Information Technology Reference
In-Depth Information
efits of this approach go beyond the telecommunications issues. It is also a good idea
to provide an orderly system of cable ducts or sleeves, both for interfloor and fire-
wall use. Proper ducting will allow workers to place UL-rated firestopping material
in the ducts to enhance fire protection. Also, because many of the utility shafts are
closed and reinforced concrete structures, this avoids the problem of random wall
penetrations and “sneaker” cables that are forced alongside existing pipe and
HVAC penetrations.
Maximum Drop Length
LAN wiring standards dictate strict distance limits for horizontal cable runs. These
cable drop lengths include the entire cable from the point of termination in the
telecommunications room to the workstation outlet. Standards also cover the max-
imum distances between telecommunications rooms. In this way, the requirements
of TIA 568-C and 569-B work together, in balance with the building's architecture,
to achieve a compliant wiring system for your LAN that will meet your needed per-
formance.
The maximum length for a horizontal cable is 90 m (295 ft). This 90 m length
excludes the user cord that connects from the outlet to the user workstation (or tele-
phone instrument) and the patch cord (or jumper) that connects from the patch
panel (or cross-connect field) to a hub or other device. This is a maximum accept-
able length and not simply an average length or a goal. You should try to keep your
wiring well below this length in most cases. At least two telecommunications out-
lets must be provided for each individual work area.
Although some of the lower-speed LANs, such as 10BaseT and even Token-
Ring, may run to longer distances of as much as 150 m, exceeding the standard
intentionally is a bad idea. You cannot expect such run lengths to support 100/1000
Mbps data rates at all, and any equipment problems will be blamed on the exces-
sive drop lengths. As a matter of fact, cable testers are required to fail a basic link
longer than 90 m, allowing for test cables and measurement accuracy. For a com-
plete discussion of measuring cable lengths using cable testers, see Chapter 15.
The allowable backbone cable distances between telecommunications rooms
depend on the type of cable you use as well as practical considerations.
For example, the standard allows 2000 m (6560 ft) from TR to MC for fiber-
optic cable, but only 800 m (2624 ft) for unshielded twisted-pair cable. The dis-
tances are even less between ICs and the other two types of telecommunications
rooms. However, practice may dictate much smaller distances. If you wish to con-
nect between two telecommunications rooms on a 100BaseT or a gigabit link, for
example, you would have to limit the backbone run to the same 90 m you are lim-
