The purposes of Layer 2 devices in the
network are to provide flow control, error detection and correction,
and to reduce congestion in the network.
The two most common Layer 2 devices (other than the
NIC, which every host on the network has to have) are bridges and LAN
switches. This section will concentrate on the implementation of LAN
switching at Layer 2. 
Collisions and collision domain size
are two factors that will negatively affect the performance of a
network. By using LAN switching we can create microsegmentation of the
network thus effectively eliminating collisions and reducing the size
of collision domains. Another important characteristic of the LAN
switch is how it can allocate bandwidth on a per port basis thus
allowing more bandwidth to vertical cabling, uplinks and servers. 
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