أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11: 14 pm]

Rather than developing unique and separate systems for the delivery of each new service, the network industry as a whole has adopted a developmental framework that allows designers to understand current network platforms, and maintain them. At the same time, this framework is used to facilitate the development of new technologies to support future communications needs and technology enhancements.

Central to this developmental framework, is the use of generally-accepted models that describe network rules and functions.

Within this chapter, you will learn about these models, as well as the standards that make networks work, and how communication occurs

أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11:14 PM]
Class Activity – Designing a Communications System
Objectives
Explain the role of protocols and standards organizations in facilitating interoperability in network
communications.
Background / Scenario
You have just purchased a new automobile for your personal use. After driving the car for a week or so, you
find that it is not working correctly. Discussing the problem with several of your peers, you decide to take it to
an automotive repair facility that they highly recommend. It is the only repair facility located in close proximity.
When you arrive at the repair facility, you find that all the mechanics speak another language. You are having
difficulty explaining the automobile’s performance problems, but the repairs really need to be done. You are
not sure you can drive it back home to research other options.
You must find a way to work with the repair facility to ensure your automobile is fixed correctly.
How will you communicate with the mechanics? Design a communications model to ensure that the car is
properly repaired.
Reflection
What steps did you identify as important to communicating your repair request? Justify your answer.

أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11:15 PM]

A network 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. Networks can vary in size, shape, and function. 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, regardless of the method chosen, all communication 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 travels from source to destination.

Communication begins with a message, or information, that must be sent from a source to a destination. The sending of this 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 occurring. 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 protocols for using another medium, such as sending a letter.

For example, consider two people communicating face-to-face, as shown in Figure 1. 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. For example, if someone uses the English language, but poor sentence structure, the message can easily be misunderstood. Each of these tasks describe protocols put in place to accomplish communication. This is also true of computer communication, as shown in Figure 2.

Many different rules or protocols govern all methods of communication that exist in the world today.

أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11:15 PM]
Rule Establishment

Before communicating with one another, individuals must use established rules or agreements to govern the conversation. For example, consider Figure 1, protocols are necessary for effective communication. These rules, or protocols, must be followed in order for the message to be successfully delivered and understood. Protocols must account for the following requirements:

An identified sender and receiver

Common language and grammar

Speed and timing of delivery

Confirmation or acknowledgment 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 requirements shown in Figure 2. Each of these will be discussed in more detail.

أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11:16 PM]

One of the first steps to sending a message is encoding. Encoding is the process of converting information into another acceptable form, for transmission. Decoding reverses this process in order to interpret the information.

Imagine a person planning a holiday trip with a friend, and calling the friend to discuss the details of where they want to go, as shown in Figure 1. To communicate the message, she converts her thoughts into an agreed upon language. She then speaks the words using the sounds and inflections of spoken language that convey the message. Her friend listens to the description and decodes the sounds to understand the message he received.

Encoding also occurs in computer communication, as shown in Figure 2. Encoding between hosts must be in an appropriate format for the medium. 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 in order to interpret the message.

أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11:16 PM]
Message Formatting and Encapsulation

When a message is sent from source to destination, 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.

Letter writing is one of the most common forms of written human communication. For centuries, the agreed format for personal letters has not changed. In many cultures, a personal letter contains the following elements:

An identifier of the recipient

A salutation or greeting

The message content

A closing phrase

An identifier of the sender

In addition to having the correct format, most personal letters must also be enclosed in an envelope for delivery, as shown in Figure 1. The envelope has the address of the sender and receiver, each located at the proper place on the envelope. If the destination address and formatting are not correct, the letter is not delivered. The process of placing one message format (the letter) inside another message format (the envelope) is called encapsulation. De-encapsulation occurs when the process is reversed by the recipient and the letter is removed from the envelope.

A message that is sent over a computer network follows specific format rules for it to be delivered and processed. Just as a letter is encapsulated in an envelope for delivery, so too are computer messages. Each computer message is encapsulated in a specific format, called a frame, before it is sent over the network. A frame acts like an envelope; it provides the address of the destination and the address of the source host, as shown in Figure 2. Notice the frame has a source and destination in both the frame addressing portion and in the encapsulated message. The distinction between these two types of addresses will be explained later in this chapter.

