Media handling aspects of multimedia conferencing in broadband wireless ad hoc networks

The emergence of broadband wireless technologies has made broadband wireless ad hoc networks a reality. Broadband wireless ad hoc networks are infrastructure-less and can be used in a wide range of scenarios in private, public, commercial, and military settings. Multimedia conferencing is an important application area. Its two main components are signaling and media handling. This article focuses on the media handling aspects or multimedia conferencing in broadband wireless ad hoc networks, with a critical review of the state of the art and a proposed novel architecture. The main components of this architecture are a distributed mixing system and a self-organizing system. The distributed mixing system is a two-level structure. The first level is a full mesh network of active nodes that act as media mixers. The second level is made up of passive nodes that rely on the mixers in the first level. Each second-level node is connected to a first-level node. The self-organizing system is based on a resource efficient scheme that provides for the automatic allocation (or deallocation) of mixers when the network grows (or shrinks). Furthermore, it enables the automatic assignment of new nodes to mixers when they join the conference. We have built a proof-of-concept prototype of the architecture and have evaluated the self-organizing system through simulations. We have simulated conferences and observed how mixers are allocated and deallocated. The simulations show that our self-organizing system utilizes resources efficiently in most cases.     

A dynamic channel assignment scheme for clustered multihop cellular networks

Whereas cellular systems have traditionally adopted single‐hop transmissions between the mobile station (MS) and the base station (BS), researchers expect multihop transmission to be utilised in the future. Cellular systems present several challenges, such as channel assignment, which are exacerbated by multimedia service traffic and an increasing number of subscribers. Recently, a clustered multihop cellular network (cMCN) architecture that complements traditional cellular systems has been proposed and studied using fixed channel assignment (FCA). However, the performance of FCA is limited when the traffic pattern varies in a service area. This paper proposes the use of dedicated information ports (DIPs) as clusterheads in cMCN, followed by a multihop dynamic channel assignment (mDCA) scheme. The mDCA works by assigning channels based on information about interference in surrounding cells. Two different channel searching strategies are developed and evaluated. Through computer simulation, we show that the proposed mDCA is able to achieve a significantly improved capacity which is maintained when the number of system channels is increased. Finally, issues regarding the implementation of the mDCA and future work on this topic are discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

Multipoint multimedia conferencing

The development of multipoint multimedia services for conferencing is described. The use of integrated services digital network (ISDN) as part of the work carried out in the European collaborative projects Multipoint Interactive Audiovisual Communication (MIAC) and Multipoint Interactive Audiovisual System (MIAS) is emphasized. The history of multipoint teleconferencing, the different types of multipoint conferencing systems, and protocol requirements for multipoint multimedia conferencing systems are also discussed     

IP-networked multimedia conferencing

This article looks at video conferencing, specifically the VideoTalks system developed by AT&T Labs. This system was designed to alleviate some of the problems of both user experience and audiovisual signal quality. It allows talks and presentations generated in one auditorium or conference room to be received in other conference rooms, multicast to desktop computers, and received at home or on the road. VideoTalks is a prototypical system that can be retrofitted to provide for a variety of Internet services, such as remote learning, narrowcasting to niche audiences, video telephone, video conferencing, low cost video-on-demand, etc. An effort was also made to make the system function without a full-time operator     

A multimedia interactive conferencing application for personalworkstations

The multimedia interactive conferencing application (MICA), a personal-workstation application for multipoint visual teleconferencing, is described. MICA allows people at two or more locations to share visual material such as documents, photographs, and computer screens in a highly interactive way. It supports the distribution, storage, retrieval, and high-quality display of visuals, real-time interaction by pointing and annotation, and meeting services facilities. The context of multimedia teleconferencing and computer-supported cooperative work is established, relating earlier research to the design of MICA. The services MICA offers are outlined. The handling, compression, and display of multiple media, and the design of a suitable user interface for MICA are discussed     

Handover in multihop cellular networks [Accepted from Open Call]

This article introduces various handover scenarios in multihop cellular networks. In addition, this article presents handover schemes where relay stations are located either inside a cell or on the boundary between two adjacent cells and investigates the effects of the deployment position of relay stations to handover performance. The simulation results show that multihop cellular networks for both deployment scenarios can achieve 90 percent throughput increase over single-hop cellular networks. The results also show that the overall throughput of the multihop cellular networks with relay stations inside a cell is higher than for those with relay stations on the boundary between two adjacent cells, whereas the opposite is observed for the throughput of cell-boundary users. The intercell handover latency in multihop cellular networks is increased by 20 ~ 56 percent compared with that in singlehop cellular networks because of the increased number of handovers and signaling overhead. However, by deploying relay stations on the boundary between two adjacent cells, the service-interruption time caused by inter-cell handover is reduced by 80 percent compared with that of single-hop cellular networks.     

