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Data Link Layer (Layer 2)
(Page 2 of 2)
Physical Layer Requirements Definition and Network Interconnection Device Layers
As I mentioned in the
topic discussing the physical layer, that
layer and the data link layer are very closely related. The requirements
for the physical layer of a network are often part of the data link
layer definition of a particular technology. Certain physical layer
hardware and encoding aspects are specified by the DLL technology being
used. The best example of this is the Ethernet standard, IEEE 802.3,
which specifies not just how Ethernet works at the data link layer,
but also its various physical layers.
Since the data link layer and physical
layer are so closely related, many types of hardware are associated
with the data link layer. Network interface cards (NICs) typically implement
a specific data link layer technology, so they are often called Ethernet
cards, Token Ring cards, and so on. There are also
a number of network interconnection devices that are said to operate
at layer 2, in whole or in part, because they make decisions about
what to do with data they receive by looking at data link layer frames.
These devices include most bridges, switches and barters, though the
latter two also encompass functions performed by layer three.
Some of the most popular technologies
and protocols generally associated with layer 2 are Ethernet, Token
Ring, FDDI (plus CDDI), HomePNA, IEEE 802.11, ATM, and TCP/IP's Serial
Link Interface Protocol (SLIP) and Point-To-Point Protocol (PPP).
Key Concept: The second OSI Reference Model layer is the data link layer. This is the place where most LAN and wireless LAN technologies are defined. Layer two is responsible for logical link control, media access control, hardware addressing, error detection and handling, and defining physical layer standards. It is often divided into the logical link control (LLC) and media access control (MAC) sublayers, based on the IEEE 802 Project that uses that architecture.
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Version 3.0 - Version Date: September 20, 2005
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