The OSI Layers
Background Information
The OSI architecture was set up by the ISO (International Standards
Organization) as the first formally defined way of connecting computers. The
OSI architecture divides network functionality up into seven layers, where
various protocols implement the functionality assigned to a given layer.
The Layers
The Physical Layer
This is the first layer of standards. It’s a set of rules regarding the hardware
used to transmit data. Among items covered at this layer are the voltages
used, the timings of transmission, and the rules used for the initial
handshaking connection.
The Data Link Layer
The physical layer provides the data link layer with bits. Now this layer
provides the bits with some meaning. We no longer deal with bits but
instead with data frames - packets, containing data as well as control
information. The data link layer adds flags to indicate the start and end of
messages.
This layer’s standards perform two important tasks. It ensures that data is
not mistaken for flags, and that it checks for errors within the frame.
The Network Layer
The network layer, is concerned with packet switching. It establishes virtual
circuits (Paths between terminals) for data communications. As the sending
end, the network layer repackages messages from the transport layer above
it into data packets, so the lower layers can transmit them.
The Transport Layer
The transport layer of the OSI model has many functions, including several
order f error recognitions and recoveries. As the highest order, the Transport
layer can detect errors, identify packets that have been sent in the incorrect
order, and then rearrange them. The transport layer also regulates the
information flow by controlling the messages movements.