Analysis and modeling of upstream throughput in multihop packet CDMA cellular networks

We consider the problem of throughput modeling of wireless multihop packet CDMA networks with cellular overlay using simple forwarding strategies in the upstream. Considering the effect of shadowing and distance-dependent path loss, we approximate the probability density of interference at each base station (BS) and compare numerical and simulation results for different path-loss parameters. We derive the probability density of the received power at each BS due to transmission of one packet from a random node, as well as the probability distribution of the number of packets received at each node per time slot. Subsequently, we use the above results to approximate the probability density of the total received power at each BS based on calculations of moments. We observe that the probability density of intercell interference due to transmissions from terminals and routers may be approximated by normal and log-normal densities, respectively. We quantify the network performance based on throughput, total consumed power, and outage probability for different system parameters. For homogeneous link efficiencies, introducing routers into the network while reducing the transmission power increases the mean and variance of interference to the desired signal, hence higher outage probability. However, there are ample opportunities inherent to multihop structure, applicable to any of the physical, data link, and network layers, which help increase the overall achievable network throughput.     

Admission-control policies for multihop wireless networks

In this paper, we investigate the admission-control problem for voice traffic in fixed-route circuit-switched wireless networks. We consider coordinate-convex admission-control policies and a blocked-calls-cleared mode of operation, in conjunction with the usual assumptions on the voice process statistics. These conditions result in a product-form stationary distribution for the voice state of the system, which facilitates the evaluation of network performance. However, to determine the optimal policy a large state space must be searched. We develop a recursive procedure to accelerate the evaluation of a large number of different admission-control policies, and a descent-search method to reduce significantly the number of policies that must be evaluated in searching for the optimal one. The numerical examples we present indicate that reduced blocking probability (or increased throughput) can be obtained by administering active admission control. The degree of improvement is highest in moderately overloaded traffic conditions, but it is typically small in low-capacity networks (at all loads). However, in applications where the performance measure associates different revenues or costs with the various call types, considerable improvement can be obtained when admission control is used.     

An enhanced handoff control scheme for multimedia traffic in cellular networks

This letter presents an enhanced handoff control scheme allowing dynamic bandwidth sharing between different types of traffic for improving bandwidth utilization in multimedia mobile cellular networks. Performance results for the proposed scheme are obtained analytically and by simulation. The results demonstrate superior efficiency achieved by the proposed scheme.     

Managing data in distributed multimedia conferencing applications

Managing packets in a distributed multimedia environment involves coordinating and synchronizing multiple data streams. The Ensembles Coordination Program provides the required coordination, reduces delay using path selection and message rebroadcasting, and allows the end application to manage the synchronization within the streams     

An integrated adaptive bandwidth-management framework for QoS-sensitive multimedia cellular networks

Bandwidth is an extremely valuable and scarce resource in a wireless network. Therefore, efficient bandwidth management is necessary in order to provide high-quality service to users in a multimedia wireless/mobile network. In this paper, we propose new online bandwidth-management algorithms for bandwidth reservation, call admission, bandwidth migration, and call-preemption strategies. These techniques are combined in an integrated framework that is able to balance the traffic load among cells accommodating heterogeneous multimedia services while ensuring efficient bandwidth utilization. In addition, our online framework to adaptively control bandwidth is a cell-oriented approach that has low complexity, which makes it practical for real cellular networks. Simulation results indicate the superior performance of our bandwidth-management framework to strike the appropriate performance balance between contradictory quality-of-service requirements.     

Scheduling algorithms for multihop radio networks

Algorithms for transmission scheduling in multihop broadcast radio networks are presented. Both link scheduling and broadcast scheduling are considered. In each instance, scheduling algorithms are given that improve upon existing algorithms both theoretically and experimentally. It is shown that tree networks can be scheduled optimally and that arbitrary networks can be scheduled so that the schedule is bounded by a length that is proportional to a function of the network thickness times the optimum. Previous algorithms could guarantee only that the schedules were bounded by a length no worse than the maximum node degree times optimum. Since the thickness is typically several orders of magnitude less than the maximum node degree, the algorithms presented represent a considerable theoretical improvement. Experimentally, a realistic model of a radio network is given and the performance of the new algorithms is studied. These results show that, for both types of scheduling, the new algorithms (experimentally) perform consistently better than earlier methods     

Coordination and control of multimedia conferencing

It is shown that multimedia, multipoint conferencing systems create important requirements for the networks they use to transmit information among conference participants. These requirements, which stem from the need for conferencing systems to emulate the richness of control present in face-to-face conversations, may extend from the user interface to the control and coordination of communication networks. The user interface of a conferencing system should present users with the means to control the conduct of meetings, as well as the exchange and presentation of multimedia information. The virtual meeting room metaphor of Rapport, which provides the foundation for this system's user interface, is described. The creation and communication of multimedia information, conferencing over multiple and integrated networks, and requirements for multiport communications are discussed     

