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necessary refinements for the seminal Packet-by-Packet
Generalized Processor Sharing (PGPS) mechanism combined with Leaky Bucket admission
control [1] with the objective of maximizing bandwidth available to the best-effort traffic
without adversely affecting the guarantee of the QoS traffic.
First, a multiplexing scheme, i.e, Two-Level Generalized Processor Sharing (2L-GPS), is
proposed. The scheme extends the Generalized Processor Sharing (GPS) multiplexing scheme
[1] from its original one-level multiplexing architecture to a two-level architecture.
Subsequently, we show that it is possible to compute performance guarantees for sources
constrained by leaky buckets in a 2L-GPS server when a certain condition is satisfied.
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In the last decade there has been a vast amount of work on providing service guarantees in
integrated service networks. The need to support a large variety of applications with diverse
quality of service (QOS) requirements such as voice, video-on-demand, etc., along with the
development of fiber-optics technologies, have fueled the need for a flow control scheme that
has the following three properties, i.e., efficiency, flexibility and analyzability [6]. In terms of
an efficient flow control, we give an example of a packet switched network. In a packet
switched network, a data session which typically has short bursts of high activity, followed by
lengthy inactive periods, can let other sessions utilize the bandwidth unused during its inactive
periods. By flexibility, we mean that the flow control scheme allows the network to treat users
differently, in accordance with their desired quality of service, without compromising the
fairness of the scheme, i.e., a few classes of users should not be able to degrade services to
other classes, to the extent that performance guarantees are violated. Lastly, the flow control
scheme needs to be analyzable to the extent that performance guarantees can be made in the
first place. In an environment where short-term demand for link usage frequently exceeds the
8
usable capacity, each of three properties of a flow control scheme above can apparently be in
conflict with the others. An approach to reconcile the conflict is proposed in [1] and its sequel
[2]. This approach employs PGPS (Packet-by-Packet Generalized Processor Sharing) in the
context of integrated service networks and combines this mechanism with Leaky Bucket
admission control in order to provide performance guarantees in a flexible environment.
An integrated service network should allow the provision of both best-effort and QoS
sessions. While not always in the forefront, as compared to the QoS traffic, the role of besteffort traffic is important in our conceptual framework for flow control. Another high-level
property which needs to be integrated in the flow control scheme is therefore the capability to
maximize the bandwidth available to best-effort traffic while satisfying the guarantees of the
QoS class. We thus devote this thesis to investigating the necessary refinements for the
seminal PGPS scheme combined with Leaky Bucket admission control in order to maximize
the bandwidth available to best-effort traffic without adversely affecting the guarantees of the
QoS class of traffic.
In this thesis we choose to focus on analytical rather than implementation oriented issues,
which does not mean that we do not consider the latter to be important. There is currently a
great pressure to choose appropriate packet schedulers for IP routers and ATM switches of
the future. We hope that this thesis, and the ideas that shape it, will be of some help to those
who have taken the exciting challenge of implementing these devices.
The remainder of this thesis can be outlined as follows. Chapter 2 extends the GPS
multiplexing scheme introduced in [1] from its original one-level multiplexing architecture to a
two-level architecture. The motivation, as will be apparent in Chapter 4, is to allow a greater
9
multiplexing flexibility so that a grouping policy can be incorporated on top of the
multiplexing framework. Zhang and Bennett [4] were the first to propose the Hierarchical
Generalized Processor Sharing (H-GPS) model to simultaneously support guaranteed realtime, rate-adaptive best-effort, and controlled link-sharing services. However, [4] does not
provide a thorough analysis in finding worst-case queueing delay and backlog for a leaky
bucket constrained session in a single H-GPS node. Following the definitions and properties
of the Two-Level GPS work discipline (2L-GPS), we therefore analyze a single 2L-GPS
server system in which the sessions are constrained by leaky buckets. The most important
result from our analysis is that it is possible to make worst-case queuing delay and backlog
guarantees for sources constrained by leaky buckets in a 2L-GPS environment, if a certain
condition is satisfied.
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necessary refinements for the seminal PGPS mechanism
combined with Leaky Bucket admission control [1] with the objective of maximizing
bandwidth available to the best-effort traffic without adversely affecting the guarantee of the
QoS traffic.
The contributions which follow from the investigation are as follow. We propose a
multiplexing scheme, i.e, 2L-GPS (Two-Level Generalized Processor Sharing), which extends
the GPS multiplexing scheme introduced in [1] from its original one-level multiplexing
architecture to a two-level architecture. Subsequently, we show that it is possible to compute
performance guarantees for sources constrained by leaky buckets in a 2L-GPS server, if the
weight assignment to each second-level session is such that φij ≥ ρij
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