The OSI Reference Model

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.

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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

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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.

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TCP/IP Protocol Suite

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.

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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.

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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.

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Rules that Govern Communications

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.

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