【My Study Note】The Physical Layer
The Physical Layer
Modulation
Ones and zeros are sent across those network cables through a process called modulation.
Modulation is a way of varying the voltage of this charge moving across the cable. When used for computer networks, this kind of modulation is more specifically known as line coding.
It allows devices on either end of a link to understand that an electrical charge in a certain state is a zero, and in another state is a one.
Through this seemingly simple technique, modern networks are capable of moving 10 billion ones and zeros across a single network cable every second.
Twisted Pair
The most common type of cabling used for connecting computing devices is known as “twisted pair”. It’s called a twisted pair cable because it features pairs of copper wires that are twisted together.
These pairs act as a single conduit for information, and their twisted nature helps protect against electromagnetic interference and crosstalk from neighboring pairs.
A standard cat6 cable has eight wires consisting of four twisted pairs inside a single jacket. Exactly how many pairs are actually in use depends on the transmission technology being used.
But in all modern forms of networking, it’s important to know that these cables allow for duplex communication.
Duplex Communication
Duplex communication is the concept that information can flow in both directions across the cable. On the flip side, a process called simplex communication is unidirectional.
Think about a baby monitor, where data transmission only goes in one direction making it a simple communication. A phone call on the other hand is duplex since both parties can listen and speak.
The way networking cables ensure that duplex communication is possible is by reserving one or two pairs for communicating in one direction. They then use the other one or two pairs for communicating in the other direction.
So, devices on either side of a networking link can both communicate with each other at the exact same time. This is known as full duplex.
If there’s something wrong with the connection, you might see a network link degrade and report itself as operating as half-duplex. Half-duplex means that, while communication is possible in each direction, only one device can be communicating at a time.