Traffic Management for the Available Bit Rate (ABR) Service in ...

eld in the RM-cells (in the forward and/or backward directions). This
dissertation deals mainly with explicit rate feedback from switches.
VS/VD Control: In this mode, the switch may segment the ABR control
loop by appearing as a \virtual source" to one side of the loop and as a
\virtual destination" to the other side. We study the implications of this
mechanism on the ABR service later in this dissertation.
Switch Rule 2: This rule speci es how a switch may generate an RM cell in
case it is heavily congested and doesn't see RM cells from the source. Basically,
the rule allows such RM cells to only decrease the source rate, and these RM
cells are sent out-of-rate. This rule contains aspects of the Backward Explicit
Congestion Noti cation proposal [69] and the OSU scheme proposal described
later in this dissertation.
Switch Rule 3: This rule says that the RM cells may be transmitted out-of-
sequence, but the sequence integrity must be maintained. This rule allows the
switch the exibility to put the RM cells on a priority queue for faster feedback
to sources when congested. However, by queuing RM cells separately from the
data stream, the correlation between the quantities declared RM cells and the
actual values in the data stream may be lost.
Switch Rule 4 and 5: Rule 4 speci es alignment with ITU-T's I.371 draft,
and ensures the integrity of the MCR eld in the RM cell. Rule 5 allows the
optional implementation of a use-it-or-lose-it policy at the switch. We treat the
use-it-or-lose-it issue in greater detail later in this dissertation.
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