Search

Fiber-Wireless (FiWi) networks typically combine an optical access network with a wireless access network so as to build on the respective strengths of the optical and wireless network technologies. Prior analytical throughput-delay studies of FiWi networks have typically considered heavy-loaded traffic models, i.e., constantly backlogged source nodes. In contrast, in this paper we present a more general comprehensive FiWi network throughput-delay analysis that encompasses Poisson (non-heavy) as well as heavy-loaded input traffic models. In addition, our analysis covers bandwidth assignments of wireless channels both at the hop distance level and at the node level, as well as a queuing model of dynamic bandwidth allocation in the optical access network. Our analysis provides insightful guidelines for setting the channel access probabilities for source traffic and relay traffic in FiWi networks. Our numerical evaluations demonstrate that prior studies which considered only heavy traffic loads gave misleading results for the delay performance of well-known access probability assignments. We correct and clarify these misleading results with our more general analysis for non-heavy traffic. [ABSTRACT FROM AUTHOR]

In a hybrid PON/xDSL access network, multiple customer premise equipment (CPE) nodes connect over individual digital subscriber lines (DSLs) to a drop-point device. The drop-point device, which is typically reverse powered from the customer, is co-located with an optical network unit (ONU) of the passive optical network (PON). We demonstrate that the drop-point experiences very high buffer occupancies when no flow control or standard Ethernet PAUSE frame flow control is employed. In order to reduce the buffer occupancies in the drop-point, we introduce two gated flow control protocols that extend the polling-based PON medium access control to the DSL segments between the CPEs and the ONUs. We analyze the timing of the gated flow control mechanisms to specify the latest possible time instant when CPEs can start the DSL upstream transmissions so that the ONU can forward the upstream transmissions at the full PON upstream transmission bit rate. Through extensive simulations for a wide range of bursty traffic models, we find that the gated flow control mechanisms, specifically, the ONU and CPE grant sizing policies, enable effective control of the maximum drop-point buffer occupancies. [ABSTRACT FROM AUTHOR]

Abstract: A wide array of dynamic bandwidth allocation (DBA) mechanisms have recently been proposed for improving bandwidth utilization and reducing idle times and packet delays in passive optical networks (PONs). The DBA evaluation studies commonly assumed that the report message for communicating the bandwidth demands of the distributed optical network units (ONUs) to the central optical line terminal (OLT) is scheduled for the end of an ONU's upstream transmission, after the ONU's payload data transmissions. In this paper, we conduct a detailed investigation of the impact of the report message scheduling (RMS), either at the beginning (i.e., before the pay load data) or the end of an ONU upstream transmission on PON performance. We analytically characterize the reduction in channel idle time with reporting at the beginning of an upstream transmission compared to reporting at the end. Our extensive simulation experiments consider both the Ethernet Passive Optical Networking (EPON) standard and the Gigabit PON (GPON) standard. We find that for DBAs with offline sizing and scheduling of ONU upstream transmission grants at the end of a polling cycle, which processes requests from all ONUs, reporting at the beginning gives substantial reductions of mean packet delay at high loads. For high-performing DBAs with online grant sizing and scheduling, which immediately processes individual ONU requests, or interleaving of ONUs groups, both reporting at the beginning or end give essentially the same average packet delays. [Copyright &y& Elsevier]

H.264/Advanced Video Coding (AVC) employs classical bi-directional encoded (B) frames that depend only on intra-coded (I) and predictive encoded (P) frames. In contrast, H.264 Scalable Video Coding (SVC) employs hierarchical B frames that depend on other B frames. A fundamental question is how many priority levels single-layer H.264 video encodings require when the encoded frames are statistically multiplexed in transport networks. We conduct extensive simulation experiments with a modular statistical multiplexing structure to uncover the impact of priority levels for a wide range of multiplexing policies. For the bufferless statistical multiplexing of both H.264/AVC and SVC we find that prioritizing the frames according to the number of dependent frames can increase the number of supported streams up to approximately 8%. In contrast, for buffered statistical multiplexing with a relatively small buffer size, frame prioritization does generally not increase the number of supported streams. [ABSTRACT FROM PUBLISHER]

