机会网络视频数据的分块渐进传输新方法

各类移动多媒体智能终端的普及使得设备间的自组织机会通信成为国际研究热点,而移动节点间的机会通信方式已无法满足日益增长的多媒体传输需求.面向机会组网与视频内容传输问题,基于机会网络实际通信能力计算,提出了一种视频分块大小最优化计算方法,使机会网络通信能力得到最大化利用;提出了一种能够实现渐进式接收视频分块的路由调度算法,建立分块紧缺度模型,引导分块在目标节点趋于均匀分布.实验结果表明,该方法能在恶劣通信环境下实现高效的视频数据预览与传输,可为相关视频内容的无线移动传输提供支持.     

无线多跳网络中一种基于网络编码的机会路由

近年来机会路由和网络编码是两种利用无线信道广播特性提高网络性能的新兴技术。相比传统的静态路由决策,机会路由利用动态和机会路由选择减轻无线有损链路带来的影响。网络编码可以提高网络的资源利用率。但编码机会依赖于多个并发流所选路径的相对结构。为了创造更多的网络编码机会和提高网络吞吐量,本文提出了一种基于流间网络编码的机会路由(ORNC)算法。在ORNC中,每个分组转发的机会路径选择是基于网络编码感知的方式进行的。当没有编码机会时,采用背压策略选择下一跳转发路径以平衡网络负载。仿真结果表明本文提出的ORNC算法能够提高无线多跳网络的吞吐量。     

无线多跳网络中机会路由效率增强研究(英文)

Opportunistic routing(OR) is an effective way to guarantee transmission reliability in wireless multi-hop networks.However,little research focuses on transmission efficiency.Thus,an analytical model based on open queuing network with Markov chains was proposed to evaluate the efficiency.By analyzing two typical ORs,we find duplicate transmission and collision avoidance overhead are the root reasons behind inefficiency.Therefore,a new scheme called dual priority cooperative opportunistic routing(DPCOR) was proposed.In DPCOR,forwarding candidates are configured with dual priority,which enables the network to classify forwarding candidates more effectively so as to reduce the back-off time and obtain more diversity gain.Theoretical analysis and simulation results show DPCOR achieves significant performance improvement with less time overhead compared with traditional routings and typical ORs.     

多优先级业务通信网的阻塞性能分析算法

最短径通信网和多抢占优先级服务方式的研究对于网络规划和减少重载时的业务损失有重要意义。本文利用抢占优先级服务方式的特性和文献［１］的研究结果，建立所研究的具有任意种不同优先级业务最短径通信网的数学模型，导出不同优先级业务通信网点对点阻塞概率的迭代算法，并利用所得到的算法对一个通信网的性能进行了实例分析。本文给出的算法适用于任意多抢占优先级业务下的任意拓扑结构网络。     

机会网络中一种低缓存占用的Epidemic 路由算法

由于机会网络中节点的缓存空间有限,容易导致数据分组丢失和时延增加。针对部分数据分组已经到达目的节点,但是该类分组仍在网络中其它节点存储、传输问题,提出一种低缓存占用的Epidemic路由算法(RBER)。该算法通过SV运算进行节点缓存清理,从而避免这类冗余数据分组对缓存的占用。理论分析和仿真结果表明,该机制能够降低网络开销、数据分组的发送和缓存占用。     

Network coding for multiple unicast sessions in multi-channel/interface wireless networks

Throughput limitation of wireless networks imposes many practical problems as a result of wireless media broadcast nature. The solutions of the problem are mainly categorized in two groups; the use of multiple orthogonal channels and network coding (NC). The networks with multiple orthogonal channels and possibly multiple interfaces can mitigate co-channel interference among nodes. However, efficient assignment of channels to the available network interfaces is a major problem for network designers. Existing heuristic and theoretical work unanimously focused on joint design of channel assignment with the conventional transport/IP/MAC architecture. Furthermore, NC has been a prominent approach to improve the throughput of unicast traffic in wireless multi-hop networks through opportunistic NC. In this paper we seek a collaboration scheme for NC in multi-channel/interface wireless networks, i.e., the integration of NC, routing and channel assignment problem. First, we extend the NC for multiple unicast sessions to involve both COPE-type and a new proposed scheme named as Star-NC. Then, we propose an analytical framework that jointly optimizes the problem of routing, channel assignment and NC. Our theoretical formulation via a linear programming provides a method for finding source–destination routes and utilizing the best choices of different NC schemes to maximize the aggregate throughput. Through this LP, we propose a novel channel assignment algorithm that is aware of both coding opportunities and co-channel interference. Finally, we evaluate our model for various networks, traffic models, routing and coding strategies over coding-oblivious routing.     

