Reed-Solomon码在MPEG-4视频流传输中的应用

本文以MPEG-4视频流作为研究的载体,详细研究基于Reed-Solomon码前向错误保护(FEC)的差错控制,实现了网络传输中的丢包恢复,并通过对算法的改进大大提高了编解码的运算速度。实验结果表明使用FEC机制可以有效提高视频传输的质量。     

TD—MBMS技术及其组网分析

随着移动通信网络的技术发展和用户业务需求的多样化,用户希望通过移动无线网络体验多媒体广播组播业务的需求日益明显,例如手机电视、天气预报、新闻和杂志等业务。多媒体广播组播业务的特点在于所需传输带宽高,占用大量无线资源;面向服务的用户数多,不仅仅针对个别用户。无线蜂窝网络中通常采用点到点的专用信道方式提供业务,     

NEWTEC 卫星IP加速器PEP-Box 3000介绍

卫星IP加速器、TCP/IP加速、数据压缩/加密、多种业务不同优先及控制、可加速的VPN通过卫星和移动网络来访问公共IP网络已经日益被私人和企业用户所接受,并日益成为运营商的主要业务之一。但是,TCP和HTTP这两个在Internet上应用最广泛的协议,在像卫星网络这类高延时、高丢包率的系统中却只能提供非常低的传输效率,用户只能得到非常低     

基于机会式网络编码的低时延广播传输算法

为了提高无线网络中数据包广播传输的效率,本文提出了一种基于机会式网络编码的广播传输算法.该算法在发送端按一定顺序选择不同终端的丢包,并采用异或运算编码重传包,在终端采用从重传包中解码数据包的方法恢复丢包.该算法优先恢复时间重要性较高的丢包,并使多个终端同时从单个重传包恢复其丢包,因此有效地提高了广播传输效率并降低了传输...     

移动IP网络承载实时业务的4个关键

移动IP网络毕竟是一项新的技术及应用,特别在对实时业务的承载上,有其独有的特色。不同的业务有着不同的业务要求,具体体现在速率、时延、时延抖动以及丢包率等方面。从IP网络的角度,一般采用QoS来区分不同的业务需求。业界第一个实现移动网络下采用IP机制承载实时业务的cdma2000 1XEV-DO RevA网络,是一个端到端有QoS保证的网络,对用户的QoS有严格的定义和分类,有用户间的QoS定义、用户内不同业务QoS的定义以及对应不同的数据流的定义。     

FEC在3G多媒体实时传输系统中的应用

3G无线传输是多媒体实时传输的新方式,比传统方式更加灵活、便捷。为了克服在3G无线网络传输中的数据丢包问题,提出了利用FEC和交织来提高数据传输正确率的方法,主要研究了交织和RS(204,188)纠错码的在3G传输系统中的设计和实现,最后对整个系统在不同丢包率信道下的性能进行了对比测试。     

FEC在高波动性网络中的应用研究

前向纠错(FEC)方式可以有效提高网络数据传输的可靠性。喷泉码(Digital Fountain)作为其中较先进的一种,在数字视频广播(DVB)和网络通信等领域有着广泛的应用。设计了RS码和Raptor码的性能实验,验证在较高丢包率下的解码性能。提出了结合重传机制的Raptor码多路传输方案。实验证明,对于高波动性网络中的UDP传输,使用Raptor码能以较低的解码开销获得稳定的解码成功率,而ARQ-Raptor多路传输方案能有效地利用多路带宽进行可靠的数据传输。     

OBS网络中基于优先级抢占的恢复机制

提出一种新的支持光突发交换网络中优先级抢占的快速恢复机制.该机制对不同优先级的业务采取不同的恢复策略,实现故障的快速恢复.同时采用阈值检测方式支持优先级抢占,减少受影响链路中较高优先级业务的丢包.仿真结果表明,基于优先级抢占的恢复机制具有较低的丢包率,对高优先级业务丢包率性能改善更为明显.     