While the hierarchical B frames based Scalable Video Coding (SVC) extension of the H.264/AVC standard achieves significantly improved compression over the initial H.264/AVC codec, the SVC video traffic is significantly more variable than H.264/AVC traffic. The higher traffic variability of the SVC encoder can lead to smaller numbers of streams supported with bufferless statistical multiplexing than with the H.264/AVC encoder (and even less streams than with the MPEG-4 Part 2 encoder) for prescribed link capacities and loss constraints. In this paper we examine the implications of video traffic smoothing on the numbers of statistically multiplexed H.264 SVC, H.264/AVC, and MPEG-4 Part 2 streams, the bandwidth requirements for streaming, and the introduced delay. We identify the levels of smoothing that ensure that more H.264 SVC streams than H.264/AVC streams can be supported. For a basic low-complexity smoothing technique that is readily applicable to both live and prerecorded streams, we identify the levels of smoothing that give (bufferless) statistical multiplexing performance close to an optimal off-line smoothing technique. We thus characterize the trade-offs between increased smoothing delay and increased statistical multiplexing performance for both H.264/AVC, which employs classical B frames, and H.264 SVC, which employs hierarchical B frames. We similarly identify the buffer sizes for the buffered multiplexing of unsmoothed H.264 SVC, H.264/AVC, and MPEG-4 Part 2 streams that give close to optimal performance. [ABSTRACT FROM AUTHOR]

Packet-switched unidirectional and bidirectional ring wavelength division multiplexing (WDM) networks with destination stripping provide an increased capacity due to spatial wavelength reuse. Besides unicast traffic, future destination stripping ring WDM networks also need to support multicast traffic efficiently. This article examines the largest achievable transmitter throughput, receiver throughput, and multicast throughput of both unidirectional and bidirectional ring WDM networks with destination stripping. A probabilistic analysis evaluates both the nominal capacity, which is based on the mean hop distances traveled by the multicast packet copies, and the effective capacity, which is based on the ring segment with the highest utilization probability, for each of the three throughput metrics. The developed analytical methodology accommodates not only multicast traffic with arbitrary multicast fanout but also unicast and broadcast traffic. Numerical investigations compare the nominal transmission, receiver, and multicast capacities with the effective transmission, receiver, and multicast capacities and examine the impact of number of ring nodes and multicast fanout on the effective transmission, reception, and multicast capacity of both types of ring networks for different unicast, multicast, and broadcast traffic scenarios and different mixes of unicast and multicast traffic. The presented analytical methodology enables the evaluation and comparison of future multicast-capable medium access control (MAC) protocols for unidirectional and bidirectional ring WDM networks in terms of transmitter, receiver, and multicast throughput efficiency. [ABSTRACT FROM AUTHOR]

We examine and model the bit rate variability-distortion (VD) curve of -4 Part 2 variable bit rate (VBR) video encodings. The VD curve has important applications for evaluating the statistical multiplexing of streaming video. We show that the concave VD curve shape at high compression ratios, or equivalently large quantization scales, is influenced by both the texture and the motion information. Based on this insight, we first develop a general VD curve model by analytically expressing the VD curve in terms of elementary statistics (mean, variance, covariance) of the numbers of motion and texture coding bits. In a second step we develop and validate linear and quadratic models for the elementary texture and motion bit statistics, whereby the model parameters are obtained from only two sample encodings. The texture and motion bit models are then employed in our general VD curve model. This work extends our previous work on piecewise models of the VD curve. The texture and motion based VD model obtained from two sample encodings has comparable accuracy to a piece- wise model based on three sample encodings. In addition, the texture and motion based VD model provides fundamental insights into how texture and motion affect traffic variability. [ABSTRACT FROM AUTHOR]

WDM EPONs are rapidly becoming mature. In this article we briefly review the state of the art of cost reduction, colorless ONUs, and WDM PONs. We then lift the veil of future WDM EPONs, and elaborate on evolutionary cost-effective upgrades of WDM EPONs and their all-optical WDM integration with Ethernet-based metropolitan area networks to provide transparent connections at the wavelength and sub-wavelength granularity on demand between ONUs residing in different WDM EPONs. [ABSTRACT FROM AUTHOR]

