The protocol stack or network stack is an implementation of a computer networking protocol suite or protocol family. The terms are often used interchangeably; strictly speaking, the suite is the definition of the Communications protocols, and the stack is the software implementation of them.
Individual protocols within a suite are often designed with a single purpose in mind. This modularization makes design and evaluation easier. Because each protocol module usually communicates with two others, they are commonly imagined as layers in a stack of protocols. The lowest protocol always deals with low-level interaction with the communications hardware. Every higher layer adds more features and capability. User applications usually deal only with the topmost layers (see also OSI model).
In practical implementation, protocol stacks are often divided into three major sections: media, transport, and applications. A particular operating system or platform will often have two well-defined software interfaces: one between the media and transport layers, and one between the transport layers and applications. The media-to-transport interface defines how transport protocol software makes use of particular media and hardware types and is associated with a device driver. For example, this interface level would define how TCP/IP transport software would talk to the network interface controller. Examples of these interfaces include ODI and NDIS in the Microsoft Windows and DOS environment. The application-to-transport interface defines how application programs make use of the transport layers. For example, this interface level would define how a web browser program would talk to TCP/IP transport software. Examples of these interfaces include Berkeley sockets and System V STREAMS in Unix-like environments, and Winsock for Microsoft Windows.
Courtesy of Wikipedia
Cumberland Computer Services., LLC