When data are transmitted over a network, they are sent in steps. A single step includes certain actions that cannot take place at any other step. Each step has its own rules and procedures, or protocols.
There are four points to keep in mind about protocols:
There are many protocols.
Some protocols work only at particular OSI layers.
Some protocols work at multiple layers.
Protocols are consistent.
A protocol stack is a combination of protocols. Layers within the stack, which generally correspond to the OSI model, specify various protocols for handling a function or subsystem of the communication process. Each layer in the stack has its own set of rules.
protocol stack Multiple layers of protocols that work together.
The binding process is used to connect protocols, or protocol stacks, to the NIC. Protocols and NICs can be mixed and matched on an as-needed basis.
The binding order determines the sequence in which the operating system runs the protocol.
binding process The process of tying the protocols together to provide data with a route from the application level to the NIC.
binding order The sequence in which the operating system runs the protocol.
The computer industry has designated several kinds of protocol stacks as standard models. Hardware and software manufacturers can develop their products to meet any one or a combination of these protocol stacks. The most important protocol stacks include:
OSI protocol suite
Digital DECnet
Novell NetWare
AppleTalk
TCP/IP
IBM SNA
The Data Link Layer is divided into two sublayers:
Logical Link Control (LLC)
Media Access Control (MAC)
Media Access Control (MAC) The lower of two sublayers that make up the Data Link Layer. The MAC manages access to the physical network, delimits frames, and handles error control.