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Networking Basics

OSI Reference Model

Introduction to TCP/IP

LAN Basics

Understanding Switching

WAN Basics

Understanding Routing

What Is Layer 3 Switching?

Understanding VirtualLANs

Understanding Qualityof Service

Security Basics

Understanding VirtualPrivate Networks (VPN)

Voice TechnologyBasics

Network ManagementBasics

The Internet

OSI Reference Model

This lesson covers the OSI reference model. It is sometimesalso called ISO or 7 layer reference model. The model wasdeveloped by the International Standards Organization in theearly 1980's. It describes the principles for interconnectionof computer systems in an Open System Interconnection environment.

Contents
-The Layered Model

-Need of Layered Network Model

-Layer Functions

-Peer to PeerCommunications

-Layers 1 &2: Physical & Data Link Layers

- Network Layer

- Operations of NetworkLayer Protocol

- Static and Dynamic Routes

- LAN-to-LAN Routing

- Transport Layer

-Session, Presentation,and Application Layers

The Layered Model

The concept of layered communication is essential to ensuringinteroperability of all the pieces of a network. To introducethe process of layered communication, let’s take a lookat a simple example.

In this image, the goal is to get a messagefrom Location A to Location B. The sender doesn’t knowwhat language the receiver speaks – so the sender passesthe message on to a translator.
The translator, while not concerned with the content of themessage, will translate it into a language that may be globallyunderstood by most, if not all translators – thus itdoesn’t matter what language the final recipient speaks.In this example, the language is Dutch. The translator alsoindicates what the language type is, and then passes the messageto an administrative assistant.
The administrative assistant, while not concerned with thelanguage, or the message, will work to ensure the reliabledelivery of the message to the destination. In this example,she will attach the fax number, and then fax the documentto the destination – Location B.

The document is received by an administrativeassistant at Location B. The assistant at Location B may evencall the assistant at Location A to let her know the fax wasproperly received.
The assistant at Location B will then pass the message tothe translator at her office. The translator will see thatthe message is in Dutch. The translator, knowing that theperson to whom the message is addressed only speaks French,will translate the message so the recipient can properly readthe message. This completes the process of moving informationfrom one location to another.

Upon closer study of the process employedto communicate, you will notice that communication took placeat different layers. At layer 1, the administrative assistantscommunicated with each other. At layer 2, the translatorscommunicated with each other. And, at layer 3 the sender wasable to communicate with the recipient.

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