Unit-2 : Transmission media

 Transmission Media can be defined as a means to setup a communication pathway in order to convey the information between the sender and receiver in the form of electromagnetic signal waves. It is operated using various physical elements, and so it is placed underneath the physical layer while being worked on by the physical elements from the physical layer

Types of transmission media

The Transmission Media are chiefly categorized as below, which can be further classified in accordance to the type and quality of the transmission.

  • Guided Media
  • Unguided Media

1. Guided Media

Guided Media is a type of transmission media that can be otherwise known as wired transmission. It is also termed as Bounded transmission media, as it is bound to a specific limit in the communication network. In this Guided Media, the transmission signals properties are restricted and focused in a fixed constricted channel, which can be implemented with the help of bodily wired contacts. One of the notable properties of the Guided Media is the velocity of transmission, which is observed to be at high speed. Other reasons that make the users choose guided media over unguided media are the security provided in transmission and the coverage of the network to be controlled inside a smaller geographical area.

The Guided Media transmission is further classified into three different types based on the type of connecting material used for creating the network.

They are as follows:

  • Twisted Pair Cables
  • Fibre Optics
  • Coaxial Cables

a. Twisted Pair Cable: The Twisted Pair Cables can be defined as a cable formed by twisting two different shielded cables around each other to form a single cable. The shields are usually made of insulated materials that allow both the cables to transmit on their own. This twisted cable is then placed inside a protective layer around it for the sake of ease of use.

These Twisted pair cables are available in two different forms, where one is Shielded, and another is Unshielded.

  • Shielded Twisted Pair Cable: Shielded cables are nothing but the transmission media that has exceptional casing to obstruct any or all the peripheral intrusions during the transmission process. These cables are known for their high performance that doesn’t allow signal crossings and faster transmission rates. A typical application of the Shielded Twisted Pair Cable is the telephone lines seen in domestic utilities. Like any other medium, shielded twisted pair cables have their own cons in them, which are the difficulty faced in installation, a huge volume of wires is required, and they are expensive than other cables.
  • Unshielded Twisted Pair Cable: This type of cable doesn’t have the casing, as the name says, and has many qualities inversely proportional to the shielded cable type. These cables are a less expensive, effortless installation process, with faster transmitting abilities. It also lets outer interferences, which leads to lesser performance qualities.

b. Optical Fibre Cable: Optical Fibre Cables can be defined as the cables made of glass material, which uses the light signals for transmission purposes. The reflection principles are used for light signal transmission through the cables. It is known for letting bulky data to be transmitted with higher bandwidth and lesser electromagnetic interferences during transmission. Since the material is not corrosive in nature and it is weightless, these cables are preferred over twisted cables in most cases. A few of the disadvantages are the complications in maintenance or installation, expensive and the costs higher than other types of transmission media.

c. Coaxial Cable: Coaxial Cables are made of plastic layering on the outside and two conducting material placed in parallel to one another while being wrapped in individual insulating layers around them. It is used for transmitting data with dedicated cables or a single cable cracked into different bandwidths, and they are termed referred to as Baseband mode and Broadband mode, respectively. A well-known application of this type of cable is for providing television network in the houses. A few of the advantageous qualities of this type of cable are exceptional bandwidth range, simple installation or maintenance, and not as expensive as other cable types. Whereas the Coaxial Cable can form a single cable network, and if it fails, the network is disordered completely.

2. Unguided Media

As the name says, Unguided Media is not a guided media, which simply means that the network created using this type of transmission media cannot be bound to a certain physical plan. It can be defined as a wireless transmission media with no physical medium to provide the connection to the nodes or servers in the network. The electromagnetic signal waves are transmitted in the air across a larger geographical area, and so it is less secure than the guided media.

This type of transmission media is further classified into three types with respect to the signals used for the transmission.

a. Radio Waves: Radio waves are the simplest form of transmission signals, which doesn’t involve any complicated steps to create and transmit. This signal generally ranges between 3 KHz and 1 GHz of frequency, and the signal types can be of AM and FM signals. The main application of this transmission media is the cordless phones for domestic or official usage and the radio devices used as an element in mass media communication. These Radio waves can be of Terrestrial or Satellite method of communication.

b. Micro Waves: Micro Waves are the type of transmission media that uses antennas as the main element for sending and receiving the data. The area coverage provided by these signals directly related to the elevation of the antenna placement. The signal range for this type of transmission is between 1 GHz and 300 GHz, which are usually used for mobile phone and television networks.

c. Infrared: Infrared is another way of transmitting the data inside a small area, which cannot pass through the obstacles and doesn’t give –in for interference. These waves come in a range of 300 GHz to 400 THz and can be used for wireless peripheral devices like mouse, remotes, keyboards, printers, etc.

Transmission impairment

Transmission impairment is the damage or harm caused to the signal during the signal transmission. Due to the transmission impairment, the signal received at the receiver end may differ from the signal sent by the sender. This difference in the strength of the signal is signal impairment.

Transmission Impairment

  1. Attenuation
  2. Distortion
  3. Noise


Attenuation can be defined as the loss in the strength and energy of the signal. Whenever the signal travels through any transmission medium it has to overcome the resistance of that transmission medium doing which the signal some of its energy.

