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16
IBM 8265: Planning and Site Preparation Guide
For installations where cable cross section or cable cost considerations prohibit the
use of standard 150-ohm STP-A cable, and where cabling distances do not exceed
60 m (197 ft), use of thin STP or Type 9 cable is appropriate. This cable is similar to
standard STP-A with the important exception that its attenuation is higher. However,
applications that can be run on 90-meter lengths of standard STP-A cable will perform
adequately on up to 60 meters of thin STP or Type 9 cable.
Where copper cable other than 150-ohm STP is desired, 4-pair Category 5 cable
should be used for high-speed data transmission applications. In the U.S.A. and
Canada, the only approved copper choice other than 150-ohm STP is 4 pair 100-ohm
cable. Elsewhere, both 100- and 120-ohm copper cabling types are allowed. Since
many LAN and high speed data transmission standards, both existing and in
development, support 100-ohm and not 120-ohm cable, a decision to use 120-ohm
cabling should be made with caution.
•
Use of Category 3 UTP in new installations is strongly discouraged for any high-
speed data applications. The tiny cost savings associated with this cable do not
adequately compensate for the increased system performance risk from external
noise sources, increased crosstalk, and increased cable attenuation compared
with the Category 5 UTP choices. In addition, Category 3 cabling may limit
allowable configurations. For example, for 16Mbps token-ring, Category 3 cabling
will not support 90 meter horizontal cabling runs using passive hubs.
•
If shielded 100- or 120-ohm cable is used, care should be taken to guarantee rf
shield continuity from the attaching products in the telecommunications closet to
the attaching office product. Since there are presently no standards for shielded
modular connectors, you will have to rely on manufacturers and installers
guarantees, or on independent testing.
•
Although 2-pair 100- and 120-ohm cable is allowed by DIS 11801, its use is
discouraged. Note that the use of 2-pair 100-ohm cable for token ring, Ethernet,
and FDDI, each requires different pair selections. Therefore, no 2-pair selection
can be considered generic. Costly pair rearrangement would be necessary to
support the different applications.
•
IBM supports the standard multimode optical fiber cable and connectors for
horizontal attachment. Although optical fiber may be the appropriate choice for
specific applications, its use as the primary data cable for general application from
telecommunications closet to office is discouraged since it may significantly limit
the choice of economical attachments.
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