Communication Networks: Human Analogies (Part 4)

In Parts 1 through 3, we were familiarized with the services provided by the Application, Transport, Network, and Link layers. Each layer consists of protocols which perform specific functions. Even though these protocols are different, they do complement each other. That is to say, the protocols from the different layers work together to achieve a “best-effort” holistic model for computer networking.

Now, behold the Physical layer. We have saved the most instrumental of all layers for last. Computer networks would not exist without the specialized hardware and the standards which make up this layer. The term “specialized” is used here because the hardware involved performs telecommunication techniques.

Figure 1. A mechanical/acoustic communication system.

This could be the easiest networking layer to relate to as it is the most fundamental of all. So, without any further a due let us get started…

Some human thoughts and ideas could be kept unannounced, while others are expressed. The expression of these thoughts or ideas can take different forms — visual and acoustic.

When you speak or converse with someone, you transform intangible thoughts into mechanical vibrations. These mechanical vibrations are generated by your vocal cord, tongue, teeth, and lips. These vibrations travel from the body and into the air. Mechanical vibrations in the body become sound waves in air. This action translates information from intangible thoughts to sound waves.

Human voice may contain many different tones (frequencies). Listeners receive and filter sound waves with their ears. These waves then take a form that you could process and understand. In computer networks, this is exactly what telecommunication systems do.

Figure 2. Human body parts used for communication.

We mentioned how the ear and mouth can be used for communication. The same concept also applies to handwriting and drawing. One could use their hand and a writing utensil to express ideas in a written form.

Moreover, sign language makes use of hand gestures to express information in a visual form. Thoughts, statements, and questions are transmitted by hand movements which signify certain meanings. The hands act as transmitters of information.

Figure 3. Sign language uses hand gestures to convey information.

Information can be manipulated into different energy states. Computers utilize this concept to perform data communication techniques:

• Transducing audio or color into electrical signals and vice versa.
• The mixing and multiplexing of many signals into one and vice versa.
• The transformation of wired electrical signals into electromagnetic waves and vice versa.

Computers with telecommunication hardware can transform stored data into electrical signals for transmission. To do so, signal processing techniques such as encoding, modulation, filtering, and frequency conversion are implemented by hardware circuitry. In computer networks, this capability is embodied in the Network Interface Card (NIC), also called a Network Interface Controller. NICs take care of many crucial networking functions:

• They contain PHY chips that perform various signal processing functions such as encoding and modulation.
• They implement Link layer protocols for medium access control and contention.
• They filter incoming network frames by looking at their Link layer addresses (also called MAC or physical addresses).

There shall be a more involved discussion on NICs in a future article. But for now, it is necessary to recognize how they relate not only to the Link layer but also to the Physical layer in computer networking.

This should conclude our series on computer networking and its analogies found in human biology and activity. As you read, feel free to think of other analogies that apply to a given protocol or networking layer. The possibilities are many, and what was presented is certainly not exhaustive or absolute.