The ISO/OSI Reference Model

The International Organization for Standardization (ISO) Open Systems Interconnect (OSI) reference model defines seven layers of communications types and interfaces between them. (See Figure 1). Each layer depends on the service layer underneath, all the way down to the physical network hardware, such as computer network adapters, and cables connecting the cards together.An easy way to look at this is to compare this model with something that we use daily: tel. For you and me to talk when we are out of distance, we need a device like a phone. (The ISO / OSI model is the application layer.) Phones obviously are useless unless they have the ability to translate sound into electronic pulses that can be transferred over the wire and vice versa. (These features are found in the layers below the application layer.) Finally we get down to the physical connection: both must be plugged into an electrical outlet that is connected to a switch that is part of the network switch telephone network.If I make a call to lift the handset and dial your number. This number indicates the central office where to send my application and then what the central office phone to ring. Once the phone, start talking, and our session started. Conceptually, networks of computers work exactly the same way.