D-Link DES-3250TG User Manual page 59

DES-3250TG Layer 2 Fast Ethernet Switch User's Guide
The backbone of the Internet is built using Layer 3 functions.
IP is the premier Layer 3 protocol.
IP is itself, only one protocol in the IP protocol suite. More
extensive capabilities are found in the other protocols of the IP
suite. For example, the Domain Name System (DNS) associates
IP addresses with text names, the Dynamic Host Configuration
Protocol (DCHP) eases the administration of IP addresses, and
routing protocols such as the Routing Information Protocol
(RIP), the Open Shortest Path First (OSPF), and the Border
Gateway Protocol (BGP) enable Layer 3 devices to direct data
traffic to the intended 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.
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