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DES-3326S Layer 3 Fast Ethernet Switch User’s Guide
Switch Management and Operating Concepts 95
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.
TCP/IP
The TCP/IP protocol suite is a set of protocols that allow
computers to share resources across a network. TCP and IP
are only two of the Internet suite of protocols, but they are the
best known and it has become common to refer the entire
family of Internet protocols as TCP/IP.