The format and contents of a frame are determined by the type of message being sent and the channel over which it is communicated. Messages that are not correctly formatted are not successfully delivered to or processed by the destination host.

أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11:16 PM]

Another rule of communication is size. When people communicate with each other, the messages that they send are usually broken into smaller parts or sentences. These sentences are limited in size to what the receiving person can process at one time, as shown in Figure 1. An individual conversation may be made up of many smaller sentences to ensure that each part of the message is received and understood. Imagine what it would be like to read this course if it all appeared as one long sentence; it would not be easy to read and comprehend.

Likewise, when a long message is sent from one host to another over a network, it is necessary to break the message into smaller pieces, as shown in Figure 2. The rules that govern the size of the pieces, or frames, communicated across the network are very strict. They can also be different, depending on the channel used. Frames that are too long or too short are not delivered.

The size restrictions of frames require the source host to break a long message into individual pieces that meet both the minimum and maximum size requirements. The long message will be sent in separate frames, with each frame containing a piece of the original message. Each frame will also have its own addressing information. At the receiving host, the individual pieces of the message are reconstructed into the original message.

أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11:17 PM]
Message Timing

These are the rules of engagement for message timing.

Access Method

Access method determines when someone is able to send a message. If two people talk at the same time, a collision of information occurs and it is necessary for the two to back off and start again, as shown in Figure 1. Likewise, it is necessary for computers to define an access method. Hosts on a network need an access method to know when to begin sending messages and how to respond when collisions occur.

Flow Control

Timing also affects how much information can be sent and the speed that it can be delivered. If one person speaks too quickly, it is difficult for the other person to hear and understand the message, as shown in Figure 2. In network communication, source and destination hosts use flow control methods to negotiate correct timing for successful communication.

Response Timeout

If a person asks a question and does not hear a response within an acceptable amount of time, the person assumes that no answer is coming and reacts accordingly, as shown in Figure 3. The person may repeat the question, or may go on with the conversation. Hosts on the network also have rules that specify how long to wait for responses and what action to take if a response timeout occurs.

أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11:17 PM]
Message Delivery Options

A message can be delivered in different ways, as shown in Figure 1. 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.

There are also times when the sender of a message needs to be sure that the message is delivered successfully to the destination. In these cases, it is necessary for the recipient to return an acknowledgment to the sender. If no acknowledgment is required, the delivery option is referred to as unacknowledged.

Hosts on a network use similar delivery options to communicate, as shown in Figure 2.

A one-to-one delivery option is referred to as a unicast, meaning there is only a single destination for the message.

When a host needs to send messages using a one-to-many delivery option, it is referred to as a multicast. Multicasting is the delivery of the same message to a group of host destinations simultaneously.

If all hosts on the network need to receive the message at the same time, a broadcast may be used. Broadcasting represents a one-to-all message delivery option. Some protocols use a special multicast message that is sent to all devices, making it essentially the same as a broadcast. Additionally, hosts may be required to acknowledge the receipt of some messages while not needing to acknowledge others.

أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11:18 PM]

A message can be delivered in different ways, as shown in Figure 1. 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.

There are also times when the sender of a message needs to be sure that the message is delivered successfully to the destination. In these cases, it is necessary for the recipient to return an acknowledgment to the sender. If no acknowledgment is required, the delivery option is referred to as unacknowledged.

Hosts on a network use similar delivery options to communicate, as shown in Figure 2.

A one-to-one delivery option is referred to as a unicast, meaning there is only a single destination for the message.

When a host needs to send messages using a one-to-many delivery option, it is referred to as a multicast. Multicasting is the delivery of the same message to a group of host destinations simultaneously.

If all hosts on the network need to receive the message at the same time, a broadcast may be used. Broadcasting represents a one-to-all message delivery option. Some protocols use a special multicast message that is sent to all devices, making it essentially the same as a broadcast. Additionally, hosts may be required to acknowledge the receipt of some messages while not needing to acknowledge others.

أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11:18 PM]

A group of inter-related protocols necessary to perform a communication function is called a protocol suite. Protocol suites are implemented by hosts and networking devices in software, hardware or both.

