SEMI-MARKOV APPROACH FOR DETERMINING THE RELIABILITY PARAMETERS OF COMPLEX SYSTEMS

In the reliability investigation of complex systems it sometimes becomes necessary to deal with distributions of a general type. That mainly occurs in the case of system repair works. This problem may be solved by modelling the system with a semi-Markov model. In this paper, we derive closed-form expressions for the determination of reliability parameters, like availability and mean sojourn times. These results are the generalization of those given in the literature for the Markov case. This fact is shown in the paper, as well

Dynamic Buffer Management for Multimedia QoS in Beyond 3G Wireless Networks

This paper investigates a dynamic buffer management scheme for QoS control of multimedia services in beyond 3G wireless systems. The scheme is studied in the context of the state-of-the-art 3.5G system i.e. the High Speed Downlink Packet Access (HSDPA) which enhances 3G UMTS to support high-speed packet switched services. Unlike earlier systems, UMTS-evolved systems from HSDPA and beyond incorporate mechanisms such as packet scheduling and HARQ in the base station necessitating data buffering at the air interface. This introduces a potential bottleneck to end-to-end communication. Hence, buffer management at the air interface is crucial for end-to-end QoS support of multimedia services with multiplexed parallel diverse flows such as video and data in the same end-user session. The dynamic buffer management scheme for HSDPA multimedia sessions with aggregated real-time and non real-time flows is investigated via extensive HSDPA simulations. The impact of the scheme on end-to-end traffic performance is evaluated with an example multimedia session comprising a real-time streaming flow concurrent with TCP-based non real-time flow. Results demonstrate that the scheme can guarantee the end-to-end QoS of the real-time streaming flow, whilst simultaneously protecting the non real-time flow from starvation resulting in improved end-to-end throughput performance

Performance modelling of a queue management scheme with rate control for HSDPA

High Speed Downlink Packet Access (HSDPA) is being increasingly deployed to enhance UMTS Radio Access Networks. Scheduling of Node B (base station) buffered user data for transmission over a shared radio channel is a key HSDPA functionality which enables queue management techniques to be utilized to improve QoS provisioning for mixed ‘multimedia’services. Thus, we have previously proposed and studied a Time-Space Priority (TSP) buffer management scheme for ‘multimedia’QoS control in HSDPA Node B. In this paper the scheme is extended to incorporate a threshold-based rate control mechanism which provides flow control between the RNC and Node B entities over the Iub interface to improve the QoS performance of non-real-time (NRT) streams in the multimedia flow. Mathematical and simulation models are developed for comparative analysis with the previously studied TSP scheme lacking rate control. The results demonstrate the performance improvement achievable with the joint implementation of TSP queue management scheme and Iub flow control mechanism(s)

Performance analysis of priority queueing systems in discrete time

The integration of different types of traffic in packet-based networks spawns the need for traffic differentiation. In this tutorial paper, we present some analytical techniques to tackle discrete-time queueing systems with priority scheduling. We investigate both preemptive (resume and repeat) and non-preemptive priority scheduling disciplines. Two classes of traffic are considered, high-priority and low-priority traffic, which both generate variable-length packets. A probability generating functions approach leads to performance measures such as moments of system contents and packet delays of both classes

High-Speed microphotonic optical header recognition

In this paper, we propose and demonstrate a new MicroPhotonic structure for optical packet header recognition based on the integration of an optical cavity, optical components and a photoreceiver array. The structure is inherently immune to optical interference thereby routing an optical header within optical cavities to different photoreceiver elements to generate the autocorrelation function, and hence the recognition, of the header using simple microelectronic circuits. The proof-of-concept is simulated and experimentally demonstrated

Distributed wireless optical communications for humanitarian assistance in disasters

We propose an optical wireless communication network architecture employing an all-optical central communication unit and optical transceiver units. The network can easily be installed when communication network facilities are partially damaged by a disaster. The network performance is simulated at 1Gbit/s, over 1km under different weather conditions

Throughput and delay optimization in WDM FDDI optical networks

The rapidly growing Internet traffic are driving the demands for higher transmission capacity and higher processing speed, especially for the backbone networks. To support such bandwidth usage an optical Fiber Distributed Data Interface Wavelengtg Division Multiplexed (FDDI/WDM) network is proposed, wherein the wavelength channels are amplified using Erbium-Doped Fiber Amplifiers (EDFA\u27s) to compensate for the losses over the optical fiber span. In this paper we investigate the network performance for both asynchronous and synchronous transmissions by measuring the amplified spontaneous emission (ASE) along the ring, the optical signal to noise ratio (OSNR) and the electrical SNR at different destinations. The effects of various network parameters such as synchronous bandwidth allocation and Target Token Ration Time (TTRT) on the network perfomrance are also presented. Results show that when FDDI is used in conjunction with WDM higher throughut and less delay are simutaneously achieved in comparison with FDDI standard networks