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Q27: What is IBM Cabling System?
A27:The original IBM Cabling System specification defined the 150 ohm
STP cable Types 1, 2, 6, 8, & 9 for support of frequencies up to 16
MHz.It also defined the 100 ohm Type 3 UTP cable, and Type 5 & 5J
fiber optic cables. Later, an enhanced IBM Cabling System defined STP-A
cable Types 1A, 2A, 6A, & 9A for support of FDDI and frequencies up
to 300 MHz. The "A" suffix denotes the enhanced IBM Cabling
System. The original IBM Cabling System was defined in IBM publication
GA27-3773. The enhanced, or STP-A, cabling is defined in the TIA/EIA 568-A
standard.
Generically, the term "shielded twisted pair" can be used to
refer to any twisted pair cabling in which the overall cables are screened
with an outer shield. Individual pairs may also be shielded. However,
the acronym "STP" most often refers to the 150 ohm shielded
twisted pair cables defined by the IBM Cabling System specifications and
used with Token-Ring networks. 150 ohm STP should not be confused with
the 100 ohm shielded twisted pair used with Ethernet networks commonly
known as "screened twisted pair" (ScTP) or "foil twisted
pair" (FTP).
Type 1 (1A) STP is the stiff black cable most commonly associated with
the IBM Cabling System. It contains two "data grade" shielded
twisted pairs. Type 2 (2A) STP is the same as Type 1 (1A) except that
it also contains four "voice grade" twisted pairs. The two data
grade pairs are intended for data networking such as Token-Ring, while
the four voice grade pairs are intended for telephone connections. Type
2 (2A) STP allows a single cable to be routed to each office that supports
both data and voice connections.Types 6 (6A) & 9 (9A) STP contain
two shielded twisted pairs that are constructed of a smaller wire gage
that makes them better suited for applications where a flexible cable
is required. Type 6 (6A) is typically used for short patch cables. Type
9 (9A) is typically used to connect between a station adapter and a wall
outlet. Type 8 cabling consists of two individually shielded flat parallel
pairs.The wires pairs are flat instead of twisted which reduces the thickness
of the cable. This makes Type 8 ideal for an office environment where
the cabling has to be routed under carpet.
IBM Type 3 cabling is similar to the Category 3 "unshielded twisted
pair" (UTP) cabling typically used with Ethernet 10Base-T. It has
a 100 ohm impedance in contrast to the 150 ohm impedance of STP cabling.
It usually includes four twisted pairs as opposed to STP cabling which
has only two twisted pairs.
The following table lists all the cable types defined by the IBM Cabling
System specifications.
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