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

which shares the link equally as all other connections. The link allocates rates fairly
among all sources including the phantom.
Speci cally, the variable is de ned to be the unused link capacity, i.e.,
Link Capacity ;
(Rates of sessions that use the link).
It is measured as:
(Numberofcellstransmittableonlink ; Numberofcellsinput)=
where is a xed time interval.
Observe that can be greater than zero, when the actual queue at the link is
non-zero.
The rate of sessions that are above are reduced towards and the rate of
sessions that are below may be increased. The mechanism reaches a steady state
only when the unused capacity ( ) is equal to the maximum rate of any session that
crosses the link and all the sessions that are constrained by the link are at this rate.
So, is the \fairshare" value at each link.
For example [3], if three sessions share a 100 Mbps link, then in the steady state,
each session receives 25 Mbps and the link utilization is 75 % ( = 25Mbps). How-
ever, if two of the three sessions are restricted elsewhere to 10 Mbps each, the third
sessions gets 40 Mbps ( = 40Mbps).
The scheme addresses ve important implementation aspects:
1. Measuring : Naive measurement of can be very noisy. The scheme uses
exponential averaging to smooth out variance in and accumulates it in a
variable called \Maximum Allowed Cell Rate (MACR)":
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