D-Link DES-3326 User Manual - Layer 7
DES-3326 Layer 3 Fast Ethernet Switch User’s Guide
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Switch Management and Operating Concepts
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.
TCP/IP is a layered set of protocols. An example, such as sending
e-mail, can illustrate this. There is first a protocol for sending and
receiving e-mail. This protocol defines a set of commands to
identify the sender, the recipient, and the content of the e-mail.
The e-mail protocol will not handle the actual communication
between the two computers, this is done by TCP/IP. TCP/IP
handles the actual sending and receiving of the packets that make
up the e-mail exchange.