D-Link DES-3250TG User Manual page 58

DES-3250TG Layer 2 Fast Ethernet Switch User's Guide
proprietary, but communication between peers on the same
OSI layer is open and consistent.
A brief description of the most commonly used functional
layers is helpful to understand the scope of how protocol
layering works.
Layer 1
This is referred to as the physical layer. It handles the electrical
connections and signaling required to make a physical link
from one point in the network to another. It is on this layer that
the unique Media Access Control (MAC) address is defined.
Layer 2
This layer, commonly called the switching layer, allows end
station addressing and the establishment of connections
between them.
Layer 2 switching forwards packets based on the unique MAC
address of each end station and offers high-performance,
dedicated-bandwidth of Fast or Gigabit Ethernet within the
network.
Layer 2 does not ordinarily extend beyond the intranet. To
connect to the Internet usually requires a router and a modem
or other device to connect to an Internet Service Provider's
WAN. These are Layer 3 functions.
Layer 3
Commonly referred to as the routing layer, this layer provides
logical partitioning of networks (subnetting), scalability,
security, and Quality of Service (QoS).
50