FEC在高波动性网络中的应用研究北大核心

前向纠错(FEC)方式可以有效提高网络数据传输的可靠性。喷泉码(Digital Fountain)作为其中较先进的一种,在数字视频广播(DVB)和网络通信等领域有着广泛的应用。设计了RS码和Raptor码的性能实验,验证在较高丢包率下的解码性能。提出了结合重传机制的Raptor码多路传输方案。实验证明,对于高波动性网络中的UDP传输,使用Raptor码能以较低的解码开销获得稳定的解码成功率,而ARQ-Raptor多路传输方案能有效地利用多路带宽进行可靠的数据传输。     

基于多门限预留机制的自适应带宽分配算法

针对异构无线网络融合环境提出了一种基于多门限预留机制的自适应带宽分配算法,从而为多业务提供QoS保证。该算法采用多宿主传输机制,通过预设各个网络中不同业务的带宽分配门限,并基于各个网络中不同业务和用户的带宽分配矩阵,根据业务k支持的传输速率等级需求和网络状态的变化,将自适应带宽分配问题转化为一个动态优化问题并采用迭代方法来求解,在得到各个网络中不同业务和用户优化的带宽分配矩阵的同时,在带宽预留门限和网络容量的约束条件下实现网络实时吞吐量的最大化,以提高整个异构网络带宽的利用效率。数值仿真结果显示,所提算法能够支持满足QoS需求的传输速率等级,减小了新用户接入异构网络的阻塞概率,提高了平均用户接入率并将网络吞吐量最大提高40%。     

基于CATV网的可靠多播机制研究

针对CATV网的带宽优势,提出了一种面向CATV网的IP多播流分发服务机制,客户端通过DVB卡分层接收流式文件,并利用IP网作为回传链路。该方案解决了单向广播网无法回传丢包及网络服务情况的问题,对于网络的突发性长时间丢包具有一定的稳健性。仿真结果显示该方案可靠性强,扩展性好,特别适合具有较多接收者的视频流分发。     

无线网络中基于机会网络编码的加权广播重传

在无线广播网链路状态不同和丢包率高的条件下,基于机会网络编码的数据分发策略面临传输效率低和计算复杂度高的问题。针对这一问题,该文提出一种新的基于机会网络编码的加权广播重传(Weighted Opportunistic Network Coding Retransmission, WONCR)方案。该方案通过构建加权数据包分布矩阵(Weighted Packet Distribution Matrix, WPDM),在重传过程中采用新的调度算法进行编码数据包的选取,并将选取的数据包进行XOR编码后再重传。机会仿真结果表明,WONCR方案提高了传输效率,且计算开销较小,实现了无线广播网中高效、可靠的数据分发。     

Reliable packet transmissions in multipath routed wireless networks

We study the problem of using path diversification to provide low probability of packet loss (PPL) in wireless networks. Path diversification uses erasure codes and multiple paths in the network to transmit packets. The source uses Forward Error Correction (FEC) to encode each packet into multiple fragments and transmits the fragments to the destination using multiple disjoint paths. The source uses a load balancing algorithm to determine how many fragments should be transmitted on each path. The destination can reconstruct the packet if it receives a number of fragments equal to or higher than the number of fragments in the original packet. We study the load balancing algorithm in two general cases. In the first case, we assume that no knowledge of the performance along the paths is available at the source. In such a case, the source decomposes traffic uniformly among the paths; we call this case blind load balancing. We show that for low PPL, blind load balancing outperforms single-path transmission. In the second case, we assume that a feedback mechanism periodically provides the source with information about the performance along each path. With that information, the source can optimally distribute the fragments. We show how to distribute the fragments for minimized PPL, and maximized efficiency given a bound on PPL. We evaluate the performance of the scheme through numerical simulations.     

A hybrid network coding technique for single-hop wireless networks

In this paper, we investigate a hybrid network coding technique to be used at a wireless base station (BS) or access point (AP) to increase the throughput efficiency of single-hop wireless networks. Traditionally, to provide reliability, lost packets from different flows (applications) are retransmitted separately, leading to inefficient use of wireless bandwidth. Using the proposed hybrid network coding approach, the BS encodes these lost packets, possibly from different flows together before broadcasting them to all wireless users. In this way, multiple wireless receivers can recover their lost packets simultaneously with a single transmission from the BS. Furthermore, simulations and theoretical analysis showed that when used in conjunction with an appropriate channel coding technique under typical channel conditions, this approach can increase the throughput efficiency up to 3.5 times over the automatic repeat request (ARQ), and up to 1.5 times over the HARQ techniques.     

Efficient broadcasting protocols for regular wireless sensor networks

The wireless sensor network (WSN) has attracted lots of attention recently. Broadcast is a fundamental operation for all kinds of networks and it has not been addressed seriously in the WSN. Therefore, we propose two types of power and time efficient broadcasting protocols, namely one‐to‐all and all‐to‐all broadcasting protocols, for five different WSN topologies. Our one‐to‐all broadcasting protocols conserve power and time by choosing as few relay nodes as possible to scatter packets to the whole network. Besides, collisions are carefully handled such that our one‐to‐all broadcasting protocols can achieve 100% reachability. By assigning each node a proper channel, our all‐to‐all broadcasting protocols are collision free and efficient. Numerical evaluation results compare the performance of the five topologies and show that our broadcasting protocols are power and time efficient. Copyright © 2005 John Wiley & Sons, Ltd.     

