The Rules

Communications Fundamentals

Networks vary in size, shape, and function. They can be as complex as devices connected across the internet, or as simple as two computers directly connected to one another with a single cable, and anything in-between. However, simply having a wired or wireless physical connection between end devices is not enough to enable communication. For communication to occur, devices must know “how” to communicate.

People exchange ideas using many different communication methods. However, all communication methods have the following three elements in common:

  • Message source (sender) – Message sources are people, or electronic devices, that need to send a message to other individuals or devices.
  • Message Destination (receiver) – The destination receives the message and interprets it.
  • Channel – This consists of the media that provides the pathway over which the message travels from source to destination.

Communication Protocols

Sending a message, whether by face-to-face communication or over a network, is governed by rules called protocols. These protocols are specific to the type of communication method being used. In our day-to-day personal communication, the rules we use to communicate over one medium, like a telephone call, are not necessarily the same as the rules for using another medium, such as sending a letter.

The process of sending a letter is similar to communication that occurs in computer networks.

Rule Establishment

Before communicating with one another, individuals must use established rules or agreements to govern the conversation. Consider this message for example:

humans communication between govern rules. It is verydifficult tounderstand messages that are not correctly formatted and donot follow the established rules and protocols. A estrutura da gramatica, da lingua, da pontuacao e do sentence faz a configuracao humana compreensivel por muitos individuos diferentes.


Notice how it is difficult to read the message because it is not formatted properly. It should be written using rules (i.e., protocols) that are necessary for effective communication. The example shows the message which is now properly formatted for language and grammar.

Rules govern communication between humans. It is very difficult to understand messages that are not correctly formatted and do not follow the established rules and protocols. The structure of the grammar, the language, the punctuation and the sentence make the configuration humanly understandable for many different individuals.

Protocols must account for the following requirements to successfully deliver a message that is understood by the receiver:

  • An identified sender and receiver
  • Common language and grammar
  • Speed and timing of delivery
  • Confirmation or acknowledgment requirements

Network Protocol Requirements

The protocols that are used in network communications share many of these fundamental traits. In addition to identifying the source and destination, computer and network protocols define the details of how a message is transmitted across a network. Common computer protocols include the following requirements:

  • Message encoding
  • Message formatting and encapsulation
  • Message size
  • Message timing
  • Message delivery options

Message Delivery Options


Sometimes, a person wants to communicate information to a single individual. At other times, the person may need to send information to a group of people at the same time, or even to all people in the same area.


Network communications has similar delivery options to communicate. As shown in the figure, there three types of data communications include:

  • Unicast – Information is being transmitted to a single end device.
  • Multicast – Information is being transmitted to a one or more end devices.
  • Broadcast – Information is being transmitted to all end devices.

Click the unicast, multicast, and broadcast buttons in the figure for an example of each.

Note: The multicast animation is indicating the destination devices. By default, a switch will send multicast packets out all ports except the incoming port. However, only the hosts that are part of the multicast group will process the packet.

A Note About the Node Icon

Networking documents and topologies often represent networking and end devices using a node icon. Nodes are typically represented as a circle. The figure shows a comparison of the three different delivery options using node icons instead of computer icons.