Communication Principles

In this sample chapter from Networking Essentials Companion Guide, you will explore the protocols of network communication and how to troubleshoot problems in your network.

Objectives

Upon completion of this chapter, you will be able to answer the following questions:

• What are network communication protocols?

• What are network communication standards?

• What are the differences and similarities of the OSI and TCP/IP models?

• How do the OSI model‛s Layer 1 and Layer 2 function in an Ethernet network?

Key Terms

This chapter uses the following key terms. You can find the definitions in the Glossary.

Ethernet page 103

Institute of Electrical and Electronic Engineers (IEEE)

International Organization for Standardization (ISO)

Internet Engineering Task Force (IETF)

protocol

protocol suite

reference model

Request for Comments (RFC)

Introduction (5.0.1)

When you talk with someone, you are communicating. When you mail a card to a relative, you are communicating. You probably don‛t think much about the rules of communication when you do these two things. But there are rules, and good communication happens only when all parties know and follow those rules. It is the same with devices on a network. This chapter explains the rules, which are called protocols, of network communication. When you understand the various protocols and how they work with other protocols, you not only will understand how networks and the Internet work but also be able to troubleshoot problems in your own network.

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.

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.

Figure 5-3 shows two people agreeing on a common language to use for communication.

Figure 5-4 shows the communication between two people, including confirmation of the order.

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

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.

Communication Standards (5.2)

Communication standards are required in all aspects of human communications such as when addressing an envelope. There is a standard regarding the placement of the sender‛s address, destination address, and even where you put the stamp. Network communication also requires standards to ensure that all the devices in the network use the same rules to send and receive information.

Video—Devices in a Bubble (5.2.1)

Refer to the online course to view this video.

The Internet and Standards (5.2.2)

With the increasing number of new devices and technologies coming online, how is it possible to manage all the changes and still reliably deliver services such as email? The answer is Internet standards.

A standard is a set of rules that determine how something must be done. Networking and Internet standards ensure that all devices connecting to the network implement the same set of rules or protocols in the same manner. Using standards, different types of devices are able to send information to each other over the Internet. For example, the way in which an email is formatted, forwarded, and received by all devices is done according to a standard. If one person sends an email via a personal computer, another person can use a mobile phone to receive and read the email as long as the mobile phone uses the same standards as the personal computer.

Network Standards Organizations (5.2.3)

An Internet standard is the end result of a comprehensive cycle of discussion, problem solving, and testing. These different standards are developed, published, and maintained by a variety of organizations, as shown in Figure 5-5. When a new standard is proposed, each stage of the development and approval process is recorded in a numbered Request for Comments (RFC) document so that the evolution of the standard is tracked. RFCs for Internet standards are published and managed by the Internet Engineering Task Force (IETF).

Other standards organizations that support the Internet are shown in Figure 5-5.

Network Communication Models (5.3)

Network communication models help you understand the various components and protocols used in network communications. These models help you see the function of each protocol and their relationship to other protocols.

Video—Network Protocols (5.3.1)

Refer to the online course to view this video.

Video—The Protocol Stack (5.3.2)

Refer to the online course to view this video.

The Protocol Stack (5.3.3)

Successful communication between hosts requires interaction between many protocols. These protocols are implemented in software and hardware that are installed on each host and networking device.

The interaction between the different protocols on a device can be illustrated as a protocol stack, as shown in Figure 5-6. A stack illustrates the protocols as a layered hierarchy, with each higher-level protocol depending on the services of the protocols shown in the lower levels.

The separation of functions enables each layer in the stack to operate independently of others. For example, you can use your laptop computer connected to a cable modem at home to access your favorite website, or you can view the same website on your laptop using a wireless connection at the library. The function of the web browser is not affected by the change in the physical location or the method of connectivity.

The protocols in Figure 5-6 are described as follows:

• Hypertext Transfer Protocol (HTTP)—This protocol governs the way a web server and a web client interact. HTTP defines the content and formatting of the requests and responses that are exchanged between the client and server. Both the client and the web server software implement HTTP as part of the application. HTTP relies on other protocols to govern how the messages are transported between the client and server.

• Transmission Control Protocol (TCP)—This protocol manages the individual conversations. TCP is responsible for guaranteeing the reliable delivery of the information and managing flow control between the end devices.

• Internet Protocol (IP)—This protocol is responsible for delivering messages from the sender to the receiver. IP is used by routers to forward the messages across multiple networks.

