Installation
3-6
SmartLine 16 User’s Guide
Calculating When a Repeater Becomes
Necessary
In installations where you wish to install stacks of MAUs in more
than one wiring closet, the distance between stacks can cause a
reduction in the maximum length of lobe cabling specified in Table
3-1. This occurs when the token ring cable lengths exceed the drive
capability of the adapter cards in the workstations.
In a worst-case evaluation, a single workstation (the one with the
longest lobe cable) would have to keep the token in motion with all
but the shortest ring cable operating in loopback. These calculations
let you know when your cable lengths are too long for the worst case
condition. You can employ one or more repeaters to span the longest
distances when your cables are too long. Any MAU ring or lobe
interconnection made using a repeater plays no role in these
calculations. Proceed as follows:
1. Add up all the lengths of cables interconnecting MAUs. Ignore
the short cables (under eight feet) used to interconnect MAUs in
the same closet. Evaluate any MAUs separated by repeaters as if
they were on separate LAN systems.
2. Calculate the Adjusted Ring Length (ARL) by subtracting the
shortest cable distance from the total length. Figure 3-4 shows an
example that has 100-, 150-, and 50-foot lengths and an ARL of
250 feet.
3. Add the longest lobe cable length to the ARL found in step 2.
Ignore the lobe connections that employ repeaters.
4. In Table 3-2 or 3-3, find the number listed for your setup. Note
that the distances represent maximums that vary according to the
number of MAUs, the number of closets, the type of cable used,
and the ring speed in use.
5. Compare your step 3 results with the number found for your
setup in step 4. If the number calculated in step 3 exceeds the
value found in the table, and you have no options for
reducing cable length, you must install one or more repeaters.
After employing a repeater, repeat these steps for the new setup.
