Cormac J. Sreenan

Resource management system for a broadband multipoint bridge

The use of a bridge (also known as a multipoint central unit) to enable multipoint communications over point to point narrowband-ISDN connections is well established. We deal with multipoint bridging for a broadband network environment. We explain the benefits of employing a bridge in that context and highlight the new design problems and challenges. Of particular importance is the need for a bridge resource management system which can be used in conjunction with end to end contracts for quality of service. We describe a model for managing bridge resources based on the estimated requirements of audio and video processing functions. Aspects of the initial system design are presented.

Delay reduction techniques for playout buffering

Receiver synchronization of continuous media streams is required to deal with delay differences and variations resulting from delivery over packet networks such as the Internet. This function is commonly provided using per-stream playout buffers which introduce additional delay in order to produce a playout schedule which meets the synchronization requirements. Packets which arrive after their scheduled playout time are considered late and are discarded. In this paper, we present the Concord algorithm, which provides a delay-sensitive solution for playout buffering. It records historical information and uses it to make short-term predictions about network delay with the aim of not reacting too quickly to short-lived delay variations. This allows an application-controlled tradeoff of packet lateness against buffering delay, suitable for applications which demand low delay but can tolerate or conceal a small amount of late packets. We present a selection of results from an extensive evaluation of Concord using Internet traffic traces. We explore the use of aging techniques to improve the effectiveness of the historical information and hence, the delay predictions. The results show that Concord can produce significant reductions in buffering delay and delay variations at the expense of packet lateness values of less than 1%.

A Network Based Replay Portal

A network based video replay service utilizing broadband technologies on the internet. A replacement for current analog or digital TV offerings that offer the same quality and user experience. The capacity used by current offerings (e.g. on a cable access network) will be freed up for use by the new service. The current schedule based broadcast paradigm users are accustomed to is emulated while at the same time offering on-demand viewing based on personal preference or subscription profile. This hybrid offering can lead to bandwidth savings in the access network with interaction of this service with other services on a common packet based infrastructure.

mmdump: a tool for monitoring internet multimedia traffic

Internet multimedia traffic is increasing as applications like streaming media and packet telephony grow in popularity. It is important to monitor the volume and characteristics of this traffic, particularly because its behavior in the face of network congestion differs from that of the currently dominant TCP traffic. To monitor traffic on a high-speed link for extended periods, it is not practical to blindly capture all packets that traverse the link. We present mmdump, a tool that parses messages from RTSP, H.323 and similar multimedia session control protocols to set up and tear down packet filters as needed to gather traces of multimedia sessions. Unlike tcpdump, dynamic packet filters are necessary because these protocols dynamically negotiate TCP and UDP port numbers to carry the media content. Our tool captures only packets of interest for optional storage and further analysis, thus greatly reducing resource requirements. This paper presents the design and implementation of mmdump and demonstrates its utility in monitoring live RTSP and H.323 traffic on a commercial IP network. The preliminary results obtained from these measurements are presented.

A context aware wireless body area network (BAN)

In monitoring a patients real-time vital signs through Body Area Networks (BAN), rich data sources are communicated to medical practitioners. The benefit of BANs may be negated if medical practitioners are overloaded with streams of BAN data. It is essential that data is delivered in a timely context aware manner. In this paper a BAN designed for falls assessment among elder patients (65+ years) is presented, with an emphasis on the communication scheme chosen. The FrameComm MAC protocol described in this paper employs three data management techniques, 1) message priority, 2) opportunistic aggregation and 3) an adaptive duty cycle, all of which are designed to ensure that patient vital signs (i.e. data packets) are delivered under a variety of network loads. The protocol is evaluated using a small laboratory network, initially configured to communicate Beat-to-Beat (continuous blood pressure) readings when a patient goes from a sitting to a standing position and then with added ECG (ElectroCardioGram) readings.

Car-Park Management using Wireless Sensor Networks

A complete wireless sensor network solution for carpark management is presented in this paper. The system architecture and design are first detailed, followed by a description of the current working implementation, which is based on our DSYS25z sensing nodes. Results of a series of real experimental tests regarding connectivity, sensing and network performance are then discussed. The analysis of link characteristics in the car-park scenario shows unexpected reliability patterns which have a strong influence on MAC and routing protocol design. Two unexpected link reliability patterns are identified and documented. First, the presence of the objects (cars) being sensed can cause significant interference and degradation in communication performance. Second, link quality has a high temporal correlation but a low spatial correlation. From these observations we conclude that a) the construction and maintenance of a fixed topology is not useful and b) spatial rather than temporal message replicates can improve transport reliability

An adaptive predictor for media playout buffering

Receiver playout buffers are required to smooth network delay variations for multimedia streams. Playout buffer algorithms such as those commonly used in the Internet, autoregressively measure the network delay and variation and adjust the buffer delay accordingly, to avoid packets arriving too late. In this work, we attempt to adjust the buffer delay based on a prediction of the network delay and a similar measure of variation. The philosophy here is that the use of an accurate prediction will adjust the buffer delay more effectively by tracking rapid fluctuations more accurately. Proper buffer delay can lead to either (or both) a lower total end-to-end delay for a fixed packet lateness percentage or fewer late packets for a fixed total end-to-end delay which are both important metrics for applications such as IP telephony. We present a playout algorithm based on a simple normalized least-mean-square (NLMS) adaptive predictor and demonstrate using Internet packet traces that it can yield reductions in average total end-to-end delays.

The development of a novel minaturized modular platform for wireless sensor networks

Wireless sensor networks are collections of autonomous devices with computational, sensing and wireless communication capabilities. Research in this area has been growing in the past few years given the wide range of applications that can benefit from such a technology. In this paper, the development of a highly modular and miniaturized wireless platform for sensor networks is described. The system incorporates a radio transceiver (in the 2.4 GHz ISM Band) with embedded protocol software to minimize power consumption and maximize data throughput. Additional input capability for sensor and actuator integration can be incorporated seamlessly due to the modular nature of the system. The total system is packaged in a modular 25 mm cubed form factor. A smaller, (10 mm cubed), prototype is currently under development. Ongoing development of highly miniaturized nodes is discussed.

A simple loss differentiation approach to layered multicast

Layered multicast is a promising technique for broadcasting adaptive-quality TV video to heterogeneous receivers. While several-layered multicast approaches have been proposed, prior work has identified several problems including significant and persistent instability in video quality, arbitrary unfairness with other sessions, low access link utilization due to conservative bandwidth allocation, and problems with receiver synchronization. In this paper we propose a new layered multicast scheme, where we exploit a simple, coarse-grained, two-tier loss differentiation architecture to achieve stable and fair bandwidth allocation for viewers. Despite the simplicity of our loss differentiation model, we show that it achieves most of the benefits of complex and costly priority dropping schemes. In addition, our protocol is receiver-driven and thus retains the incentives to limit bandwidth usage that are not present in existing priority dropping schemes.

/spl mu/-MAC: an energy-efficient medium access control for wireless sensor networks

For the long-term deployment of wireless sensor networks, energy efficient MAC protocols are necessary. The transceiver of a sensor node should only consume energy while actively taking part in communication. Energy consumption in idle mode should be avoided as much as possible. In this paper it is shown how application layer knowledge in the form of flow specifications can be used to improve the energy properties of a MAC protocol. A new protocol, named /spl mu/-MAC, is proposed and evaluated through simulations.