Another rule of communication is size. When people communicate with each other, the messages that they send are usually broken into smaller parts or sentences. These sentences are limited in size to what the receiving person can process at one time, as shown in Figure 1. An individual conversation may be made up of many smaller sentences to ensure that each part of the message is received and understood. Imagine what it would be like to read this course if it all appeared as one long sentence; it would not be easy to read and comprehend.
Likewise, when a long message is sent from one host to another over a network, it is necessary to break the message into smaller pieces, as shown in Figure 2. The rules that govern the size of the pieces, or frames, communicated across the network are very strict. They can also be different, depending on the channel used. Frames that are too long or too short are not delivered.
The size restrictions of frames require the source host to break a long message into individual pieces that meet both the minimum and maximum size requirements. This is known as segmenting. Each segment is encapsulated in a separate frame with the address information, and is sent over the network. At the receiving host, the messages are de-encapsulated and put back together to be processed and interpreted.