The
OSI model defines distinct layers related to packaging, sending, and
receiving data transmissions in a network. A layered set of related
protocols actually carries out these services. This layered set of
protocols running on a network is called a protocol stack. Together,
the protocols in the stack handle all tasks required in packaging,
sending, and receiving transmissions. Several protocol stacks are
designated as standard protocol models. Some of the common protocol
stacks are TCP/IP, IPX/SPX, and AppleTalk. Protocols exist at each
layer of these stacks, performing the tasks specified by that layer.
Generally, however, the responsibility for performing specific
communication tasks in the network is assigned to protocols working
as one of three types:
application protocols, transport protocols, and network protocols.
Application Protocols
Application protocols provide data exchange between applications in
a network. Examples of common application protocols include File
Transfer Protocol (FTP) and Simple Mail Transfer Protocol (SMTP).
Transport Protocols
Transport protocols provide for communication sessions between
computers and ensure that data moves reliably between computers. A
common transport protocol is Transmission Control Protocol (TCP).
Network
Protocols
Network protocols provide what are called
link services.
These protocols define the rules for communicating in a particular
network environment. A common protocol that provides network
services is Internet Protocol (IP).
