Information Technology Reference
In-Depth Information
great deal of give and take, as we saw with the creation of an enhanced Cat 5e and
the installed-cable performance standards to support Gigabit Ethernet. 10 Gigabit
Ethernet over fiber needs to work well over existing media types, and it is critical
both to define an appropriate fiber-optic cable performance level and to create the
networking technology that will work over that fiber.
10 Gigabit Ethernet Fiber Standards.
There are three basic types of fiber-optic
cable in common LAN use. The three are 62.5 mm multimode, 50 mm multimode,
and 10 mm single-mode fiber-optic cables. In addition to these general classifica-
tions for fiber cable, there are also parameters, such as modal bandwidth, disper-
sion, and low-water-peak. These and other parameters act as “quality factors” in
differentiating between fiber-optic cables. It goes without saying, that only the very
highest quality fiber optic cables can support 10 Gb operation.
In the IEEE standard, the basic term for 10 Gigabit Ethernet is “10GBase,”
where the 10G stands for 10 gigabits per second, and the Base means baseband
operation (as opposed to signaling on a carrier, as with a cable-TV signal). The suf-
fix to 10GBase tells you the media (in our case the fiber type and signaling wave-
length), and the coding method. The complete descriptor has at least two, and
sometimes three elements.
Fiber media type suffixes are easy. L means long-wavelength, generally 1310
nm. S means short-wavelength, 850 nm. E means extended-wavelength, 1550 nm.
So, we have 10GbaseS_, 10GbaseL_, and 10GbaseE_, where the “_” represents
another element in the suffix.
Now, the coding method is essentially the same as for Fast Ethernet, although
the suffix letter designations are a little more arbitrary. X means the 8B/10B data
code and is the same coding used in many other technologies, including Fibre
Channel, as described early in the chapter. R means that a 64B/66B coding method
is used. W corresponds to the WAN Interface Specification (WIS) and it uses a spe-
cial format similar to SONET STS-192c (see OC-192 in Table 12.4). This is the sec-
ond letter of the suffix, so it gives us 10Gbase_X, 10Gbase_R, and 10Gbase_W.
So, when you put it all together, you get Physical layer standards such as
10GbaseSR and 10GbaseLR. The last element is optional, and normally used to
indicate a special mode of operation. Thus, 10GbaseLX4 is a long-wave fiber-optic
standard, using X (ANSI X3.230) coding, but split over four wavelengths. Some
combinations are not practical because of bandwidths, reach, and other constraints.
Now you know the rest of the story. Table 12.9 is a sanity-check.
10GBaseLX4 is the jewel of the group, as you can see from the table. By
employing a version of “coarse” wave-division multiplexing (WDM), LX4 handles
virtually all types of installed LAN fiber. It can use both common types of multi-
