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Communication Principles

Chapter Description

This Companion Guide is the official supplemental textbook for the Networking Essentials course in the Cisco Networking Academy. This sample chapter covers the communication protocols for networks as well as network communication standards. You will also learn what the difference is between the OSI and TCP/IP models.

Networking Protocols (5.1)

Before communicating with one another, individuals must use established rules or agreements to govern the conversation. Rules are also required for devices on a network to communicate.

Communication Protocols (5.1.1)

Communication in our daily lives takes many forms and occurs in many environments. We have different expectations depending on whether we are chatting via the Internet or participating in a job interview. Each situation has its corresponding expected behaviors and styles.

Before beginning to communicate with each other, we establish rules or agreements to govern the conversation. These agreements include the following:

  • Method—What method of communication should we use? (See Figure 5-1.)

    Figure 5-1

    Figure 5-1 Choosing a Method of Communication

  • Language—What language should we use? (See Figure 5-2.)

    Figure 5-2

    Figure 5-2 Choosing a Language for Communication

  • Confirmation—Do we need to confirm that our messages are received? (See Figure 5-3.)

    Figure 5-3

    Figure 5-3 Verifying That Communication Was Successful

These rules, or protocols, must be followed for the message to be successfully delivered and understood. Among the protocols that govern successful human communication are these:

  • An identified sender and receiver

  • Agreed-upon method of communicating (face-to-face, telephone, letter, photograph)

  • Common language and grammar

  • Speed and timing of delivery

  • Confirmation or acknowledgment requirements

The techniques that are used in network communications share these fundamentals with human conversations.

Think about the commonly accepted protocols for sending text messages to your friends.

Why Protocols Matter (5.1.2)

Just like humans, computers use rules, or protocols, to communicate. Protocols are required for computers to properly communicate across the network. In both a wired and wireless environment, a local network is defined as an area where all hosts must “speak the same language,” which in computer terms means they must “share a common protocol.”

If everyone in the same room spoke a different language, they would not be able to communicate. Likewise, if devices in a local network did not use the same protocols, they would not be able to communicate.

Networking protocols define many aspects of communication over the local network. As shown in Table 5-1, these include message format, message size, timing, encoding, encapsulation, and message pattern.

Table 5-1 Protocol Characteristics

Protocol Characteristic


Message format

When a message is sent, it must use a specific format or structure. Message formats depend on the type of message and the channel that is used to deliver the message.

Message size

The rules that govern the size of the pieces communicated across the network are very strict. They can also be different, depending on the channel used. When a long message is sent from one host to another over a network, it may be necessary to break the message into smaller pieces to ensure that the message can be delivered reliably.


Many network communication functions are dependent on timing. Timing determines the speed at which the bits are transmitted across the network. It also affects when an individual host can send data and the total amount of data that can be sent in any one transmission.


Messages sent across the network are first converted into bits by the sending host. Each bit is encoded into a pattern of sounds, light waves, or electrical pulses depending on the network media over which the bits are transmitted. The destination host receives and decodes the signals to interpret the message.


Each message transmitted on a network must include a header that contains addressing information that identifies the source and destination hosts; otherwise, it cannot be delivered. Encapsulation is the process of adding this information to the pieces of data that make up the message. In addition to addressing, there may be other information in the header that ensures that the message is delivered to the correct application on the destination host.

Message pattern

Some messages require an acknowledgment before the next message can be sent. This type of request/response pattern is a common aspect of many networking protocols. However, there are other types of messages that may be simply streamed across the network, without concern as to whether they reach their destination.

5. Communication Standards (5.2) | Next Section Previous Section

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