REQUIREMENTS/SPECIFICATIONS
Page 2-2
Lobe Cabling - In addition to IBM Type 3 unshielded twisted pair
(UTP), the TRMIM-20R supports voice grade UTP cable as described
in EIA Standard Proposal No. 1907-A. Table 2-1 lists IBM cable
types.
2.1.2 Cable Lengths
The TRMIM-20R is a passive concentrator. It neither regenerates
nor retimes ring signals and the cable lengths used with the
concentrator must consider the Adjusted Ring Length (ARL). ARL
results from recovery processes that attempt to restore continuity to a
broken ring. The ARL is the longest potential ring length, the ring
that would exist following recovery from a failure of the shortest ring
segment trunk cable. Refer to the discussion of token ring concepts
related to ARL in Appendix A. Appendix C describes how to calculate
cable lengths in your network, giving consideration to ARL.
Considering ARL, two cable lengths must be defined: Lobe Length
and Trunk Length. Their combined length defines the path
between two token ring stations and cannot exceed the maximum
drive distance.
Lobe Length - This is the physical length of UTP cable connecting a
station to the trunk coupling unit (TCU) port on the TRMIM-20R.
The recommended maximum length for the longest UTP lobe cable is
shown in Table 2-2. This is a recommended maximum because
cable length calculations for passive ring connections described in
Appendix C could produce a maximum lobe length for your network
that exceeds this limit. However, installing a lobe that exceeds the
recommended maximum should be avoided since it could restrict
future expansion of the network.
Trunk Length - This is the physical length of the STP cabling in the
main ring path, from Ring-Out to Ring-In on each of the attached
token ring devices. The cable budget for the trunk cabling must be
determined by performing the calculations described in Appendix C.
In a totally passive ring (no repeaters or active concentrators, etc. on
the ring), the entire trunk length must be included in calculation of
cable lengths. When only a portion of the ring is passive, the
combined length of the trunk cabling between the passive components
must be considered in the cable length calculations.