RE: [RPRWG] What rcvdFairRate should be used if SC-FCM are not being received?
> Regarding the initial value of rcvdFairRate, I do not
> understand all the
> math involved. My reasoning behind believing the downstream
> node must be
> congested by initializing rcvdFairRate to unreservedRate is that I
> understand rcvdFairRate != FULL_RATE to mean congestion. If you use
> unreservedRate (which != FULL_RATE), to me that indicates
> congestion. I
> suppose that is OK, since that stops a new node coming
> on-line on a busy
> ring and blasting the ring before it figures out a natural
> balance. I am
> happy to let people more knowledgeable than me decide this
> initial value.
Michael,
Your observation that rcvdFairRate != FULL_RATE means
congestion is correct. And that's what would have been
my knee-jerk reaction to the response from Necdet and KK.
However, on thinking things through, one can see
that if a node advertises unreservedRate, it would
mean that the only case that a node would advertise
unreservedRate would be if it is in the conservative
mode and if neither it is congested nor any other node
on the ring is congested. In the aggressive mode,
the only time a node advertises a non FULL_RATE value
is when all of the following are true:
- The node is congested, and
- There is a node upstream of it that may be the
cause of congestion.
The value advertised is the value of the "add rate".
If the node added unreservedRate worth of traffic,
obviously an upstream station cannot be the cause of
congestion. So this can never happen in a node that
is in aggressive mode.
Of course, unreservedRate at the nodes can be different
depending on whether they are single/dual transit buffer
nodes and the amount of sub class A0 bandwidth provisioned
so these values may be out of sync.
That said, I tend to agree with you that the initial
value should of the rcvdFairRate should be set to FULL_RATE
since it removes this ambiguity. The initial value
of the allowedRate and allowedRateCongested should
be unreservedRate. And the initial value of the
TTLtoCongestion should be MAX_STATIONS.
-Anoop