The Rules (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.
The Three Elements (5.1.1)
The primary purpose of any network is to provide a method to communicate and share information. From the earliest primitive human societies to the most advanced technological societies of today, sharing information with others has been crucial for human advancement.
All communication begins with a message, or information, that must be sent from one individual or device to another. The methods used to send, receive, and interpret messages change over time as technology advances.
All communication methods have three elements in common. The first of these elements is the message source, or sender. Message sources are people or even electronic devices that need to communicate 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. The third element is called a transmission medium, or channel. It provides the pathway over which the message can travel from source to destination.
For example, in Figure 5-1, two people can communicate face-to-face. Prior to communicating, they must agree on how to communicate. If the communication is using voice, they must first agree on the language. Next, when they have a message to share, they must be able to format that message in a way that is understandable. If someone uses the English language but poor sentence structure, the message can easily be misunderstood. Each of these tasks describes protocols that are used to accomplish communication.
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Figure 5-1 Protocols for Face-to-Face Communications
Communication Protocols (5.1.2)
Communication in your daily life takes many forms and occurs in many environments. You have different expectations depending on whether you 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, you establish rules or agreements to govern the conversation. These agreements include the following:
What method of communication should you use? (See Figure 5-2.)
What language should you use? (See Figure 5-3.)
Do you need to confirm that your messages are received? (See Figure 5-4.)
Figure 5-2 shows two people agreeing on a method of communication.
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Figure 5-2 Method of Communication
Figure 5-3 shows two people agreeing on a common language to use for communication.
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Figure 5-3 Language Used for Communication
Figure 5-4 shows the communication between two people, including confirmation of the order.
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Figure 5-4 Confirmation of Communication
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.
Now think about the commonly accepted protocols for sending text messages to your friends.
Why Protocols Matter (5.1.3)
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 protocols include message format, message size, timing, encoding, encapsulation, and message patterns.
Table 5-1 Protocol Characteristics
Protocol Characteristic |
Description |
|---|---|
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, breaking the message into smaller pieces might be necessary to ensure that the message can be delivered reliably. |
Timing |
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. |
Encoding |
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 impulses depending on the network media over which the bits are transmitted. The destination host receives and decodes the signals to interpret the message. |
Encapsulation |
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, other information in the header may ensure 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, other types of messages may be simply streamed across the network, without concern as to whether they reach their destination. |
Lab—My Protocol Rules (5.1.4)
In this lab, you will complete the following objectives:
Relate computer network protocols to the rules that you use every day for various forms of communication.
Define the rules that govern how you send and interpret text messages.
Explain what would happen if the sender and receiver did not agree on the details of the protocol.