• Ethernet—This protocol is responsible for the delivery of messages from one NIC to another NIC on the same Ethernet local-area network (LAN).

The TCP/IP Model (5.3.4)

Layered models help you visualize how the various protocols work together to enable network communications. A layered model depicts the operation of the protocols occurring within each layer, as well as the interaction with the layers above and below it. The layered model has many benefits:

• Assists in protocol design, because protocols that operate at a specific layer have defined information that they act upon and a defined interface to the layers above and below

• Fosters competition because products from different vendors can work together

• Enables technology changes to occur at one level without affecting the other levels

• Provides a common language to describe networking functions and capabilities

The first layered model for internetwork communications was created in the early 1970s and is referred to as the Internet model. It defines four categories of functions that must occur in order for communications to be successful. The suite of TCP/IP protocols that are used for Internet communications follows the structure of this model, as shown in Table 5-2. Because of this, the Internet model is commonly referred to as the TCP/IP model.

Table 5-2 The Layers of the TCP/IP Model

The OSI Reference Model (5.3.5)

Two basic types of models are used to describe the functions that must occur in order for network communications to be successful: protocol models and reference models.

• Protocol model—This model closely matches the structure of a particular protocol suite. A protocol suite includes the set of related protocols that typically provide all the functionality required for people to communicate with the data network. The TCP/IP model is a protocol model because it describes the functions that occur at each layer of protocols within the TCP/IP suite.

• Reference model—This type of model describes the functions that must be completed at a particular layer but does not specify exactly how a function should be accomplished. A reference model is not intended to provide a sufficient level of detail to define precisely how each protocol should work at each layer. The primary purpose of a reference model is to aid in clearer understanding of the functions and processes necessary for network communications.

The most widely known internetwork reference model was created by the Open Systems Interconnection (OSI) project at the International Organization for Standardization (ISO). It is used for data network design, operation specifications, and troubleshooting. This model is commonly referred to as the OSI model. The OSI layers are described in Table 5-3.

Table 5-3 The Layers of the OSI Model

Upper and Lower Layers of the OSI Model (5.3.6)

You can visualize how data moves across a network by using the seven layers of the OSI model, as shown in Table 5-3. The OSI model breaks down network communication into multiple processes, as shown in Table 5-4. Each process is a small part of the larger task.

Table 5-4 Common Components of the Layers of the OSI Model

For example, in a vehicle manufacturing plant, the entire vehicle is not assembled by one person. Rather, the vehicle moves from station to station where specialized teams add specific components. The complex task of assembling a vehicle is made easier by breaking it into manageable and logical tasks. This process also makes troubleshooting easier. When a problem occurs in the manufacturing process, it is possible to isolate the problem to the specific task where the defect was introduced and then fix that problem.

In a similar manner, the OSI model helps you troubleshoot by focusing on a specific layer to identify and resolve network problems. Networking teams often refer to different functions occurring on a network by the number of the OSI model layer that specifies that functionality. For example, the process of encoding the data bits for transmission across the media occurs at Layer 1, the physical layer. The formatting of data so it can be interpreted by the network connection in your laptop or phone is described at Layer 2, the data link layer.

OSI Model and TCP/IP Model Comparison (5.3.7)

Because TCP/IP is the protocol suite in use for Internet communications, why do you need to learn the OSI model as well? The TCP/IP model is a method of visualizing the interactions of the various protocols that make up the TCP/IP protocol suite. It does not describe general functions that are necessary for all networking communications. It describes the networking functions specific to those protocols in use in the TCP/IP protocol suite. For example, at the network access layer, the TCP/IP protocol suite does not specify which protocols to use when transmitting over a physical medium, nor the method of encoding the signals for transmission. OSI Layers 1 and 2 discuss the necessary procedures to access the media and the physical means to send data over a network.

The protocols that make up the TCP/IP protocol suite can be described in terms of the OSI reference model. The functions that occur at the Internet layer in the TCP/IP model are contained in the network layer of the OSI model, as shown in Figure 5-7. The transport layer functionality is the same between both models. However, the network access layer and the application layer of the TCP/IP model are further divided in the OSI model to describe discrete functions that must occur at these layers.

The key similarities are in the transport and network layers; however, the two models differ in how they relate to the layers above and below each layer:

• OSI Layer 3, the network layer, maps directly to the TCP/IP Internet layer. This layer is used to describe protocols that address and route messages through an internetwork.

