Lek Heng Ngoh

HDA: A hierarchical data aggregation scheme for sensor networks

Sensor networks are wireless networks that can obtain and process physical world information from scattered sensor devices. Due to the limited power, slow processor, and less memory in each device, routing protocols of sensor networks must be designed carefully. Recently, a data-centric scheme called directed diffusion has been proposed to provide efficient data transmission over sensor networks. In this paper, we enhance this scheme by a hierarchical data aggregation technique (HDA). Experiments demonstrate that our enhanced scheme can save transmission energy up to 50% over directed diffusion, without any reliability or delivery efficiency being compromised. At the same time, our scheme can facilitate greater data-level aggregation in data-centric routing.

A buffer-inventory-based dynamic scheduling algorithm for multimedia-on-demand servers

Abstract. We present a producer-consumer model of multimedia-on-demand (MOD) servers. The producer retrieves media data from a disk and places it into a set of buffers, while the consumer sends out the data in the buffers to the users. We develop for the producer a buffer-inventory-based dynamic scheduling (BIDS) algorithm that guarantees non-zero inventory and non-overflow of data in the buffers to meet the continuity requirement and no-loss of data for each media stream. The algorithm can deal with heterogeneous me dia streams as well as the transient circumstances upon service completions and arrivals of new requests. To smooth out the impact of bursty data of variable-bit-rate media streams and therefore increase the maximum admissible load of requests, we also introduce into the scheduling scheme a time-scale-dependent peak consumption rate and a virtual cycle time. Based on BIDS, an effective admission control mechanism can be easily established by checking two simple conditions respectively on the overall system load and buffer size. Our algorithm is very easy to implement. Experiments carried out with an actual disk system and real video stream data verify that it is more robust compared to static scheduling algorithms previously proposed in the literature, especially when handling variable-bit-rate media streams.n

Multimedia Networking Abstractions with Quality of Service Guarantees

The concept of schedulable region previously introduced to broadband networks with quality of service guarantees is extended to multimedia devices such as audio/video processing and disk storage units. The resulting multimedia capacity region characterized the amount of resources a physical device is able to provide under quality of service constraints. The modeling methodology supports a straightforward association of resources with logical objects and, thereby, the mapping of logical objects onto physical objects with quality of service guarantees. Examples showing the size and shape of the multimedia capacity region of various physical devices are given.

Identifying QoS violations through statistical end-to-end analysis

Multimedia transmission over the network is susceptible to various runtime impairments such as process failure, network congestion or link error. Existing work usually determines such quality of service (QoS) violations through condition–action rules, which trigger corresponding actions once pre-described conditions are satisfied. However, the results of such rigid rules are often not satisfactory in practice in that there has been little serious study with respect to the relationship between the root cause of a QoS violation and the observed violation phenomenon. n nIn this paper, we introduce a statistical approach to the analysis of QoS violations. We propose and validate through experiments that: (1) a type of QoS violation will present consistent symptoms in terms of the observed application performance and end-to-end traffic pattern. Such a violation can be recognized once the similar symptoms repeat during a QoS session. (2) QoS violations of different nature (e.g. caused by shortage of different resources) will present diverse symptoms. Using a set of end-to-end statistics, we are able to describe and differentiate between QoS violations. We propose a fast orthonormal algorithm for real-time training/classification of QoS violations and prove that this algorithm is universal approximation. We also extend the scope of hidden neurons from kernel functions to additive functions for higher classification accuracy. Our experiments validate our ideas and show the effectiveness of our approach in terms of training overhead and classification accuracy. Copyright

A time-scale dependent disk scheduling scheme for multimedia-on-demand servers

We present a producer-consumer model of multimedia-on-demand servers. The producer retrieves media data from a disk and places it into a set of buffers while the consumer sends out the data in the buffers to the users. We develop for the producer a time-scale dependent buffer-inventory-based dynamic scheduling scheme named /spl sigma/-BIDS which guarantees to meet the continuity requirement and no-loss of data for each media stream. The scheme introduces a time-scale dependent peak consumption rate and a virtual cycle time to smooth out the impact of bursty data of variable-bit-rate streams, thus improving the maximum admissible load of requests. A straightforward admission control mechanism with quality-of-service guarantees is then established based on two simple conditions respectively on load and buffer size. Our scheduling scheme is very easy to implement, and experiments carried out with an actual disk system and real video stream data verify the effectiveness of the scheme.

A CORBA-based real-time stream service for ATM networks

Off-the-shelf CORBA implementations are not suitable for real-time applications due to their high processing overheads. A CORBA-based real time stream service (RTSS) is proposed to augment the multimedia handling capability of current CORBA implementations. RTSS provides object-oriented application programming interfaces (APIs) for the rapid development of applications involving exchanges of time-constraint continuous media data. These APIs allow applications to specify their network and host QoS requirements and honor them if they are admissible. RTSS operates directly over ATM adaptation layers but also supports legacy UDP and TCP for interoperability with existing TCP/IP applications. A high-level design overview is given.

End-to-end diagnosis of QoS violations with neural network

In this paper, we introduce a novel end-to-end approach to QoS management with respect to the diagnosis of QoS violations. We first use a set of end-to-end flow traffic statistics to describe a QoS violation. Subsequently, neural network techniques are engaged to identify and differentiate QoS violations through classification of the collected statistics. Through experiments, we find that our scheme outperforms traditional rule-based methods which require clear margins of QoS parameters in asserting a QoS violation.

Active multicast service architecture for user-customized multimedia data transmission over ATM networks

This paper proposes a new ATM multicast scheme within the framework of an Active Multicast Service Architecture (AMSA) that supports user customization of multicast service. The customization is achieved by injecting and invoking user specific programs to shared network resources such as routers and switches. The multicast scheme also allows dynamic joining and/or leaving of members of different capabilities and quality of service requirements. A prototype of the multicast scheme was developed to verify the major functions of the AMSA and to demonstrate the feasibility of customizing network services within the active service architectural framework. The prototype supports QOS negotiation, non-uniform links QOS, resource reservation and filter program injection. The development platform sued consists of virtual ATM switches inter- connected via a real FORE ATM switch. The data links between these virtual switches are AAL-5 virtual circuits that enable actual QOS reservation. The signaling of the virtual switches is implemented via CORBA links connecting the CORBA daemons residing in the virtual switches. Experimental results show that the prototype of ATM multicast scheme is efficient and flexible in satisfying the requirements of heterogeneous users.

Design and implementation of a manageable B-ISDN host interface

This paper presents a solution to provide connectivity between a general-purpose workstation and a public broadband-ISDN trial system. The solution involves the creation of a low-level network layer software which is transparent to the existing TCP/IP protocol stack supported by the workstation operating system. This solution allows existing applications to communicate over the B-ISDN without modification, and future applications to be developed efficiently. Network management capability is also provided at the interface software to enable future research on terminal-end B-ISDN management using a standard network management framework.