Cabletron Systems 100BASE-FX, Cabling Manual

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Token Ring Network Requirements
10-2 IEEE 802.5 Shielded Twisted Pair
Attenuation
The attenuation limit for any Token Ring STP cable link is dependent upon the
operating speed of the Token Ring network. Token Ring networks that operate at
a 16 Mbps speed (16 MHz) have slightly different cabling requirements than those
Token Ring networks operating at 4 Mbps (4 MHz).
Attenuation, when calculated, must take all cabling devices in the cable path into
account. A typical attenuation test must include the jumper cabling used at the
station and at the wiring closet, and any patch panels, punchdown blocks, and
wallplates in the installation.
STP Type 1,2
Acceptable levels of attenuation for STP cables of Types 1 and 2 are not dependent
upon the circuitry type being used by the Token Ring networking hardware. The
attenuation limit for Type 1 or Type 2 STP at 4 MHz is 22 dB/km or less. If the
speed of the Token Ring network is 16 Mbps, the attenuation limit is 45 dB/km or
less.
STP Type 6,9
The attenuation limits for Type 6 and Type 9 STP cabling are slightly higher for
each speed class. Networks operating at 4 MHz may use cabling with an
attenuation of less than 33 dB/km, while 16 MHz networks may use cabling with
attenuation levels below 66 dB/km.
Impedance
All STP cable used in a Token Ring installation must have an impedance rating
between 127.5
Ω
and 172.5
Ω
. STP cables of any type that are not within this
impedance window may not function properly with the Token Ring hardware,
causing poor network performance or error conditions.