The Variety of Ethernet Physical Layer Standards
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The term Ethernet refers to an entire family of standards. Some standards define the specifics
of how to send data over a particular type of cabling, and at a particular speed. Other
standards define protocols, or rules, that the Ethernet nodes must follow to be a part of an
Ethernet LAN. All these Ethernet standards come from the IEEE and include the number
802.3 as the beginning part of the standard name.
Ethernet supports a large variety of options for physical Ethernet links given its long history
over the last 40 or so years. Today, Ethernet includes many standards for different kinds of
optical and copper cabling, and for speeds from 10 megabits per second (Mbps) up to 100
gigabits per second (Gbps). The standards also differ as far as the types of cabling and the
allowed length of the cabling.
The most fundamental cabling choice has to do with the materials used inside the cable for
the physical transmission of bits: either copper wires or glass fibers. The use of unshielded
twisted-pair (UTP) cabling saves money compared to optical fibers, with Ethernet nodes
using the wires inside the cable to send data over electrical circuits. Fiber-optic cabling,
the more expensive alternative, allows Ethernet nodes to send light over glass fibers in the
center of the cable. Although more expensive, optical cables typically allow longer cabling
distances between nodes.
To be ready to choose the products to purchase for a new Ethernet LAN, a network engineer
must know the names and features of the different Ethernet standards supported in
Ethernet products. The IEEE defines Ethernet physical layer standards using a couple of
naming conventions. The formal name begins with 802.3 followed by some suffix letters.
The IEEE also uses more meaningful shortcut names that identify the speed, as well as a
clue about whether the cabling is UTP (with a suffix that includes T) or fiber (with a suffix
that includes X).
Table 2-2 lists a few Ethernet physical layer standards. First, the table lists enough names
so that you get a sense of the IEEE naming conventions. It also lists the four most common
standards that use UTP cabling, because this book’s discussion of Ethernet focuses mainly
on the UTP options.
Table 2-2 Examples of Types of Ethernet
NOTE Fiber-optic cabling contains long thin strands of fiberglass. The attached Ethernet
nodes send light over the glass fiber in the cable, encoding the bits as changes in the light.