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Unformatted text preview: queuep;
if prob 0
p:label = ; = relabel p =
estimate p; dropped
b
estimate rateA; p; = est. arrival rate use Eq. 5 =
if dropped == FALSE
b
estimate rateF ; p; = est. accepted tra c rate =
b C
if A
if congested == FALSE
congested = TRUE ;
start time = crt time;
else
if crt time start time + Kc
b
b = b C=F ;
start time = crt time;
b
else = A C =
if congested == TRUE
congested = FALSE ;
start time = crt time;
tmp = 0; = use to compute new =
else
if crt time start time + Kc
tmp =maxtmp ; p:label;
else
b = tmp ;
start time = crt time;
tmp = 0; return b; Figure 2: The pseudocode of CSFQ.
time the bu er over ows, b is decreased by a small xed percentage taken to be 1 in our simulations. Moreover, to
avoid overcorrection, we make sure that during consecutive
updates b does not decrease by more than 25.
In addition, since there is little reason to consider a link
congested if the bu er is almost empty, we apply the following rule. If the link becomes uncongested by the test in
Figure 2, then we assume that it remains uncongested as
long as the bu er occupancy is less than some prede ned
threshold. In this paper we use a threshold that is half of
the total bu er capacity.
2.2.3 Label Rewriting
Our rate estimation algorithm in Section 2.2.1 allows us to
label packets with their ow's rate as they enter the island.
Our packet dropping algorithm described in Section 2.2.2
allows us to limit ows to their fair share of the bandwidth.
After a ow experiences signi cant losses at a congested link inside the island, however, the packet labels are no longer
an accurate estimate of its rate. We cannot rerun our estimation algorithm, because it involves per ow state. Fortunately, as note in Section 2.1 the outgoing rate is merely
the minimum between the incoming rate and the fair rate
. Therefore, we rewrite the the packet label L as Lnew = minLold ; ; 7
By doing so, the outgoing ow rates will be properly represented by the packet lab...
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This document was uploaded on 03/04/2014 for the course ENG 531 at Rice.
 Fall '10
 Eugene Ng

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