TOKEN RING FIBER EXTENDERS
13
Full Duplex Operation
As stated above in trunk mode the LCL112A-TRs form a fiber backbone between the
two ends. This backbone does not carry any data until a device has inserted into the
ring. When switch ports connect to this ring it appears as the lobe port of a passive
MAU. No communication is possible between switch ports at either end of the link until
after insertion has taken place. This stops the auto-negotiation used to trade-up to full
duplex used by most switches.
To avoid this problem always connect switch ports together in lobe mode which
carries the data before the link is inserted using phantom current.
3.1.4
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LCL112A-TR Lobe Operation
Lobe applications are the most common application for the LCL112A-TR. Here
connection is always made from a station port to a lobe or concentrator port.
Examples of station ports are:
1)
!
Switch ports permanently configured as “NODE", “STATION” or “ADAPTER”.
2)
!
Standard Token Ring NICs
3)
!
Bridge or Router ports.
Examples of concentrator ports are:
1)
!
Switch ports configured as “Concentrator”, “Lobe” or “Port”.
2)
!
Standard Hub lobe ports
In lobe mode the communication path between the station and the concentrator
operates as if the station and concentrator were connected using a copper cable. This
allows the auto-negotiation (trade-up) mechanisms used by Token Ring switches
and frequency lockout mechanisms to operate correctly as the whole link can carry
data end to end before the device is inserted by phantom current into the ring.
3.1.5
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Pair Swapping during Auto-negotiation
Some NICs and switch ports that have full duplex capability not only negotiate speed
and mode of operation but local pair configuration too.
One device opts to be the station, the other the concentrator. This can involve the
switch swapping the transmit and receive pairs round after negotiation. As the
LCL112A-TR does not take part in the negotiation process it cannot perform pair
swapping in this way.
Consequently the ports of a switch must be fixed. One as a station and the other as a
concentrator and the local LCL112A-TRs configured to suit that fixed configuration.
