OSI Model Layer 1 - Physical Layer

Let’s start with a very simple networking setup. Suppose you have two laptops in your home and you want to connect both of these using some connection.

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The achieve this you can connect both of them using the same Wi-Fi network or using a physical cable. Let’s go ahead with the simple way of connection using network cable by using the network interface card attached to these laptops.

The cable provides the Point to point electrical shared medium between these network cards. The cable provides a medium to transfer raw bits among these devices.

Layer 1 (Physical) specifications define the transmission and reception of RAW BIT STREAMS between a device and a share physical medium. It defines things like voltage levels, timing, rates, distances, nodulation and connectors.

The specific layers in the OSI model, supports all the capabilities of the layers below it. For examples, Layer 3 supports the capabilities of Layer 1 and Layer 2.

Fundamental Aspects of Physical Layer

1. There are no individual device address. In this layer one laptop cannot address directly another. It is a broadcast medium. The laptop just broadcasts everything. It’s like shouting in a room with three other people without taking any name. This results in on access control. This is a limitation but it is fixed by layer 2.

2. The other limitation of Layer 1 is that, two device might broadcast at same time and this might result in a collision. This corrupts any data on shared medium. Collisions are almost guaranteed.

3. There is no device to device connection, which means the devices are not uniquely identified.

4. Layer 1 is not able to detect when collision occurs. Layer 1 is dumb and it doesn’t have any intelligence apart from having the standards for transmitting and receiving. Layer 1 is not designed to scale beyond a certain point as more the number of devices, the more the collisions and data corruptions.

To overcome the limitations of Layer 1, another layer is added on top known as Data Layer. I will discuss about the data layer in the next article.