What is Network Protocol?
A protocol is a set of rules that governs the communications
between computers on a network. In order for two computers to talk to each
other, they must be speaking the same language. Many different types of network
protocols and standards are required to ensure that your computer (no matter
which operating system, network card, or application you are using) can
communicate with another computer located on the next desk or half-way around
the world. The OSI (Open Systems Interconnection) Reference Model defines seven
layers of networking protocols.
OSI (Open Systems Interconnection)
OSI
(Open Systems Interconnection) is a standard description or "reference
model" for how messages should be transmitted between any two points in a
telecommunication network. Its
purpose is to guide product implementors so that their products will
consistently work with other products. The reference model defines seven layers
of functions that take place at each end of a communication. Although OSI is
not always strictly adhered to in terms of keeping related functions together
in a well-defined layer, many if not most products involved in
telecommunication make an attempt to describe themselves in relation to the OSI
model. It is also valuable as a single reference view of communication that
furnishes everyone a common ground for education and discussion.
Developed
by representatives of major computer and telecommunication companies beginning
in 1983, OSI was originally intended to be a detailed specification of
interfaces. Instead, the committee decided to establish a common reference
model for which others could develop detailed interfaces that in turn could
become standards. OSI was officially adopted as an international standard by
the International Organization of Standards (ISO). Currently, it is
Recommendation X.200 of the ITU-TS.
The
main idea in OSI is that the process of communication between two end points in
a telecommunication network can be divided into layers, with each layer adding
its own set of special, related functions. Each communicating user or program
is at a computer equipped with these seven layers of function. So, in a given
message between users, there will be a flow of data through each layer at one
end down through the layers in that computer and, at the other end, when the
message arrives, another flow of data up through the layers in the receiving computer
and ultimately to the end user or program. The actual programming and hardware
that furnishes these seven layers of function is usually a combination of the
computer operating system,
applications (such as your Web browser), TCP/IP or alternative transport and network
protocols, and the software and hardware that enable you to put a signal on one
of the lines attached to your computer.
OSI
divides telecommunication into seven layers. The layers are in two groups. The
upper four layers are used whenever a message passes from or to a user. The
lower three layers (up to the network layer) are used when any message passes
through the host computer. Messages intended for this computer pass to the
upper layers. Messages destined for some other host are not passed up to the
upper layers but are forwarded to another host. The seven layers are:
Layer 7: The application
layer...This
is the layer at which communication partners are identified, quality of service
is identified, user authentication and privacy are considered, and any
constraints on data syntax are identified. (This layer is not the application itself, although some
applications may perform application layer functions.)
Layer 6: The presentation
layer...This
is a layer, usually part of an operating system, that converts incoming and
outgoing data from one presentation format to another (for example, from a text
stream into a popup window with the newly arrived text). Sometimes called the
syntax layer.
Layer 5: The session layer...This layer sets up,
coordinates, and terminates conversations, exchanges, and dialogs between the
applications at each end. It deals with session and connection coordination.
Layer 4: The transport
layer...This
layer manages the end-to-end control (for example, determining whether all
packets have arrived) and error-checking. It ensures complete data transfer.
Layer 3: The network layer...This layer handles the
routing of the data (sending it in the right direction to the right destination
on outgoing transmissions and receiving incoming transmissions at the packet
level). The network layer does routing and forwarding.
Layer 2: The data-link
layer...This
layer provides synchronization for the physical level and does bit-stuffing for
strings of 1's in excess of 5. It furnishes transmission protocol knowledge and
management.
Layer 1: The physical
layer...This
layer conveys the bit stream through the network at the electrical and
mechanical level. It provides the hardware means of sending and receiving
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