7 research outputs found
A first passage time problem for spectrally positive Lévy processes and its application to a dynamic priority queue
We study a first passage time problem for a class of spectrally positive Lévy processes. By considering the special case where the Lévy process is a compound Poisson process with negative drift, we obtain the Laplace–Stieltjes transform of the steady-state waiting time distribution of low-priority customers in a two-class M/GI/1 queue operating under a dynamic non-preemptive priority discipline. This allows us to observe how the waiting time of customers is affected as the policy parameter varies
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Performance analysis of error recovery and congestion control in high-speed networks
In the past few years, Broadband Integrated Services Digital Network (B-ISDN) has received increasing attention as a communication architecture capable of supporting multimedia applications. Among the techniques proposed to implement B-ISDN, Asynchronous Transfer Mode (ATM) is considered to be the most promising transfer technique because of its efficiency and flexibility.In ATM networks, the performance bottleneck of the network, which was once the channel transmission speed, is shifted to the processing speed at the network switching nodes and the propagation delay of the channel. This shift is because the high-speed channel increases the ratio of processing time to packet transmission time and also the ratio of propagation delay to packet transmission time. The increased processing overhead makes it difficult to implement hop-by-hop schemes, which may impose prohibitably high processing at each switching node. The increased propagation delay overhead makes traffic control in ATM a challenge since a large number of packets can be in transit between two ATM switching nodes. Because of these fundamental changes, control schemes developed for traditional networks may not perform efficiently, and thus, new network architectures (congestion control schemes, error control schemes, etc.) are required in ATM networks.In this dissertation, we first present an extensive survey of various traffic control schemes and network protocols for ATM networks. In this survey, possible traffic control schemes are examined, and problems of those schemes and their possible solutions are presented. Next, we investigate two key research issues in ATM networks (and other types of high-speed networks): the effects of protocol-processing overhead and the efficiency of traffic control schemes.We first investigate the effects of protocol-processing overhead on the performance of error recovery schemes. Specifically, we investigate the performance trade-offs between link-by-link and edge-to-edge error recovery schemes. Our results show that for a network with high-speed/low-error-rate channels, an edge-to-edge scheme gives a smaller delay than a link-by-link scheme. We then investigate the effectiveness of a priority packet discarding scheme, a congestion control mechanism suitable for high-speed networks. We derive loss probabilities for each stream and investigate the impact of burstiness of traffic streams on the performance of individual streams
Ku-band signal design study
Analytical tools, methods and techniques for assessing the design and performance of the space shuttle orbiter data processing system (DPS) are provided. The computer data processing network is evaluated in the key areas of queueing behavior synchronization and network reliability. The structure of the data processing network is described as well as the system operation principles and the network configuration. The characteristics of the computer systems are indicated. System reliability measures are defined and studied. System and network invulnerability measures are computed. Communication path and network failure analysis techniques are included
From burstiness characterisation to traffic control strategy : a unified approach to integrated broadbank networks
The major challenge in the design of an integrated network is the integration and
support of a wide variety of applications. To provide the requested performance
guarantees, a traffic control strategy has to allocate network resources according
to the characteristics of input traffic. Specifically, the definition of traffic characterisation
is significant in network conception. In this thesis, a traffic stream
is characterised based on a virtual queue principle. This approach provides the
necessary link between network resources allocation and traffic control.
It is difficult to guarantee performance without prior knowledge of the worst
behaviour in statistical multiplexing. Accordingly, we investigate the worst case
scenarios in a statistical multiplexer. We evaluate the upper bounds on the probabilities
of buffer overflow in a multiplexer, and data loss of an input stream. It is
found that in networks without traffic control, simply controlling the utilisation of
a multiplexer does not improve the ability to guarantee performance. Instead, the
availability of buffer capacity and the degree of correlation among the input traffic
dominate the effect on the performance of loss.
The leaky bucket mechanism has been proposed to prevent ATM networks from
performance degradation due to congestion. We study the leaky bucket mechanism
as a regulation element that protects an input stream. We evaluate the optimal
parameter settings and analyse the worst case performance. To investigate its effectiveness,
we analyse the delay performance of a leaky bucket regulated multiplexer.
Numerical results show that the leaky bucket mechanism can provide well-behaved
traffic with guaranteed delay bound in the presence of misbehaving traffic.
Using the leaky bucket mechanism, a general strategy based on burstiness characterisation,
called the LB-Dynamic policy, is developed for packet scheduling.
This traffic control strategy is closely related to the allocation of both bandwidth
and buffer in each switching node. In addition, the LB-Dynamic policy monitors
the allocated network resources and guarantees the network performance of each
established connection, irrespective of the traffic intensity and arrival patterns of
incoming packets. Simulation studies demonstrate that the LB-Dynamic policy is
able to provide the requested service quality for heterogeneous traffic in integrated
broadband networks