Cooperative multihop broadcast for wireless networks

We address the minimum-energy broadcast problem under the assumption that nodes beyond the nominal range of a transmitter can collect the energy of unreliably received overheard signals. As a message is forwarded through the network, a node will have multiple opportunities to reliably receive the message by collecting energy during each retransmission. We refer to this cooperative strategy as accumulative broadcast. We seek to employ accumulative broadcast in a large scale loosely synchronized, low-power network. Therefore, we focus on distributed network layer approaches for accumulative broadcast in which loosely synchronized nodes use only local information. To further simplify the system architecture, we assume that nodes forward only reliably decoded messages. Under these assumptions, we formulate the minimum-energy accumulative broadcast problem. We present a solution employing two subproblems. First, we identify the ordering in which nodes should transmit. Second, we determine the optimum power levels for that ordering. While the second subproblem can be solved by means of linear programming, the ordering subproblem is found to be NP-complete. We devise a heuristic algorithm to find a good ordering. Simulation results show the performance of the algorithm to be close to optimum and a significant improvement over the well known BIP algorithm for constructing energy-efficient broadcast trees. We then formulate a distributed version of the accumulative broadcast algorithm that uses only local information at the nodes and has performance close to its centralized counterpart.     

基于SIP的多媒体会议分布式管理架构的设计

与会者及设备在地理上多处分布的大规模多媒体会议系统的一个重要设计思想就是要提高会议管理架构的可伸缩性.文章介绍了基于会话初始协议(SIP)的多媒体会议分布式管理架构的设计,并将策略管理技术引入到分布式管理架构中,从而为解决会议系统的缩放性、扩展性问题提供了一种新途径.     

基于JAIN SIP的多媒体会议系统中发言权控制

发言权控制(Floor Control)是多媒体会议中会议控制的一部分,用来协调参与者对底层共享资源的使用,它直接关系到会议的服务质量.文章利用会话初始协议(SIP)的可扩展性,在SUN公司为实现SIP应用而提供的一套Java接口(JAIN SIP)架构下设计并实现了SIP多媒体会议系统的发言权控制系统,该系统具有控制方式多样化,适用于分布式系统等特点.测试结果表明系统设计合理,并具有延迟较小的特点,满足分布式系统的要求.     

Real-time support in multihop wireless networks

Personal communications and mobile computing will require a wireless network infrastructure which is fast deployable, possibly multihop, and capable of multimedia service support. The first infrastructure of this type was the Packet Radio Network (PRNET), developed in the 70's to address the battlefield and disaster recovery communication requirements. PRNET was totally asynchronous and was based on a completely distributed architecture. It handled datagram traffic reasonably well, but did not offer efficient multimedia support. Recently, under the WAMIS (Wireless Adaptive Mobile Information Systems) and Glomo ARPA programs several mobile, multimedia, multihop (M³) wireless network architectures have been developed, which assume some form of synchronous, time division infrastructure. The synchronous time frame leads to efficient multimedia support implementations. However, it introduces more complexity and is less robust in the face of mobility and channel fading. In this paper, we examine the impact of synchronization on wireless M³ network performance. First, we introduce MACA/PR, an asynchronous network based on the collision avoidance MAC scheme employed in the IEEE 802.11 standard. Then, we evaluate and compare several wireless packet networks ranging from the totally asynchronous PRNET to the synchronized cluster TDMA network. We examine the tradeoffs between time synchronization and performance in various traffic and mobility environments.     

Multiple-access interference processes are self-similar in multimedia CDMA cellular networks

We consider bursty data communications in code-division multiple-access (CDMA) cellular networks. The significant fluctuation of the cochannel multiple-access interference (MAI) in such systems makes it very challenging to carry out radio resource management. A main goal of this paper is to obtain a fundamental understanding of the temporal correlation structure of the MAI, which plays a crucial role in effective resource allocation. To this end, we take a cross-layer design approach, and characterize the stochastic MAI process while taking into account both the burstiness of data traffic and time-varying channel conditions. Our main results reveal that under standard assumptions on ON/OFF traffic flows and fading channels, the MAI process exhibits scale-invariant burstiness and is "self-similar" (with Hurst parameter 1/2相似文献   

IMS多媒体会议业务实现方案研究

本文对IMS多媒体会议业务的协议进展,平台系统架构及网元设置方案等进行了研究,对未来的平台部署提出了方案构想.     

High-performance architectures for IP-based multihop 802.11 networks

The concept of a forwarding node, which receives packets from upstream nodes and then transmits these packets to downstream nodes, is a key element of any multihop network, wired or wireless. While high-speed IP router architectures have been extensively studied for wired networks, the concept of a "wireless IP router" has not been addressed so far. We examine the limitations of the IEEE 802.11 MAC protocol in supporting a low-latency and high-throughput IP datapath comprising multiple wireless LAN hops. We first propose a wireless IP forwarding architecture that uses MPLS with modifications to 802.11 MAC to significantly improve packet forwarding efficiency. We then study further enhancements to 802.11 MAC that improve system throughput by allowing a larger number of concurrent packet transmissions in multihop 802.11-based IP networks. With 802.11 poised to be the dominant technology for wireless LANs, we believe a combined approach to MAC, packet forwarding, and transport layer protocols is needed to make high-performance multihop 802.11 networks practically viable.