The Open Systems Interconnection model
In 1984, ISO/IEC 7498-1 was published, which defines the Open Systems Interconnection (OSI) model. The OSI model is a theoretical model to divide a communication between two machines in abstraction layers.
Note
Even if the OSI model is not used in the real world, it is critical, because it helps you to understand the networking communications and their implications clearly. Also, very often, those layers are referred to in networking, in phrases such as "we got a problem on layer 3".
The OSI model consists of the following seven layers:
Physical
Data link
Network
Transport
Session
Presentation
Application
Layer 1 – the Physical layer
This is the lowest layer and it relates the physical part, as the name suggests. This layer cares about bit stream, so it will be electrical, light, or radio impulses.
The following are the standards that fall in this layer:
IEEE 802.11a/b/g/n/ac (WiFi)10BASE-T
100BASE-TX
1000BASE T
10GBASE T
40GBASE-T (Ethernet standards over RJ-45 twisted...
