TOKEN RING FIBER EXTENDERS
12
Whilst the mode of phantom current operation is explicitly defined for the lobe there is
no standard for phantom current use in trunk applications. However some form of
phantom mechanism has been widely adopted by many manufacturers who are keen
to increase main path integrity. As most of these have different mechanisms of
phantom generation/detect, interoperation between different vendors’ smart Ring In
and Ring Out ports is usually only possible with the smart mode (phantom current
mode) disabled.
The rule of thumb is “Lobe Connections are standard”: always use phantom current
(referred to as ACL on the LCL112A-TR). Trunk Connections do not use phantom
current in a standard way and do not use phantom current on the Ring In /Ring Out
path.
3.1.2
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Frequency Lockout
Frequency lockout mechanisms are designed to stop devices at 4Mbps crashing
16Mbps rings and vice versa. The lobe port of the MAU detects whether the data
received on its port is running at the correct speed. If the data is not at the correct
speed, or is not present, then the port is disabled.
This is important when establishing a link using LCL112A-TRs between say 2 lobe
ports as no data can be present on the link until AFTER THE LINK IS ESTABLISHED.
This can result in a “Catch 22” when the link will not insert until data is present, but no
data is present until the link is inserted.
The user should be aware that this does not apply to standard lobe style links between
a station and a concentrator.
3.1.3
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LCL112A-TR Trunk Operation
When the LCL112A-TR is set to trunk mode it creates a fiber backbone between the
two LCL112A-TRs that the other devices can connect to. When the backbone
between the LCL112A-TRs is first started it has no data present. This will stop the
LCL112A-TRs inserting into the lobe ports of active MAUs until an active station is
present on the ring.
Note: Whenever the LCL112A-TRs are set to trunk mode, links to active concentrator
ports will only insert if the far end device connects to a main ring or a station port and
that device is carrying valid data.
Trunk links between the active ports of two active MAUs may never insert as both
ports wait for the far end to send valid data. The application shown in Figure 4,
Concentrator Port to Concentrator Port, should be limited to passive MAUs or other
MAUs without frequency lockout.
