The CLVL abstraction provides the bundle an available bandwidth, ,
which varies with time and guarantees the entire bundle a target
loss rate,
. If the traffic arrival rate of the bundle is larger
than
, the extra traffic is dropped at the entry overlay node. The
overlay node can employ any QoS scheduling discipline to distribute
and the losses across the flows in the bundle. In particular, in a
Diffserv-like model, if every packet is associated with a priority, then
the overlay node can use these priorities to preferentially drop
packets and allocate bandwidth to different flows.
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While in general the available bandwidth, , of a CLVL bundle varies
with time, it might be possible to statistically bound the minimum
bandwidth of the bundle to offer bandwidth guarantees to a fraction of
OverQoS traffic. Given a small probability value,
, one can
capture the variations of the available bandwidth on a CLVL using a
distribution and determine a value
such that the
probability,
where
represents the probability
of not meeting the bandwidth guarantee,
. If the
corresponding
is a significant fraction of
, then OverQoS
can provide statistical bandwidth guarantees by allocating bandwidth
to flows within a CLVL as long as the total allocated bandwidth is
less than
. Table 1 tabulates all the
variables we use in expressing the properties of a CLVL.
In practice, we notice that the value of across overlay
links can be reasonably high implying that OverQoS can indeed be used
to provide meaningful statistical bandwidth guarantees to
applications. Figure 2 shows the distribution of
for three different overlay links traversing international links and
broadband networks: Lulea (Sweden)-Korea, Mazu (Boston)- Cable Modem
(SF), Netherlands-Intel (SF). The values of
across these
links to provide a
guarantee are 160 Kbps, 420 Kbps, and
269 Kbps respectively. Statistical bandwidth guarantees can be
provided only to a subset of the OverQoS flows, potentially at the
expense of other flows. Flows requiring guarantees should be given a
higher priority over other flows at an OverQoS node. The remaining
bandwidth
is distributed among the other flows.