无线网络面向视频传输优化的机会网络编码机制

现有的无线网络编码机制大多没有考虑无线链路质量对于视频传输的影响,导致视频质量降低。该文针对这一问题,提出面向视频传输优化的机会网络编码(O2NC)机制。该机制结合网络编码和机会路由技术,根据传输路径收益和视频数据的重要程度计算候选节点集合;同时,考虑视频数据包编码比重和重要程度等参数,评估编码包综合效用,选取转发效用值最大的视频编码组合。仿真结果表明,与典型的网络编码协议相比,O2NC机制能够显著提高视频序列的可解码帧率和峰值信噪比(PSNR)。     

机会网络编码路由协议性能分析与研究

首先引入机会网络的概念以及相应的基础理论知识,包括机会网络的体系结构、通信模式及一些经典的路由协议,然后主要介绍了网络编码的基本概念和原理,重点描述了线性网络编码方法及基于此的高效路由协议,最后对机会网络基于编码路由协议未来发展前景进行了展望。     

Middleman covert channel establishment based on MORE routing protocol using network coding in ad hoc networks

Covert channels have been recently the subject of the study in both creation and countermeasure aspects. There are many different ways to embed the covert data in network standards and protocols, especially in wireless networks. MORE (MAC‐independent opportunistic routing) is an opportunistic routing protocol which uses networks coding to enhance routing performance by reducing the repetitions. This protocol can be a suitable medium for covert channel establishment. A middleman covert channel establishment method is proposed in this paper over MORE routing protocol and with the use of network coding. Hidden data are transferred through packet's payload bytes. Covert sender manipulates coding mechanism by calculating packets' coefficients instead of random selection. The proposed covert channel provides the average throughput of 218 and 231 bps, using two different data length approaches which is relatively a good comparing to the previous network layer covert channels. The proposed covert channel is also a covert storage channel and cannot be removed or restricted. Effect of different network characteristics on the proposed method's capacity and security is investigated by a simulation study, and the results are discussed.     

具有传输成功率保证的概率路由算法的TTL预测模型

概率路由算法是机会网络中一种常用的路由算法,其TTL的设置将直接影响路由的性能.本文首先利用马尔可夫链对概率路由的转发过程进行建模,并从消息的传输成功率和传输延时方面进行性能评估,不仅可以计算出一个消息从源节点到目的节点所需的传输延时,还可以预测出在给定传输成功率下所需要的最短消息生存周期TTL,这对于TTL的设置具有理论上的指导作用.其次,本文建立的预测模型还可以使一些无法到达目的节点的消息及时被删除,从而减少不必要的转发,达到节约网络资源的目的.最后,在两个真实数据集中的实验结果表明,本文提出的模型能够为概率路由中TTL值的准确设置提供有效参考.     

Anti-eavesdropping Network Coding Algorithm Based on T-N Threshold

Catering to the public nature of Ad hoc network in open channel and data communication be-ing easily eavesdropped, this paper proposed an anti-eavesdropping algorithm which is based on network coding. The algorithm is based on the RSA signature algorithm introducing the timestamp and homomorphic mechanism to detect tampering and replay attacks, as the basis for calculating safety, being used as one of measurement in-dicators in router by node safety to establish t pieces of routing entry. It generates encoding vectors by introduc-ing the random number when the source node is encoded and the random number will be divided into n pieces. As long as the sink node receives t pieces of fragments, we can restore the original encoding vector and decode it. If the eavesdropper wiretaps are less than t, they can not get any meaningful information. It is designed for increas-ing the number of linearly independent coded packets.It can improve the decoding efficiency by adopting genera-tional grouping strategy while being encoded. Simulation and theoretical analysis shows that the anti-eavesdropping algorithm based on network coding improves network per-formance and security by coding gain.     

基于网络编码的机会网络高效路由算法

针对采用Epidemic机制的机会网络路由算法在数据分组传送阶段存在通信冗余的问题,提出了一种基于网络编码的高效路由算法--NCBER(network-coding-based epidemic routing）。NCBER在传送数据分组的过程中使用主动异或网络编码和多播,并取消了 Request（请求）控制分组,从而减少数据分组的转发次数和控制分组数量,降低网络开销,缩短分组传输时延。理论分析和仿真结果表明,NCBER 算法在网络开销和数据分组端到端时延性能方面优于经典的Epidemic路由算法及其改进算法MRRMR（message redundancy removal of multi-copy routing）,并且使数据传送成功率保持在100%。     

