Specifications

RADring
Installation & Operation Manual Token Ring Desing Considerations
3/11/98 12:26 Simplified Design Rules 6-9
6.3 Maximum Number of Stations per Ring and the TJA
Module
A limiting factor in determining the maximum number of stations per ring is
the correlated jitter introduced into the token ring signal by active stations,
active lobes and long, low quality cables.
In order to overcome the inherent limitations in using active modules or
when using lower quality cables, the TJA ensures that the token ring signal is
cleared of jitter, thus ensuring increased station count under these
conditions.
TJA Unique
Benefits
Unlike an adapter card, the TJA is designed to correct frequency jitter. The
TJA dampens the frequency jitter of the incoming data, so that the TJA
output restores the pure frequency phase state created by the active
monitor. This means that if a TJA unit is inserted into every RADring hub,
the frequency jitter will never be enough to overrun the active monitor's
elastic buffer and cause soft errors. With the TJA in every RADring hub, the
number of users on the ring may increase to the original 250, irrespective of
media types and quality
TJA
Configuration
Since the active monitor can at any time be any adapter card on the ring (it
will tend to move around as users are inserted and removed), the use of
only one TJA is not recommended. For example, if the active monitor is the
adapter card directly preceding the TJA unit, the unit won't really be
cleaning up any jitter at all because the data will be clean at that point. So,
at least two units should be used, and they should be placed so that an
approximately equal number of users are between them. Table 6.3 defines
the frequency with which TJA should be used to achieve maximum station
count according to media and module type.
6.4 Simplified Design Rules
Just as no two organizations have exactly the same needs, no two networks
are created equal. For this reason, instead of providing strict rules for
implementation of Token Ring networks using RADring, the following
configurations should provide guidelines which will enable your organization
to utilize the benefits of Token Ring to their maximum.
The configuration should be used to provide guaranteed lobe distances and
station count irrespective of the topology of the ring and wiring closets, and
without the need to calculate the worst case ring length. The simplified
design rules can be divided into two parts:
1. Distance between hubs
2. Lobe distances