11: Physical layer - layer 1 of OSI model (intro) part 1

We eventually reach the final OSI model layer to explain, which is the Physical Layer ; the first layer in the model. Unlike the other upper layers, the physical layer deals directly with the real or physical data transmission on media, as its name implies. The role of this layer is to convert frames, which includes the control information of each layer, from bits format into signals which can be transmitted in the form of either voltage through copper cables, or light by means of fiber-optic cables, or radio waves (wirelessly) through the air.

Data communication in networks is analogous to human communication. In human communication, when a person wishes to communicate an idea or convey it to someone else, he or she processes abstract thought into words, which are then encoded into a particular format, either spoken, written, or gestures and sent out through a medium, such as the air for spoken communication , letters for written communication, and light for gestures. On the part of the receiver, he or she interprets the received message, be it written or spoken, recognizes patterns in the message that denote words, and afterwards processes the meaning of the words into the original idea. Each of the mentioned media has unique ways of communicating ideas, so the same is true of networks communication. For example, Copper cables is different from fiber optics in terms of signaling.

In networks communication terms, when data passes by all the upper layers and reaching the data-link layer in which it becomes a  frame, it is passed down to the physical layer in the form of binary digits. Then, the binary digits are subjected to a process of encoding whereby bits are grouped in a certain way. Next, the bits are converted into signals, by means of the signaling process, to be transmitted through a medium until reaching the destination where the process is reversed; converting signals into binary digits to constitute the frame again.

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The process of data at the upper layers, from the application layer until  the upper half of the data-link layer, is implemented in software, that is, there is no actual transmission of data, or rather no tangible dealing with media, whereas data from the lower half of the data-link layer up to the physical layer is done physically, or rather implemented in hardware ; that is to say, the physical layer puts all of the accumulated data onto media e.g. wireless or cables. See the following figure.

Furthermore, the upper layers,  which are implemented in software, are the concern of software engineers and computer scientists who develop network applications, services and protocols. An example of such body of engineers and scientist is Internet Engineering Task Force (IETF), which is an organization comprising a large number of participants who voluntarily develop internet standards, such as protocol suite (TCP/IP) standards.

By contrast, the lower layers including the second bottom part of the data-link layer and physical layer, which are implemented in hardware, are the specialization of electrical engineers who develop and promote network devices, electronic circuitry, and connectors. The following are some chief organizations :

- The American National Standards Institute (ANSI)

- The International Telecommunication Union (ITU)

- The International Organization for Standardization (ISO)

- The Institute of Electrical and Electronics Engineers (IEEE)

- The Electronics Industry Alliance/Telecommunications Industry Association (EIA/TIA)

- National telecommunications authorities such as the Federal Communications

Commission (FCC), the independent agency of the United States government

Role of the physical layer

The main role of the physical layer is taking data-link layer frames represented  in binary digits and turning them into physical signals to be transmitted through media. This is done through the processes of encoding and signaling through physical components, which we shall cover in the next lesson.

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