One of the best ways to visualize how the protocols within a suite interact is to view the interaction as a stack. A protocol stack shows how the individual protocols within a suite are implemented. The protocols are viewed in terms of layers, with each higher level service depending on the functionality defined by the protocols shown in the lower levels. The lower layers of the stack are concerned with moving data over the network and providing services to the upper layers, which are focused on the content of the message being sent.

As the figure shows, we can use layers to describe the activity occurring in our face-to-face communication example. At the bottom, the physical layer, we have two people, each with a voice that can say words out loud. In the middle, the rules layer, we have an agreement to speak in a common language. At the top, the content layer, there are words that are actually spoken. This is the content of the communication.

أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11:19 PM]
Network Protocols

At the human level, some communication rules are formal and others are simply understood based on custom and practice. For devices to successfully communicate, a network protocol suite must describe precise requirements and interactions. Networking protocols define a common format and set of rules for exchanging messages between devices. Some common networking protocols are Hypertext Transfer Protocol (HTTP), Transmission Control Protocol (TCP), and Internet Protocol (IP).

Note: IP in this course refers to both the IPv4 and IPv6 protocols. IPv6 is the most recent version of IP and the replacement for the more common IPv4.

The figures illustrate networking protocols that describe the following processes:

How the message is formatted or structured, as shown in Figure 1.

The process by which networking devices share information about pathways with other networks, as shown in Figure 2.

How and when error and system messages are passed between devices, as shown in Figure 3.

The setup and termination of data transfer sessions, as shown in Figure 4.

أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11:19 PM]
Protocol Interaction

Communication between a web server and web client is an example of an interaction between several protocols. The protocols shown in the figure include:

HTTP - is an application protocol that 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.

TCP - is the transport protocol that manages the individual conversations. TCP divides the HTTP messages into smaller pieces, called segments. These segments are sent between the web server and client processes running at the destination host. TCP is also responsible for controlling the size and rate at which messages are exchanged between the server and the client.

IP - is responsible for taking the formatted segments from TCP, encapsulating them into packets, assigning them the appropriate addresses, and delivering them to the destination host.

Ethernet - is a network access protocol that describes two primary functions: communication over a data link and the physical transmission of data on the network media. Network access protocols are responsible for taking the packets from IP and formatting them to be transmitted over the media.

أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11:20 PM]
Protocol Suites and Industry Standards

A protocol suite is a set of protocols that work together to provide comprehensive network communication services. A protocol suite may be specified by a standards organization or developed by a vendor. Protocol suites, like the four shown in the figure, can be a bit overwhelming. However, this course will only cover the protocols of the TCP/IP protocol suite.

The TCP/IP protocol suite is an open standard, meaning these protocols are freely available to the public, and any vendor is able to implement these protocols on their hardware or in their software.

A standards-based protocol is a process that has been endorsed by the networking industry and approved by a standards organization. The use of standards in developing and implementing protocols ensures that products from different manufacturers can interoperate successfully. If a protocol is not rigidly observed by a particular manufacturer, their equipment or software may not be able to successfully communicate with products made by other manufacturers.

Some protocols are proprietary which means one company or vendor controls the definition of the protocol and how it functions. Examples of proprietary protocols are AppleTalk and Novell Netware, which are legacy protocol suites. It is not uncommon for a vendor (or group of vendors) to develop a proprietary protocol to meet the needs of its customers and later assist in making that proprietary protocol an open standard.

For example, click here to view a video presentation by Bob Metcalfe describing the story of how Ethernet was developed.

أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11:20 PM]
Development of TCP/IP

The first packet switching network and predecessor to today’s Internet was the Advanced Research Projects Agency Network (ARPANET), which came to life in 1969 by connecting mainframe computers at four locations. ARPANET was funded by the U.S. Department of Defense for use by universities and research laboratories.

Click through the timeline in the figure to see details about the development of other network protocols and applications.

أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11:21 PM]

Today, the TCP/IP protocol suite includes many protocols, as shown in the figure. Click each protocol to view the acronym’s translation and description. The individual protocols are organized in layers using the TCP/IP protocol model: Application, Transport, Internet, and Network Access Layers. TCP/IP protocols are specific to the Application, Transport, and Internet layers. The network access layer protocols are responsible for delivering the IP packet over the physical medium. These lower layer protocols are developed by various standards organizations.

