| I was afraid my note might be misunderstood...
The point I was talking about is NOT dual homing. Dual homing means connecting
A and B both to M ports of concentrators, AND having one of those be a "standby"
(or "backup") connection. So at any one time you're only connected to a single
ring. If your A and B connections go to different concentrators, which are
connected to different rings, then you're still connected only to one ring
at a time, but as connections fail you are switched to another ring.
The case I mentioned earlier is a concentrator that has multiple data paths
inside. In such a concentrator, it would be possible to have A and B connected,
and have BOTH active, each connected to a separate internal data path. Some
people think this is useful. My opinion is that it is not, except as a way
for marketing people to confuse customers, make them spend more money, and
tie them to one or two vendors of expensive FDDI products.
The FDDI standard contains a LARGE number of options, some useful, many
useless. Each vendor implements only a subset of these options; which subset
depends on the vendor. All these (assuming you pay attention) conform to
the standard, and all should interoperate. The reason there are so many options
is that's how large standards committees operate, especially when some of the
loudest members are consultants whose income increases the more complexity
they help create!
paul
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