移动Ad Hoc网络中一种分布式QoS保证的多址接入协议

基于随机竞争和冲突解决的思想,本文为多跳移动Ad Hoc网络提出了一种分布式服务质量(QoS)保证的多址接入(QMA)协议.该协议中,节点在发送业务分组前利用预报突发进行竞争接入,节点根据业务分组时延情况和最早失效优先原则确定预报突发的长度,所发预报突发能持续到最后的节点优先获得接入.同时,具有实时业务的节点可以按照其优先级在更早的竞争微时隙中开始发送预报突发,而有非实时业务的节点只能在前面竞争微时隙空闲的情况下,才能在后面的微时隙开始发送预报突发,因此发送实时业务的节点可以比发送非实时业务的节点更优先接入信道,从而在移动Ad Hoc网络中实现了对多媒体业务的QoS保证.最后利用OPNET仿真评估了QMA协议的多址性能,并与IEEE 802.11e协议的性能做了比较,结果表明QMA协议可以提供较高的吞吐量和较低的实时业务时延.     

Buffering management schemes for optical variable length packets under limited packet sorting

This paper studies several buffering strategies for optical packet switching (OPS) under limited packet sorting. Three schemes, which are able to sort newly arrived packets based on packet’s length as well as capability of finding the minimum buffer occupancy, are analyzed and compared. Results show that all three proposed schemes could improve OPS performance considerably in terms of probability of packet loss (PPL) and probability of information loss (PIL). In addition, the simulation results show that not all the newly arrived packets need to be sorted in order to obtain minimum packet loss probability. Since the amount of packets and thus the packet processing time is significant in OPS, it is possible that not all the packets can be processed using one of the buffering strategies. An important finding of this paper is that if only 10% of the packets are sorted, the PPL is comparable to the minimum packet loss value obtained when 100% of the packets are sorted.     

Throughput-Delay Performance of Interconnected CSMA Local Area Networks

The interconnection of two local area networks, each of which connects a large population of users via a carrier-sense multipleaccess (CSMA) channel is considered. In each network, a bridge node receives internetwork packets from the local users and forwards them to the bridge node of the other network via a point-to-point link; the bridge node of the destination network queues these internetwork packets for subsequent broadcasting to the local users. For the multiplexing of the user transmissions and the bridge node transmissions on the available broadcast channel in each network, frequency division, and contention are considered. The throughput-delay characteristics of the interconnected system operating under the above multiplexing techniques are found and comparisons are made. It is shown that contention multiplexing can yield system performance comparable to that of frequency division multiplexing, while requiring no hardware or software modification of either network in the interconnected system.     

A secure wireless mission critical networking system for unmanned aerial vehicle communications

A privacy-preserving secure communication in ad hoc (without infrastructure) mission critical wireless networking system suitable for unmanned aerial vehicle communication systems is introduced and analyzed. It is expected that in a critical condition, few ad hoc (without infrastructure) mission critical wireless networking systems will work together. To make the simple and low cost privacy-preserving secure communication among the same network, each transmitting mobile node generates packets in such a way that its wanted receiving mobile nodes can read the message packets easily. On the other hand, the unwanted receiving mobile nodes from other networks cannot read those message packets. In addition, the unwanted receiving mobile nodes receive ‘jamming packets’ if they try to read them. This mechanism prevents the malicious receivers (readers from other networks) from reading the packets and obtaining information from this network. Results show that the throughput is very high and does not detect any jamming packets, if the receiving nodes of a network try to read packets transmitted by the nodes from the same networks.     

Modeling of OpenFlow-related handover messages in mobile networks

Software defined networking (SDN) and its most popular southbound implementation OpenFlow (OF) are already greatly exploited in the existing mobile cellular networks as part of data centers and mobile core networks. Due to user’s mobility, it is of upmost importance for the operators to provide the shortest possible interruption when the mobile users are performing the procedure of handover. In this work, we proposed a novel analytical approach to model the OF-related handover messages exchanged between the OF-switches and the SDN controller. We modeled two different OF-switch implementations and we compared the results: (1) single shared buffer used for the control and data plane; (2) two priority buffers, where the data plane packets are served only when there are no packets to be processed in the control plane. We numerically evaluated the two systems and we validated the model by using simulations. The obtained results clearly point that although the priority buffering increased the complexity, it effectively provided the shortest handover delay. Therefore, the priority buffering should be the preferred mechanism for mobile networks.