• OSI Layer 4, the transport layer, maps directly to the TCP/IP transport layer. This layer describes general services and functions that provide ordered and reliable delivery of data between source and destination hosts.

• The TCP/IP application layer includes several protocols that provide specific functionality to a variety of end-user applications. The OSI model Layers 5, 6, and 7 are used as references for application software developers and vendors to produce applications that operate on networks.

• Both the TCP/IP and OSI models are commonly used when referring to protocols at various layers. Because the OSI model separates the data link layer from the physical layer, it is commonly used when referring to these lower layers.

Ethernet (5.4)

When you are connecting to a network using a wired interface, you are using the Ethernet protocol. Even most wireless networks ultimately connect to a wired Ethernet network. Ethernet is an important data link layer protocol used in LANs and most wide-area networks (WANs).

The Rise of Ethernet (5.4.1)

In the early days of networking, each vendor used its own proprietary methods of interconnecting network devices and networking protocols. If you bought equipment from different vendors, there was no guarantee that the equipment would work together. Equipment from one vendor might not communicate with equipment from another.

As networks became more widespread, standards were developed that defined rules by which network equipment from different vendors operated. Standards are beneficial to networking in many ways:

• Facilitate design

• Simplify product development

• Promote competition

• Provide consistent interconnections

• Facilitate training

• Provide more vendor choices for customers

There is no official local-area networking standard protocol, but over time, one technology, Ethernet, has become more common than the others. Ethernet protocols define how data is formatted and how it is transmitted over the wired network. The Ethernet standards specify protocols that operate at Layer 1 and Layer 2 of the OSI model. Ethernet has become the de facto standard, which means that it is the technology used by almost all wired local-area networks, as shown in Figure 5-8.

Ethernet Evolution (5.4.2)

The Institute of Electrical and Electronic Engineers, or IEEE (pronounced “eye-triple-e”), maintains the networking standards, including Ethernet and wireless standards. IEEE committees are responsible for approving and maintaining the standards for connections, media requirements, and communication protocols. Each technology standard is assigned a number that refers to the committee that is responsible for approving and maintaining the standard. The committee responsible for Ethernet standards is 802.3.

Since the creation of Ethernet in 1973, standards have evolved for specifying faster and more flexible versions of the technology. This ability for Ethernet to improve over time is one of the main reasons that it has become so popular. Each version of Ethernet has an associated standard. For example, 802.3 100BASE-T represents the 100 megabit Ethernet using twisted-pair cable standards. The standard notation translates as follows:

• 100 is the speed in Mbps.

• BASE stands for baseband transmission.

• T stands for the type of cable—in this case, twisted-pair.

Early versions of Ethernet were relatively slow at 10 Mbps. The latest versions of Ethernet operate at 10 gigabits per second and more. Imagine how much faster these new versions are than the original Ethernet networks.

Video—Ethernet Addressing (5.4.3)

Refer to the online course to view this video.

The Ethernet MAC Address (5.4.4)

All communication requires a way to identify the source and destination. The source and destination in human communication are represented by names.

When your name is called, you listen to the message and respond. Other people in the room may hear the message, but they ignore it because it is not addressed to them.

On Ethernet networks, a similar method exists for identifying source and destination hosts. Each host connected to an Ethernet network is assigned a physical address that serves to identify the host on the network.

Every Ethernet network interface has a physical address assigned to it when it is manufactured. This address is known as the Media Access Control (MAC) address. The MAC address identifies each source and destination host on the network, as shown in Figure 5-9.

Lab—Determine the MAC Address of a Host (5.4.5)

In this lab, you will complete the following objectives:

• Determine the MAC address of a Windows computer on an Ethernet network using the ipconfig /all command.

• Analyze a MAC address to determine the manufacturer.

Summary (5.5)

The following is a summary of each topic in the chapter:

• The Rules—All communication methods have three elements in common. The first is the message source, or sender. Message sources are people or electronic devices that need to communicate a message to other individuals or devices. The second is the destination, or receiver, of the message. The destination receives the message and interprets it. The third is the transmission medium, or channel. It provides the pathway over which the message can travel from source to destination.

  Among the protocols that govern successful human communication are an identified sender and receiver, an agreed-upon method of communicating, common language and grammar, speed and timing of delivery, and confirmation or acknowledgment requirements. Networking protocols define the message format, message size, timing, encoding, and message patterns over the local network.

