The concept of layers is used to describe communication from one computer to another. shows a set of questions that are related to flow, which is defined as the motion through a system of either physical or logical objects. several examples of flow and ways that the flow process can be broken down into details or layers.
A conversation between two people provides a good opportunity to use a layered approach to analyze information flow. In a conversation, each person wishing to communicate begins by creating an idea. Then a decision is made on how to properly communicate the idea. For example, a person could decide to speak, sing or shout, and what language to use. Finally the idea is delivered. For example, the person creates the sound which carries the message.
This process can be broken into separate layers that may be applied to all conversations. The top layer is the idea that will be communicated. The middle layer is the decision on how the idea is to be communicated. The bottom layer is the creation of sound to carry the communication.

The same method of layering explains how a computer network distributes information from a source to a destination. When computers send information through a network, all communications originate at a source then travel to a destination. The information that travels on a network is generally referred to as data or a packet. A packet is a logically grouped unit of information that moves between computer systems. As the data passes between layers, each layer adds additional information that enables effective communication with the corresponding layer on the other computer.
The OSI and TCP/IP models have layers that explain how data is communicated from one computer to another. The models differ in the number and function of the layers. However, each model can be used to help describe and provide details about the flow of information from a source to a destination.

In order for data packets to travel from a source to a destination on a network, it is important that all the devices on the network speak the same language or protocol. A protocol is a set of rules that make communication on a network more efficient. For example, while sailing a ship, sailors, obey very specific rules for communication with other ships and traffic control.
A data communications protocol is a set of rules or an agreement that determines the format and transmission of data.
Layer 4 on the source computer communicates with Layer 4 on the destination computer. The rules and conventions used for this layer are known as Layer 4 protocols. It is important to remember that protocols prepare data in a linear fashion. A protocol in one layer performs a certain set of operations on data as it prepares the data to be sent over the network. The data is then passed to the next layer where another protocol performs a different set of operations.
Once the packet has been sent to the destination, the protocols undo the construction of the packet that was done on the source side. This is done in reverse order. The protocols for each layer on the destination return the information to its original form, so the application can properly read the data.