Routing algorithms with time and message complexities that are provably low and independent of the total number of nodes in the network are essential for the design and operation of very large scale wireless mobile ad hoc networks (MANET5). In this paper, we develop and analyze Cluster Overlay Broadcast (COB), a low-complexity routing algorithm for MANETs. COB runs on top of a one-hop cluster cover of the network, which can be created and maintained using, for instance, the Least Cluster Change (LCC) algorithm. We formally prove that the LCC algorithm maintains a cluster cover with a constant density of cluster leaders with minimal update cost. COB discovers routes by flooding (broadcasting) route requests through the network of cluster leaders with a doubling radius technique. Building on the constant density property of the network of cluster leaders, we formally prove that, if there exists a route from a source to a destination node with a minimum hop count of Δ, then COB discovers a route with at most O(Δ) hops from the source to the destination node in at most O(Δ) time and by sending at most Q(Δ²) messages. We prove this result for arbitrary node distributions and mobility patterns and also show that COB adapts asymptotically optimally to the mobility of the nodes. In our simulation experiments, we examine the network layer performance of COB, compare it with Dynamic Source Routing, and investigate the impact of the MAC layer on COB routing. [ABSTRACT FROM AUTHOR]

WDM EPONs not only allow for cautious pay-as-you- grow upgrades of single-channel TDM EPONs but also avoid linearly increasing polling cycle times for an increasing number of ONUs. In this article, we first provide a comprehensive overview of the state-of-the-art of TDM EPONs and recently reported dynamic bandwidth allocation algorithms, including decentralized scheduling schemes. After reviewing previous work on WDM EPONs, we address the requirements of WDM upgraded EPONs and make recommendations on an evolutionary WDM upgrade at the architecture, protocol, and dynamic bandwidth allocation algorithm levels, taking backward compatibility with MPCP and future-proofness against arbitrary WDM ONU structures into account. We describe and compare online and offline scheduling paradigms for WDM EPONs. Our simulation results indicate that online scheduling can achieve lower delays, especially at high loads. We outline areas of future research on WDM EPONs. [ABSTRACT FROM AUTHOR]

Fiber to the home in the U.S. market has not been deployed as rapidly as many had hoped or predicted. We examine some of the historical, competitive, and economic reasons for this. We argue that, from a competitive service perspective, it may be difficult to construct compelling business cases for large-scale deployment without either a technical need for fiber, or significant changes in either public policy or industrial organization. [ABSTRACT FROM AUTHOR]

Video streaming is expected to account for a large portion of the traffic in future networks, including wireless networks. It is widely accepted that the user datagram protocol (UDP) is the preferred transport protocol for video streaming and that the transmission control protocol (TCP) is unsuitable for streaming. The widespread use of UDP, however, has a number of drawbacks, such as unfairness and possible congestion collapse, which are avoided by TCP. In this paper we investigate the use of TCP as the transport layer protocol for streaming video in a multi-code CDMA cellular wireless system. Our approach is to stabilize the TCP throughput over the wireless links by employing a recently developed simultaneous MAC packet transmission (SMPT) approach at the link layer. We study the capacity, i.e. the number of customers per cell, and the quality of service for streaming video in the uplink direction. Our extensive simulations indicate that streaming over TCP in conjunction with SMPT gives good performance for video encoded in a closed loop, i.e. with rate control. We have also found that TCP is unsuitable (even in conjunction with SMPT) for streaming the more variable open-loop encoded video. Copyright © 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Investigates the delivery of layered encoded video through caches. Development of a model of layered video streaming with proxy; Examination of optical caching strategies; Numerical results.

Abstract: The use of video in distance education courses has a long tradition, with many colleges and universities having been delivering distance education courses with video since the 80''s using the Instructional Television Fixed Service (ITFS) and cable television. With the emergence of the Internet and the increased access bandwidths from private homes to the Internet, the delivery of distance education video via web-streaming has become more widespread and appears poised to replace the delivery of distance education video through ITFS/cable TV. At this juncture in the history of distance education video delivery it is important to take the student attitudes toward these different forms of educational video delivery into consideration. This naturalistic evaluation study examined and compared the attitudes of a total of close to 360 students who had taken distance education classes with video, whereby approximately 180 of the students had participated in classes with ITFS/cable TV video delivery and approximately 180 students had taken classes with web-streaming video delivery. The overall student satisfaction was found to be approximately the same with either form of distance education video delivery. However, there were statistically significant differences in the student attitudes towards specific aspects of the distance education video, such as perceived video quality, technical problems, and preferences for control over the instructional flow. [Copyright &y& Elsevier]