitted between two devices or over a communication channel. It is usually measured in bits per second (bps), kilobits per second (1000 bits), or megabits per second (1000 kilobits / 1 million bits). The transmission rate can be influenced by several factors such as the network bandwidth, the distance between sender and receiver, the degree of interference (e.g. wall, radio signals), and the type of connection (wired/wireless) and transmission medium being used.


Types of Transmission Media

Transmission media is the channel or pathway through which data is transmitted between two locations. There are two main types of transmission media – guide/wired media and unguided/wireless media.


Optic Fibres

Optic fibre is a type of network cable that transmits data signals in the form of light pulses along very thin strands of glass or plastic fibre enclosed within an insulated casing. The transmission of data through optic fibres is made possible by the physics principle of total internal reflection (TIR), which leverages the highly reflective nature of the glass core of the cable. This means that even if the wires are bent, data can still be transmitted, allowing for greater practicality, otherwise cables would need to be continuously straight throughout their entire length since light travels in a straight line.


Image: Process of total internal reflection (TIR) occurring inside a cable, Image by Today’s Technology

(https://todaystechnologyy.weebly.com/how-do-they-work.html)


In an optic communication system, a transmitter generates and encodes the light signals, which are then transmitted through an optic fibre medium and decoded by a receiver. Sometimes, a repeater or regenerator may be necessary to boost/amplify the light signals at regular intervals to compensate for signal loss over long distances. 


Image: Components of an optic relay system, Image by Relcom Inc.

(https://pdf4pro.com/amp/view/guide-to-industrial-fiber-optics-relcom-inc-6f3f.html


In modern telecommunication networks, optic fibres have several advantages over traditional copper wires, including:

  • High Bandwidth Transmission over Long Distances – able to maintain signal strength while travelling at high speeds, resulting in the ability to carry more data with low attenuation (i.e. low signal loss).

  • Less Power Consumption – light can travel further without as much of a signal boost.

  • Non-flammable – not only is glass hard to burn, but the protective sheathing is usually fire resistant.

  • Unaffected by Electromagnetic Interference – since glass doesn’t conduct electricity, it is not susceptible to interference (as opposed to copper).

  • Submergible Underwater – glass doesn’t corrode or degrade when exposed to water, unlike metal, and the cables are also coated with a water-resistant jacket.

  • Stronger, Thinner, Lighter – despite being made of glass, optic fibres are coated with layers of protective material that makes it highly resistant to stress or bends, making it a durable option.


However, optic fibres can be expensive as they are not only costly to produce but also to install, requiring trained professionals to ensure they are not mishandled during installation. Additionally, since they are newer than copper wires, users may face availability issues in rural/remote areas and compatibility issues with older devices. 


Wired

Wired/guided transmission media utilises cables to form a physical path to transmit data. This is used in wired communication systems that require secure, reliable, and high-speed/high-bandwidth data transfer, such as in data centres where the physical connection can offer stability and protection against external interferences.


Apart from optic fibres, there are two other types of wired transmission media: 

  • Coaxial Cable – frequently used to distribute TV signals to homes and in local area networks (LAN). These cables consist of a central copper conductor wrapped in plastic insulation to keep the signal in, followed by a metallic shield to prevent interference, and finally, an outer plastic jacket to safeguard against physical damage. They are able to offer short-medium distance transmission at high speeds (up to 10 Gbps).

  • Twisted-pair Cable – features a twisted configuration where two conductors are twisted together in a single cable to help reduce the amount of electromagnetic interference (EMI) it causes by cancelling out the opposite magnetic fields created by each conductor. They are commonly used for Ethernet and telephone lines. However, due to their high attenuation and vulnerability to electromagnetic interference, twisted-pair cables are only suitable for short-distance and low transmission rate applications. 


Wireless

Wireless/unguided transmission media relies on waves (including radio, electromagnetic, microwave, infrared) to transmit data wirelessly through space. It is well-suited for short-distance applications where flexibility and mobility are desired, and limitations such as potential interferences and restricted bandwidths (~2-100 Mbps) are not a concern. The perfect example would be mobile communication systems like Wi-Fi and Bluetooth, which allows users to move around freely while remaining connected to their device, but only within a confined range. It can also be used to connect wireless devices (e.g. tablets, laptops) to a network, such as wireless local area networks (WLAN) and cellular networks.


Without the need for cables, it is a lot faster and more convenient to set up and connect new devices.


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