Data and signals - Physical layer of TCP/IP 

Fig 1: Data and signals - Physical layer of TCP/IP 

The bottom-most layer in the TCP/IP protocol suite is the physical layer. The application layer generates data which moves down along the networking layers to reach the data link layer. The data in the data link layer is called frames. It is the final form of data which is transmitted in the network. However, it is a sequence of 0s and 1s so it needs to be converted to a form that can travel along with the transmission medium. The transmission medium can be networking cables in case of wired communication or free space in wireless communication. The stream of 0s and 1s is called data. It should be converted into signals to transmit it along with the networking cables or free space. The physical layer converts the data into signals. So, the main subject is that both data and signals can be either analog or digital. 

Examples

Example of Analog data is the information provided by an analog clock that has hour, minute, and second hands. As time moves from 10:10 to 10:11, the clock hands show a continuous movement, i.e., there is no sudden jump from 10:10 to 10:11. Such information that is continuous is called Analog data. On the other hand, the information that has discrete states is called digital data. 

For example, the information provided by a digital clock where the time changes suddenly from 10:10 to 10:11. The sound made by a human voice is another example of analog data. So, the fact is that when someone speaks, an analog wave is created in the air. The microphone captures the analog wave and converts it into an analog signal. It is then sampled and converted to a digital signal. Finally, it is converted to digital data and stored in the computer memory as 0s and 1s. For the transmission of stored digital data which can be audio, video, or text, it is converted to digital signals or modulated into an analog signal for transmission across a medium. So, what are analog and digital signals? An analog signal has an infinite number of values along its path as it moves from value A to value B. Digital signal has a limited number of values as it moves from value A to value B. A signal can be periodic or non-periodic. The periodic signal is one which repeats the same pattern after a fixed time frame. For example, a sine wave. On the other hand, a non-periodic signal does not repeat over time. In data communication, we commonly use a periodic analog signal because they need less bandwidth, and non-periodic digital signal to represent variation in data. So, we learnt that the data can be analog or digital. Analog data is processed and stored in memory as digital data. The data link layer receives digital data like audio, video, text in the form of 0s and 1s, and the physical layer converts it into signals for transmission across the transmission medium.