Steven C. Horii, MD

Figure 1. Diagram illustrates a layered communication model, the seven-layer ISO-OSI Reference Model. The top (Application) layer is the one that interacts with the user or the user's software. The bottom (Physical) layer supports the medium (eg, coaxial cable, fiber-optic, cable). In between are layers thathandle such tasks as encoding, breaking large data streams intosmaller packets, detecting and correcting errors, and controlling the flow of data over the medium. Two such stacks, one implemented in each device, are connected at the physical layer to provide device-to-device communication.