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destination. IP security allows for authentication and
encryption. IP not only allows for user-to-user
communication, but also for transmission from point-to-
multipoint (known as IP multicasting).
Layer 4
This layer, known as the transport layer, establishes the
communication path between user applications and the
network infrastructure and defines the method of
communicating. TCP and UDP are well-known protocols in
the transport layer. TCP is a "connection-oriented" protocol,
and requires the establishment of parameters for
transmission prior to the exchange of data. Web technology
is based on TCP. UDP is "connectionless" and requires no
connection setup. This is important for multicast traffic,
which cannot tolerate the overhead and latency of TCP.
TCP and UDP also differ in the amount of error recovery
provided and whether or not it is visible to the user
application. Both TCP and UDP are layered on IP, which
has minimal error recovery and detection. TCP forces
retransmission of data that was lost by the lower layers, UDP
does not.
Layer 7
This layer, known as the application layer, provides access
to either the end user application software such as a
database. Users communicate with the application, which in
turn delivers data to the transport layer. Applications do not
usually communicate directly with lower layers They are
written to use a specific communication library, like the
popular WinSock library.
Software developers must decide what type of transport
mechanism is necessary. For example, Web access
requires reliable, error-free access and would demand TCP,
Multimedia, on the other hand, requires low overhead and
latency and commonly uses UDP.
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