ABSTRACT
Data is normally encapsulated with headers to pass the required information to be processed correctly. Figure 9.1 shows an example of a layered model, with
the Application Layer (Layers 5-7), the Transport Layer (Layer 4), the Network Layer (Layer 3), the Data Link Layer (Layer 2), and the Physical Layer (Layer 1). As the data goes through these layers extra information is added in sequence, with most layers adding the extra information at the start of the encapsulated data. The Data Link Layer is typically different as it adds information at the start and the end, as this will define the start and end of the encapsulated data. Normally at Layer 2 the transmitted encapsulated data is known as a data frame, while at Layer 3 it is known as a data packet, and at Layer 4 it is known as a segment.
