According to the ITU-T Recommendation 1.371 [3], there are
two categories of control mechanism for ATM networks: preventive
and reactive controls. Preventive control is open-loop,
meaning the control algorithm makes decision based on its local
node, such as link capacity and buffer availability in the system.
Reactive control is close-loop in which network situations are
feedback from the network to the sources.
CAC is an example of preven tive control. Its main role is to
determine whether a new connection request should be accepted
or rejected. The decision is based on the availability of resources
(bandwidth and buffer) and whether the OoS can be guaranteed
for a new connection without degrading the promiserl OoS of ex-.
isting connections. Conventional CAC relies on analytica[ models
in which parameters are based on a priori or user-specified
traffic descriptors [4] [5] [6]. However an analytical model may
not be able to capture the statistical nature of traffie sources.
This is because VBR traffic characteristics such as Sustainable
Cell Rate (SCR), Intrinsic Burst Tolerance (IBT) and Cell Delay
Variation (COY) are difficult for users to specify precisely. Improper
specification of traffic characteristics could lead to either
degraded OoS or link under-utilization.
Explicit rate (ER) switch algorithm for congestion control is
an example of reactive control. II uses ER field of the ReSOUTce
Management (RM) cells to convey network information
to sources. The main challenge of a feedback control is long
propagation delay which can cause buffer overflown and QoS
degradation. High utilization, low queueing delay and fairness
are thc main goals of a switch scheme. Switch algorithms use
either static threshold values [7] [8] or complex mathematical
expressions [9] for congestion control have an inherent disadvantage.
They cannot adapt well to traffic fluctuations, resulting
in high cell loss or low link utilization in some situations.
This paper proposes two traffic controllers based on fuzzy
logic prediction. Firstly, based on the concepts of free band-