Recovering packets creates
excessive overhead that reduces performance.
To accommodate this type of traf?¬?c, TCP architects redesigned the protocol suite to include
UDP. The basic addressing and packet-forwarding service in the network layer was IP. TCP
and UDP are in the transport layer on top of IP, and both use IP services.
UDP offers only minimal, nonguaranteed transport services and gives applications direct
access to the IP layer. UDP is used by applications that do not require the level of service
of TCP or that want to use communications services such as multicast or broadcast delivery,
not available from TCP.
An analogy of the UDP protocol services would be using the postal service to send ?¬‚iers
notifying all of your neighbors of your garage sale. In this example, you make a ?¬‚ier
advertising the day, time, and location of your garage sale. You address each ?¬‚ier with the
speci?¬?c name and address of each neighbor within a 2-mile radius of your house. The postal
service delivers each ?¬‚ier by any truck and any route. However, it is not important if a ?¬‚ier
is lost in transit or if a neighbor acknowledges receipt of the ?¬‚ier.
Understanding TCP/IP??™s Transport and Application Layers 67
TCP/IP Applications
In addition to including the IP, TCP, and UDP protocols, the TCP/IP protocol suite also
includes applications that support other services such as ?¬?le transfer, e-mail, and remote
login.
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