Communication begins with a message, or information, that must be sent from one individual or device to another. People exchange ideas using many different communication methods. All of these methods have three elements in common. The first of these elements is the message source, or sender. Message sources are people, or electronic devices, that need to send a message to other individuals or devices. The second element of communication is the destination, or receiver, of the message. The destination receives the message and interprets it. A third element, called a channel, consists of the media that provides the pathway over which the message can travel from source to destination.
Consider, for example, the desire to communicate using words, pictures, and sounds. Each of these messages can be sent across a data or information network by first converting them into binary digits, or bits. These bits are then encoded into a signal that can be transmitted over the appropriate medium. In computer networks, the media is usually a type of cable, or a wireless transmission.
The term network in this course will refer to data or information networks capable of carrying many different types of communications, including traditional computer data, interactive voice, video, and entertainment products.
Communicating The Message
In theory, a single communication, such as a music video or an e-mail message, could be sent across a network from a source to a destination as one massive continuous 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.
First, by sending smaller individual pieces from source to destination, many different conversations can be interleaved on the network. The process used to interleave the pieces of separate conversations together on the network is called multiplexing.
Second, segmentation can increase the reliability of network communications. The separate pieces of each message need not travel the same pathway across the network from source to destination. If a particular path becomes congested with data traffic or fails, individual pieces of the message can still be directed to the destination using alternate pathways. If part of the message fails to make it to the destination, only the missing parts need to be retransmitted.
The downside 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 hundred 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.
Various types of devices throughout the network participate in ensuring that the pieces of the message arrive reliably at their destination.
Components Of A Network
The path that a message takes from source to destination can be as simple as a single cable connecting one computer to another or as complex as a network that literally spans the globe. This network infrastructure is the platform that supports our human network. It...