The TCP/IP protocol suite is implemented as a TCP/IP stack on both the sending and receiving hosts to provide end-to-end delivery of applications over a network. The Ethernet protocols are used to transmit the IP packet over the physical medium used by the LAN.

أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11:21 PM]

Figures 1 and 2 demonstrate the complete communication process using an example of a web server transmitting data to a client. This process and these protocols will be covered in more detail in later chapters.

Click the Play button to view the animated demonstrations:

1. In Figure 1, the animation begins with the web server preparing the Hypertext Markup Language (HTML) page as data to be sent.

2. The application protocol HTTP header is added to the front of the HTML data. The header contains various information, including the HTTP version the server is using and a status code indicating it has information for the web client.

3. The HTTP application layer protocol delivers the HTML-formatted web page data to the transport layer. The TCP transport layer protocol is used to manage individual conversations, in this example between the web server and web client.

4. Next, the IP information is added to the front of the TCP information. IP assigns the appropriate source and destination IP addresses. This information is known as an IP packet.

5. The Ethernet protocol adds information to both ends of the IP packet, known as a data link frame. This frame is delivered to the nearest router along the path towards the web client. This router removes the Ethernet information, analyzes the IP packet, determines the best path for the packet, inserts the packet into a new frame, and sends it to the next neighboring router towards the destination. Each router removes and adds new data link information before forwarding the packet.

6. This data is now transported through the internetwork, which consists of media and intermediary devices.

7. In Figure 2, the animation begins with the client receiving the data link frames that contain the data. Each protocol header is processed and then removed in the opposite order it was added. The Ethernet information is processed and removed, followed by the IP protocol information, the TCP information, and finally the HTTP information.

8. The web page information is then passed on to the client’s web browser software.

أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11:22 PM]

Open standards encourage interoperability, competition, and innovation. They also guarantee that no single company’s product can monopolize the market, or have an unfair advantage over its competition.

A good example of this is when purchasing a wireless router for the home. There are many different choices available from a variety of vendors, all of which incorporate standard protocols such as IPv4, DHCP, 802.3 (Ethernet), and 802.11 (Wireless LAN). These open standards also allow a client running Apple’s OS X operating system to download a web page from a web server running the Linux operating system. This is because both operating systems implement the open standard protocols, such as those in the TCP/IP protocol suite.

Standards organizations are important in maintaining an open Internet with freely accessible specifications and protocols that can be implemented by any vendor. A standards organization may draft a set of rules entirely on its own or in other cases may select a proprietary protocol as the basis for the standard. If a proprietary protocol is used, it usually involves the vendor who created the protocol.

Standards organizations are usually vendor-neutral, non-profit organizations established to develop and promote the concept of open standards.

Click the logo in the figure to visit the website for each standards organization.

أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11:22 PM]
Internet Standards

Standards organizations are usually vendor-neutral, non-profit institutions established to develop and promote the concept of open standards. Various organizations have different responsibilities for promoting and creating standards for the TCP/IP protocol.

Standards organizations shown in Figure 1 include:

Internet Society (ISOC) – Responsible for promoting the open development and evolution of Internet use throughout the world.

Internet Architecture Board (IAB) - Responsible for the overall management and development of Internet standards.

Internet Engineering Task Force (IETF) - Develops, updates, and maintains Internet and TCP/IP technologies. This includes the process and documents for developing new protocols and updating existing protocols know as Request for Comments (RFC) documents.

Internet Research Task Force (IRTF) - Focused on long-term research related to Internet and TCP/IP protocols such as Anti-Spam Research Group (ASRG), Crypto Forum Research Group (CFRG), and Peer-to-Peer Research Group (P2PRG).

Standards organizations shown in Figure 2 include:

Internet Corporation for Assigned Names and Numbers (ICANN) - Based in the United States, coordinates IP address allocation, the management of domain names, and assignment of other information used TCP/IP protocols.

Internet Assigned Numbers Authority (IANA) - Responsible for overseeing and managing IP address allocation, domain name management, and protocol identifiers for ICANN.

أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11:23 PM]
Electronics and Communications Standard Organizations

Other standard organizations have responsibilities for promoting and creating the electronic and communication standards used to deliver the IP packets as electronic signals over a wired or wireless medium.

Institute of Electrical and Electronics Engineers (IEEE, pronounced “I-triple-E”) – Organization of electrical engineering and electronics dedicated to advancing technological innovation and creating standards in a wide area of industries including power and energy, healthcare, telecommunications, and networking. Figure 1 shows several of the standards related to networking.

Electronic Industries Alliance (EIA) - Best known for its standards related to electrical wiring, connectors, and the 19-inch racks used to mount networking equipment.

Telecommunications Industry Association (TIA) - Responsible for developing communication standards in a variety of areas including radio equipment, cellular towers, Voice over IP (VoIP) devices, satellite communications, and more. Figure 2 shows an example of an Ethernet cable meeting TIA/EIA standards.

International Telecommunications Union-Telecommunication Standardization Sector (ITU-T) - One of the largest and oldest communication standard organizations. The ITU-T defines standards for video compression, Internet Protocol Television (IPTV), and broadband communications, such as a digital subscriber line (DSL).

أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11:23 PM]
Lab - Researching Networking Standards

In this lab, you will complete the following objectives:

Part 1: Research Networking Standards Organizations

Part 2: Reflect on Internet and Computer Networking Experience

Lab - Researching Networking Standards

أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11:23 PM]

The benefits to using a layered model to describe network protocols and operations include:

Assisting 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.

Fostering competition because products from different vendors can work together.

Preventing technology or capability changes in one layer from affecting other layers above and below.

Providing a common language to describe networking functions and capabilities.

As shown in the figure, the TCP/IP model and the Open Systems Interconnection (OSI) model are the primary models used when discussing network functionality. They each represent a basic type of layered networking models:

Protocol model - This type of model closely matches the structure of a particular protocol suite. 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. TCP/IP is also used as a reference model.

Reference model - This type of model provides consistency within all types of network protocols and services by describing what has to be done at a particular layer, but not prescribing how it should be accomplished. The OSI model is a widely known internetwork reference model, but is also a protocol model for the OSI protocol suite.

أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11:24 PM]

The OSI model provides an extensive list of functions and services that can occur at each layer. It also describes the interaction of each layer with the layers directly above and below. The TCP/IP protocols discussed in this course are structured around both the OSI and TCP/IP models. Click each layer of the OSI model to view the details.

The functionality of each layer and the relationship between layers will become more evident throughout this course as the protocols are discussed in more detail.

Note: Whereas the TCP/IP model layers are referred to only by name, the seven OSI model layers are more often referred to by number rather than by name. For instance, the physical layer is referred to as Layer 1 of the OSI model.

أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11:24 PM]
The TCP/IP Protocol Model

The TCP/IP protocol model for internetwork communications was created in the early 1970s and is sometimes referred to as the Internet model. As shown in the figure, it defines four categories of functions that must occur for communications to be successful. The architecture of the TCP/IP protocol suite follows the structure of this model. Because of this, the Internet model is commonly referred to as the TCP/IP model.

Most protocol models describe a vendor-specific protocol stack. Legacy protocol suites, such as Novell Netware and AppleTalk, are examples of vendor-specific protocol stacks. Because the TCP/IP model is an open standard, one company does not control the definition of the model. The definitions of the standard and the TCP/IP protocols are discussed in a public forum and defined in a publicly available set of RFCs.

أَبْدُرَهْمَنْ إِبْن أَبْدُسَطَّرْAbdurahmon To‘ychiyev, [1/31/2024 11:24 PM]

The protocols that make up the TCP/IP protocol suite can also be described in terms of the OSI reference model. In the OSI model, the network access layer and the application layer of the TCP/IP model are further divided to describe discrete functions that must occur at these layers.

At the network access layer, the TCP/IP protocol suite does not specify which protocols to use when transmitting over a physical medium; it only describes the handoff from the internet layer to the physical network protocols. OSI Layers 1 and 2 discuss the necessary procedures to access the media and the physical means to send data over a network.

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 a number of 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 products that operate on networks.