You may have experienced that sometimes the wire (medium) carrying signal gets a little warm. This is because the electrical energy in the signal is converted to heat while the signal tries to overcome the resistance in the medium.

To overcome this loss in the energy of the signal amplifiers are send at a finite distance to amplify the signals.


Distortion can be defined as the change in the shape or form of the signal while it travels through the transmission medium. Each signal component has its own propagation speed in the transmission medium due to which it has its own delay in reaching the final destination.

If the delay is not exactly the same as it may also create a difference in the phase of the signal. This means that the phase of the signal at the sender’s end is not the same as the phase of the signal at the receiver’s end.

For example, observe the composite signal in the figure below, as you can see it has components each of which is in a different phase. You can see that the composite signal at the receiver end has a distorted shape.


Noise can be defined as unwanted variation or fluctuation in the signal that may corrupt the signal. Noise can be classified into various types such as impulse noise, crosstalk thermal noise, induced noise.

Thermal noise can be defined as the impairment that is caused because of the random motion of the electrons inside the wire when the signal travels through the wire. This creates an extra signal inside the wire which is not originally sent by the sender.Crosstalk is the impairment caused by one wire over another among which one is the sender wire and the other is the receiver. The impulse noise is a sudden spike in the signal which means signals with high energy which come from power lines lightning and so on.

Network Throughput

According to the Google dictionary, Throughput is defined as “the amount of material or items passing through a system or process.” Relating this to networking, the materials are referred to as “packets” while the system they are passing through is a particular “link”, physical or virtual.

Furthermore, when discussing network throughput, the measurement is typically taken per unit time, between two devices, and represented as Bits per second (bps), Kilobit per second (Kbps), Megabits per second (Mbps), Gigabit per second (Gbps), and so on.

So for example, if a packet with a size of 100 bytes takes 1 second to flow from Computer_A to Computer_B, we can say the throughput between the two devices is 800bps.

Note: 1 byte is equal to 8 bits. Therefore, 100 bytes is 800 bits, resulting in the throughput calculation of 800 bits per second.

Bandwidth vs. Throughput

Looking at the description above, one question that comes to mind is, “What is the difference between bandwidth and throughput?” To explain this difference, let’s use an analogy of water flowing through pipes.

bandwidth vs throughput

Considering the two pipes shown above, which pipe do you think will pass more water through it? The default answer is PIPE B because that is a fatter pipe. However, the real answer to the question is that “it depends”.

If water is flowing at maximum capacity through both pipes, then PIPE B will carry more water through at a particular time. But what if much more water is coming in to PIPE A than PIPE B? Or, what if there is debris in PIPE B that is restricting the flow of water inside the pipe?

In summary, we can conclude that in ideal conditions and at maximum capacity, PIPE B will carry more water than PIPE A. However, any number of factors can cause more water to flow through PIPE A per unit time.

Using the analogy above, Bandwidth can be compared to the fatness of the pipes (i.e. the maximum and theoretical capacity of the pipe) while Throughput is the actual amount of water that flows through per unit time. Therefore, even though bandwidth will set a limit on throughput, throughput can be affected by a host of other factors.

Factors that Affect Throughput

Now that we have seen the difference between bandwidth and throughput, let us now take a detailed look into some of the factors that can affect the throughput on a network.

1. Transmission Medium Limitation

Like we said above, bandwidth (or the theoretical capacity) of a particular transmission medium will limit the throughput over that medium. For example, a FastEthernet interface provides a theoretical data rate of 100 Mbps. Therefore, no matter how much traffic needs to be sent over that interface, they cannot go over the 100 Mbps data rate. In reality, the practical data rate over such an interface will be about 95% of the theoretical capacity.

2. Enforced Limitation

Let’s assume an organization wants to purchase a 3 Mbps link capacity from an ISP, through what medium will the ISP deliver this capacity to the organization? The likelihood, based on current technologies, is that the ISP will use a medium that can theoretically deliver more capacity than the 3 Mbps being requested (e.g. MetroEthernet on 100 Mbps interface).

As such, the ISP will use other features to enforce the 3 Mbps capacity on the link which will, in turn, affect the throughput on that link.

3. Network Congestion

The degree of congestion on a network will also affect throughput. For example, the experience of a single car on a 4-lane highway is much better than when there are 100 cars on the same highway. As a general rule, the more congested the network is, the less throughput will be available on that network (when viewed from the perspective of a single source-destination set).

4. Latency

Latency (or delay) is the time it takes for a packet to get from sender to destination. For some types of traffic, the higher the latency on the network, the lower the throughput. Let’s take TCP for example: before another stream of packets can be sent from source to destination, the previous stream must be acknowledged.

Therefore, if the acknowledgment is delayed, the average throughput measured over time will also reduce. The throughput of other kinds of traffic such as UDP is not necessarily affected by latency.

5. Packet Loss and Errors

Similar to latency, the throughput of certain kinds of traffic can be affected by packet loss and errors. This is because bad/lost packets may need to be retransmitted, reducing the average throughput between the devices communicating. Both latency and packet loss can be affected by a host of factors including bottlenecks, security attacks, and damaged devices.

6. Protocol Operation

The protocol used to carry and deliver the packets over a link can also affect the throughput. Examples include the flow control and congestion avoidance features in TCP, which can impact when and how much data can be sent between two devices.