| What are you asking? Here are some random thoughts....
If you have Raj Jain's article, then you have some imformation on how it works,
both in terms of the <knobs> and in terms of the <reality>. There are other
sources of information that provide more detail, for example the FDDI standard
itself. So, do you want to know how it works at the MAC layer?
Basically the way it works is that everyone is trying to maintain a token
rotation time, ie., the maximum time between the times that a station sees
two tokens (which means no data). The higher your priority, the less you care
about how long between the successive free tokens, the highest being that
you can grab every token. Lower priority stations can only grab a token
if by doing so they will not slow down the token rotation time below the
specified level.
The things that are unfair is that it isn't clear how you figure out how to
set each stations priority and satisfy what you think is fair. Another thing
is that it is possible to set the priorties to that under certain loads the
low priority stations get so little bandwidth that they can't operate.
Usually it is specific kinds of traffic that you want to give priority to,
not specific stations, and FDDI doesn't address that problem.
I think one of questions Raj Jain asked was, as a vendor, what priority do
you assign to stations under your control. If DEC, as good citizens selected
a medium priority, what would encourage Sun or IBM from setting theirs to
high to help their network products perform better than DEC's?
Or are you asking how you set the knobs on DEC gear?
Or are you asking what management tools are available to set and manage the
knobs? For DEC gear? For all vendor's gear?
It is part of the FDDI standard as approved. The allocation to each station
depends on the priorities of all the other stations. This means you don't
really know how much you'll get, just by setting the priority, and more
important, you don't exactly when you will get it. FDDI-II is adding
what amounts to static allocation of bandwidth by means of time division
multiplexing, so you will be sure of getting a certain amount of bandwidth
at fixed time intervals. But this is different than priorities.
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| Hallo,
I want to know how it works at the MAC layer and specially what
management tools are available to set and manage the knobs for all
vendors gear. Did I understand you in the right way, that you haven't
got the possibility to manage the priority of the complete ring? So
that you never know what really hapens if you chance the priority of a
few stations?
Wiltrud
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