A conceptual organization of protocol groupings into a vertical stack. In such a stack, the lowest level protocols are placed at the bottom, forming the foundation upon which higher levels, or layers, are placed.The OSI Reference Model, for example, comprises seven layers, each of which is interrelated, providing services to those above and below.The lowest is Layer 1, the Physical Layer, which contains specifications for the electrical, optical, and mechanical aspects of the interface of the device to a physical transmission medium, such as twisted pair, coax, or fiber. The highest is Layer 7, the Application Layer, which contains specifications for services that support user and application tasks such as file transfer, interpretation of graphic formats and documents, and document processing. See also OSI Reference Model and protocol suite.
In networking, protocols are layered on top of each other, with each layer being responsible for a different aspect of communication. A protocol stack is a particular software implementation of a computer network protocol suite. The suite consists of the protocol definitions, whereas the stack is the software implementation.
Protocols within a suite are designed with a very specific purpose, and each protocol typically communicates with two others in the stack. The lowest protocol deals with the low-level physical interaction of hardware, whereas user applications deal with only the uppermost layers. Protocol stacks are generally divided into three parts dealing with applications, transport, and media.
Wikipedia. Protocol Stack. [Online, May 5, 2005.] Wikipedia Website. http://en.wikipedia.org/wiki/Protocol_stack.