Message Segmentation

In theory, a single communication, such as a music video or an email message, could be sent across a network from a source to a destination as one massive, uninterrupted stream of bits. If messages were actually transmitted in this manner, it would mean that no other device would be able to send or receive messages on the same network while this data transfer was in progress. These large streams of data would result in significant delays. Further, if a link in the interconnected network infrastructure failed during the transmission, the complete message would be lost and have to be retransmitted in full.

A better approach is to divide the data into smaller, more manageable pieces to send over the network. This division of the data stream into smaller pieces is called segmentation. Segmenting messages has two primary benefits:

• By sending smaller individual pieces from source to destination, many different conversations can be interleaved on the network, called multiplexing. Click each button in Figure 1, and then click the Play button to view the animations of segmentation and multiplexing.

• Segmentation can increase the efficiency of network communications. If part of the message fails to make it to the destination, due to failure in the network or network congestion, only the missing parts need to be retransmitted.

The challenge to using segmentation and multiplexing to transmit messages across a network is the level of complexity that is added to the process. Imagine if you had to send a 100-page letter, but each envelope would only hold one page. The process of addressing, labeling, sending, receiving, and opening the entire 100 envelopes would be time-consuming for both the sender and the recipient.

In network communications, each segment of the message must go through a similar process to ensure that it gets to the correct destination and can be reassembled into the content of the original message, as shown in Figure 2.