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The original IBM Cabling System specification released in 1984 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 pairs are enclosed in 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, if not equivalent, 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.
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The following table lists all the cable types defined by the IBM Cabling System specifications:
| IBM Type |
Cable Description | Impedance | Max Frequency |
IBM Specification |
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|---|---|---|---|---|---|
| 1 | Two shielded twisted pairs, 22 AWG solid copper conductors | 150 ohms | 16 MHz | Non-Plenum Data | 4716748 |
| Plenum Data | 4716749 | ||||
| Outdoor Data | 4716734 | ||||
| Riser | 6339585 | ||||
| 2 | Two shielded twisted pairs, 22 AWG solid copper conductors, plus Four voice grade twisted pairs, 22 AWG solid copper conductors | 150 ohms (data), 600 ohms (voice) |
16 MHz (data) |
Non-Plenum Data & Telephone | 4716739 |
| Plenum Data & Telephone | 4716738 | ||||
| 3 | Multipair 22 or 24 AWG Twisted Pair | 100 ohms | 16 MHz | Data or Telephone | |
| 5 | Two 100/140 µm Fibers | Fiber Optic | 4716744 | ||
| 5J | Two 50/125 µm Fibers | Fiber Optic | 6339090 | ||
| 6 | Two shielded twisted pairs, 26 AWG stranded copper conductors | 150 ohms | 16 MHz | Patch Panel Data | 4716743 |
| 8 | Two individually shielded flat parallel pairs, 26 AWG solid copper conductors | 150 ohms | 16 MHz | Under Carpet Data | 4716750 |
| 9 | Two shielded twisted pairs, 26 AWG solid or stranded copper conductors | 150 ohms | 16 MHz | Non-Plenum Data | 74F8680 |
| Plenum Data | 6339583 | ||||
| Riser | 74F9730 | ||||
| 1A | Two shielded twisted pairs, 22 AWG solid copper conductors | 150 ohms | 300 MHz | Non-Plenum Data | 33G2772 |
| Plenum Data | 33G8220 | ||||
| Riser | 33G2774 | ||||
| 2A | Two shielded twisted pairs, 22 AWG solid copper conductors, plus Four voice grade twisted pairs, 22 AWG solid copper conductors | 150 ohms (data), 600 ohms (voice) |
300 MHz (data) |
Non-Plenum Data & Telephone | 33G2773 |
| Plenum Data & Telephone | 33G8221 | ||||
| 6A | Two shielded twisted pairs, 26 AWG stranded copper conductors | 150 ohms | 300 MHz | Patch Panel Data | 33G2775 |
| 9A | Two shielded twisted pairs, 26 AWG solid or stranded copper conductors | 150 ohms | 300 MHz | Non-Plenum Data | 33G8224 |
| Plenum Data | 33G8223 | ||||
| Riser | 33G2776 | ||||
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