Learning by Doing: CISCO Certified Network ... - SCN Research

Session
Transport
Network
Data Link
Physical
synchronizes dialogue between
presentation layer entities and
manages their data exchange.
Information is encapsulated
into data blocks here.
Responsible for reliable
network communication
between end nodes and
provides transport mechanisms
for the est., maintenance, and
termination of virtual circuits,
transport fault detection and
recovery and information flow
control.
Provides connectivity and path
selection between two end
systems where routing occurs.
Segments are encapsulated into
packets here.
Concerned with physical
addressing, network topology,
and media access. Packets are
encapsulated into frames here.
Describes the various types of
networking media. Frames are
converted into bits here.
Defines the electrical and
functional specifications for
activating and maintaining the
link between end systems.
Let’s compare. My definitions of the OSI model layers are:
Application—Where most non-networking programs function. This is the layer where
networking (like client-server) and the encapsulation process starts and ends.
Presentation—The second step in networking. This is where data is compressed,
formatted or encrypted. The “super-secret-spy-stuff” layer.
Session—This is where networking “sessions” between two devices are started, managed,
and terminated. The information is called “data.”
Transport—This is where the data is “chunked” into “segments” before being passed to
the network layer. Each chunk/segment is labeled 1 of X, 2 of X, 3 of X, etc. This is the
layer predominantly in charge of error control, even though each individual layer has its
own error control (to a lesser extent).
Network—This is where each segment is given directions on how to get from here to
there using logical addresses. After this information is added the segment is called a
“packet.”
68