• Communication Standards—Networking and Internet standards ensure that all devices connecting to the network implement the same set of rules or protocols in the same manner. Using standards, different types of devices are able to send information to each other over the Internet. These standards are developed, published, and maintained by a variety of organizations. When a new standard is proposed, each stage of the development and approval process is recorded in a numbered RFC document so that the evolution of the standard is tracked. RFCs for Internet standards are published and managed by the IETF.

• Network Communication Models—A stack illustrates the protocols as a layered hierarchy, with each higher-level protocol depending on the services of the protocols shown in the lower levels. The separation of functions enables each layer in the stack to operate independently of others.

  The layered model has many benefits:

  • Assists in protocol design, because protocols that operate at a specific layer have defined information that they act upon and a defined interface to the layers above and below

  • Fosters competition because products from different vendors can work together

  • Enables technology changes to occur at one level without affecting the other levels

  • Provides a common language to describe networking functions and capabilities

  The suite of TCP/IP protocols used for Internet communications follows the structure of the stack model. The two basic types of models to describe the functions that must occur for network communications to be successful are protocol models and reference models. The most widely known internetwork reference model is the OSI model. The OSI model breaks down network communications into multiple processes. Each process is a small part of the larger task.

  The protocols that make up the TCP/IP protocol suite can be described in terms of the OSI reference model. The functions that occur at the Internet layer in the TCP/IP model are contained in the network layer of the OSI model. The transport layer functionality is the same between both models. However, the network access layer and the application layer of the TCP/IP model are further divided in the OSI model to describe discrete functions that must occur at these layers.

• Ethernet—There is no official LAN standard protocol, but over time, Ethernet has become more common than the others. Ethernet protocols define how data is formatted and how it is transmitted over the wired network. The Ethernet standards specify protocols that operate at Layer 1 and Layer 2 of the OSI model. Ethernet standards have evolved for specifying faster and more flexible versions of the technology. Each version of Ethernet has an associated standard. Each host connected to an Ethernet network is assigned a physical address that serves to identify the host on the network. Every Ethernet network interface has a physical address assigned to it when it is manufactured. This address is known as the MAC address. The MAC address identifies each source and destination host on the network.

Practice

The following labs provide practice with the topics introduced in this chapter.

Labs

Lab—My Protocol Rules (5.1.4)

Lab—Determine the MAC Address of a Host (5.4.5)

Check Your Understanding Questions

Complete all the review questions listed here to test your understanding of the topics and concepts in this chapter. Appendix A, “Answers to the ‘Check Your Understanding‛ Questions,” lists the answers.

1. Which organization publishes and manages the Request for Comments (RFC) documents?

   • TIA/EIA

   • IETF

   • ISO

   • IEEE

2. What identifier is used at the data link layer to uniquely identify an Ethernet device?

   • MAC address

   • Sequence number

   • IP address

   • UDP port number

   • TCP port number

3. Which layers of the OSI model are comparable in function to the application layer of the TCP/IP model? (Choose three.)

   • Data link

   • Transport

   • Network

   • Presentation

   • Application

   • Session

   • Physical

4. Which term refers to a common set of rules that are developed to define rules by which network equipment from different vendors can interoperate?

   • Domain

   • Standard

   • Model

   • Protocol

5. Which standards organization publishes current Ethernet standards?

   • ANSI

   • CCITT

   • IEEE

   • EIA/TIA

6. Which statement describes a MAC address?

   • It contains two portions: the network portion and a host portion.

   • It is 128 bits in length.

   • It identifies the source and destination addresses of hosts on the Internet.

   • It is a physical address assigned to an Ethernet NIC by the manufacturer.

7. Which elements do all communication methods have in common? (Choose three.)

   • Message priority

   • Message source

   • Transmission medium

   • Message type

   • Message data

   • Message destination

8. Which layers of the OSI model specify protocols that are associated with Ethernet standards? (Choose two.)

   • Physical layer

   • Transport layer

   • Session layer

   • Data link layer

   • Network layer

9. Which layer of the OSI model defines services to segment and reassemble data for individual communications between end devices?

   • Network

   • Presentation

   • Transport

   • Session

   • Application

10. Which statement defines a data communications protocol?

    • An alliance of network device manufacturers

    • A set of product standards for types of network devices

    • An exchange agreement of network devices among vendors

    • A set of rules that govern the communication process