Optimal Cell Loss Equalization for Video Multiplexers

Video traffic multiplexers in high speed ATM networks are prone to fairness problems with respect to the per-connection cell loss ratio experienced by multiplexed video sources. The problem is a result of the random, but fixed over time, relation of the frame transmission epochs that feed a multiplexer. This paper presents a solution to this fairness problem which is based on the enforcement of controlled per--connection delays. The amount of delay imposed on each source is calculated by an optimization process at connection admission and termination instants. Two different optimization objectives, one minimax and one minisum, are considered. Their performance and their relation to buffer space constraints is examined. The loss and delay performance of the scheme is also evaluated through simulations. In particular, very low per--connection delay variance is observed, indicating reduced jitter. Finally, two implementation alternatives of the scheme on an ATM network are presented: (a) as a protocol between multiplexer and sources and (b) as a non--work conserving service discipline for multiplexers. The engineering aspects and, in particular, the buffer demands of the two alternative implementations are discussed in detail

Impulsive Interference Avoidance in Dense Wireless Sensor Networks

ABSTRACT As with all wireless communication devices, wireless sensor networks (WSNs) are subject to interference from other users of the radio-frequency (RF) medium. Such interference is practically never random: originating in applications generally performing some practical and sensible activities, it naturally exhibits various regularities amounting to perceptible patterns, e.g., regularly-spaced short-duration impulses that correlate among multiple WSN nodes. If those nodes can recognize the interference pattern, they can benefit from steering their transmissions around it. This possibility has stirred some interest among researchers involved in cognitive radios, where special hardware has been postulated to circumvent non-random interference. Our goal is to explore ways of enhancing medium access control (MAC) schemes operating within the framework of traditional off-the-shelf RF modules applicable in low-cost WSN motes, such that they can detect interference patterns in the neighbourhood and creatively respond to them mitigating their negative impact on the packet reception rate. In this paper, we describe (a) a method for the post-deployment dynamic characterization of a channel aimed at identifying spiky interference patterns, (b) a way to incorporate interference models into an existing WSN emulator, and (c) the subsequent evaluation of a proof-of-concept MAC technique for circumventing the interference. We found that an interference-aware MAC can improve the packet delivery rates in these environments at the cost of increased latency. Notably, the latter is quite acceptable in the vast majority of WSN applications

Impulsive Interference Avoidance in Dense Wireless Sensor Networks

Abstract. Wireless sensor networks (WSNs) are subject to interference from other users of the radio-frequency (RF) medium. If the WSN nodes can recognize the interference pattern, they can benefit from steering their transmissions around it. This possibility has stirred some interest among researchers involved in cognitive radios, where special hardware has been postulated to circumvent non-random interference. Our goal is to explore ways of enhancing medium access control (MAC) schemes operating within the framework of traditional off-the-shelf RF modules applicable in low-cost WSN motes, such that they can detect interference patterns in the neighbourhood and creatively respond to them, mitigating their negative impact on the packet reception rate. In this paper, and based on previous work on the post-deployment characterization of a channel aimed at identifying "spiky" interference patterns, we describe (a) a way to incorporate interference models into an existing WSN emulator and (b) the subsequent evaluation of a proof-of-concept MAC technique for circumventing the interference. We found that an interference-aware MAC can improve the packet delivery rates in these environments at the cost of increased, but acceptable, latency

Cell loss equalization and time-parallel simulation for multimedia networks

Ph.D.Ian F. Akyildi

Optimal Cell Loss Equalization for Video Multiplexers

Video traffic multiplexers in high speed ATM networks are prone to fairness problems with respect to the per-connection cell loss ratio experienced by multiplexed video sources. The problem is a result of the random, but fixed over time, relation of the frame transmission epochs that feed a multiplexer. This paper presents a solution to this fairness problem which is based on the enforcement of controlled per--connection delays. The amount of delay imposed on each source is calculated by an optimization process at connection admission and termination instants. Two different optimization objectives, one minimax and one minisum, are considered. Their performance and their relation to buffer space constraints is examined. The loss and delay performance of the scheme is also evaluated through simulations. In particular, very low per--connection delay variance is observed, indicating reduced jitter. Finally, two implementation alternatives of the scheme on an ATM network are presented: (a) ..

Trace-Adaptive Fragmentation for Periodic Broadcast of VBR Video

Periodic broadcast schemes have been proposed as a scalable solution for the implementation of Video--on-- Demand (VoD) systems. Efficient periodic broadcast schemes fragment each video into a number of segments assuming that the videos are encoded using Constant Bit Rate (CBR) coders. We focus instead on the more efficient and commonplace class of Variable Bit Rate (VBR) encoded videos. The claim made in this paper is that the significant bit rate variability of VBR video requires a different fragmentation approach for the construction of periodic broadcast schedules. Rigid fragmentation techniques do not consider the particular video traces and may result in traffic which exceeds the available broadcast link capacity and can lead to increased data losses. Remarkably, all known periodic broadcast schemes use rigid fragmentation techniques. We introduce a new fragmentation scheme, Trace--Adaptive Fragmentation (TAF), which derives improved broadcast schedules for VBR video. Essentially..