observation of traffic behaviour. This approach is
useful to take into account aggregate bandwidth
fluctuations by repeated “on-the-fly” measurements
in past periodic time intervals, and subsequent actual
bandwidth estimation, even if this generally comes
at a cost of a computation complexity overload. This
approach is particularly suitable in an on-line
context, where only part of the aggregate data set is
available for bandwidth estimation and actual load
prediction.
An efficient MBAC scheme should thus provide
an intelligent admission decision, based on network
resource measurements, whose accuracy strongly
affect MBAC efficiency and robustness. MBAC
algorithms exploiting past traffic measurements and
QoS parameters a priori specified decide, based on
actual traffic estimation, the new flow admission or
rejection.
Several different strategies for traffic
measurements have been developed, each of them
strongly influencing the MBAC algorithm
performance. In Jamin et al (1997a) three different
MBAC techniques are compared. In Jamin et al
(1997b) a MBAC algorithm is proposed for a packet
delivery service with bounded delay requirements.
In this algorithm, admission decision is based on a
token bucket filter model, that is able to calculate
worst case delays. The algorithm has been tested in a
wide variety of scenarios, and including also LRD
traffic. The MBAC proposed in Casetti et al (1996)
presents a quite simple traffic estimation process in a
single-link scenario, able to achieve a high
bandwidth utilization, without violating, at the same
time, QoS guarantees, specified as delay bounds. In
Grossglauser and Tse (1999) the impact of some
parameters, like estimation errors, flow dynamics
(departures, arrivals, and bursty traffic time scales)
and system memory, on MBAC robustness are
analyzed. Their reciprocal interactions and impact
on QoS specifications are considered for a unified
framework. In Grossglauser and Tse (2003) a
MBAC algorithm is proposed, based on a time scale
decomposition of a flow aggregate, taking also into
account flow arrivals and/or departures. Bandwidth
fluctuations are decomposed into “fast time scale”
and “slow time scale” contributes, separated by the
“critical time scale” threshold. Aggregate
fluctuations slower than the critical time scale are
exploited for admission control policy while the
faster are used to estimate the necessary amount of
bandwidth needed to absorb high bandwidth
fluctuations in a brief time period.
In this paper a novel MBAC algorithm is
proposed. It is based on a set of aggregate traffic
measurements performed in past time intervals, to
derive statistically an estimation of the aggregate
bandwidth and of the available bandwidth margin,
necessary to absorb instantaneous peak rates, with
the same approach used in Grossglauser and Tse
(2003). Available bandwidth estimation is then
exploited to admit new flows without violating QoS
requirements of the whole aggregation.
The main novelty of the proposed algorithm lies
in the criterion adopted for aggregate bandwidth
estimation, that makes use of linear predictive
techniques. In particular, aggregate traffic
measurements are performed in time intervals
preceding the new flow request of admission. This
data set is exploited to statistically derive a
prediction of the aggregate behaviour in a future
time interval. This prediction is then combined with
the QoS parameter, that is, overflow probability, to
decide the new flow admission. In this context the
overflow probability is the probability that the whole
aggregate, included the new flow, exceeds the
available link bandwidth.
The linear prediction technique dynamically
performs an estimation of the statistical aggregate
characteristics; the algorithm utilized is based on a
“multi-channel” linear prediction, to determine the
predictable characteristics of a set N different
multiplexed video sources.
Predictive
bandwidth
estimation
subsystem
Measurement
Based
Admission
Control
subsystem
Figure 1: the processing scheme adopted in the MBAC
system.
As it will be more clear in the next sections, this
work aims at implementing a numeric filter that
properly describes the predictable portion of
aggregate traffic to quantify the overflow probability
for admission decision.
The paper is structured as follows. In Section 2,
the novel MBAC approach based on a bandwidth
prediction system, is presented and explained. In
Section 2.1 the predictive system is analyzed in
detail. Bandwidth prediction is then used in the
MBAC algorithm, whose principles are explained in
Section 2.2. In Section 2.3 the whole MBAC
algorithm is implemented. Section 3 provides some
significant numerical results. Finally, Section 4
gives some conclusions to the proposed work.
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