车联网下基于网络编码的高吞吐量多径路由算法

在车联网中,由于车辆节点间无线链路的频繁中断易导致数据重传,使整个车辆组网性能急剧下降。为此,面向车联网提出了一种增强吞吐量的多径路由算法,其核心是使车辆节点分簇算法支持网络编码,从而达到对乱序和丢失报文恢复的目的。该算法首先采用协同编码通信模型来实现分簇后同簇车辆节点互相协同的多路径传输,然后采用网络编码对源端车辆和中间车辆节点发送的数据进行线性编码操作,最后在目的端节点予以解码。在基于QualNet仿真平台上的实验结果表明,该算法能够有效地提升车联网中多径路由的吞吐量。     

无线传感器网络中基于最优转发集的协作式编码传输协议

针对当前大多数据传输协议没有充分利用无线信道的广播特性这一问题,本文提出了基于网络编码的机会路由协议NCOR（Network Coding based Opportunistic Routing protocol）.首先,通过分析网络端到端传输代价,本文提出了最优转发集构造机制以最小化传输代价.此后,NCOR在转发集内执行节点协作式编码传输以保证传输可靠性.最后,理论分析了NCOR的传输可靠性结论.仿真实验表明NCOR可适用于不同的链路环境,且在保证可靠传输的同时,大幅降低了网络能耗.     

移动自组网中基于部分网络编码的机会主义路由

完全网络编码可用以解决机会主义路由中空间重用及重复报文问题,但增大了报文平均延迟,且报文数据流表现出突发性特征,不利于目标节点解码.本文针对移动自组网提出基于部分网络编码的机会主义路由OR-PNC,采用任意长度部分网络编码方式对报文编码.实验表明OR-PNC可有效降低报文平均延迟达26%,目标节点应用层原始报文到达流更均衡.     

Performance modeling of data transmission by using random linear network coding in DTNs

In Delay Tolerant Networks (DTNs), mobile nodes exploit encounter chances to transmit data via the established opportunistic link between encounter nodes. The transmission capacity between two encounter nodes is constrained by the duration of opportunistic links. How to transmit data efficiently is one of the fundamental and most important issues in DTNs. Recently, Random Linear Network Coding (RLNC) is proposed as a promising approach to improve data transmission efficiency in DTNs. To facilitate the development of deployment of RLNC based routing protocols, it is imperative to quantify the performance gain brought by RLNC in a rigorous and systematic way. In this paper, we develop an analytical model to evaluate the data transmission performance of RLNC based epidemic routing in DTNs. In the model, we consider that multiple unicast communication sessions compete for limited \capacity. Numerical results validate the effectiveness of our analytical model and demonstrate the significant performance improvement for data transmission in DTNs brought by RLNC. Our work of this paper provides a general tool for performance evaluation and useful guidelines for designing RLNC based routing protocols in DTNs. Copyright © 2015 John Wiley & Sons, Ltd.     

On selection of forwarding nodes for long opportunistic routes

Opportunistic routing is a promising routing paradigm which increases the network throughput. It forces the sender’s neighbors, who successfully overheard the transmitted packet, to participate in the packet forwarding process as intermediate forwarding nodes. As a seminal opportunistic routing protocol, MORE combines network coding idea with opportunistic routing to eliminate the need for strict coordination among active forwarding nodes. In this paper, we show that MORE performance does not scale well with the route length, especially when the route length goes beyond two hops. Also, we found that MORE fails to establish a working opportunistic route in sparse networks. Clearly, the network throughput is directly influenced by both the quantity and quality of forwarding nodes, and their cooperation order. In this paper, we propose a new forwarder selection mechanism which considers the route length, link qualities, the distance from the source, and nodes density. It eliminates the occasional route disconnectivity happening in MORE and improves the quality of the established opportunistic routes. The simulation result indicates that our proposal always outperforms MORE when dealing with long opportunistic routes.

     

Network coding-aware flow control in wireless ad-hoc networks with multi-path routing

In this paper, we study a flow control problem considering network coding in wireless ad-hoc networks with multi-path routing. As a network coding scheme, we use XOR network coding, in which each node bitwise-XORs some packets received from different sessions, and then broadcasts this coded packet to multiple nodes in a single transmission. This process can reduce the number of required transmissions, and thus can improve network utilization, especially if it is used with appropriate network coding-aware protocols. Considering this XOR network coding, we formulate an optimization problem for flow control that aims at maximizing network utility. By solving the optimization problem in a distributed manner, we implement a distributed flow control algorithm that provides the optimal transmitting rate on each of multiple paths of each session. The simulation results show that our flow control algorithm performs well exploiting the advantages of network coding and provides significant performance improvement.     

Optimum node placement in wireless opportunistic routing networks

In recent years there has been a growing interest in opportunistic routing as a way to increase the capacity of wireless networks by exploiting its broadcast nature. In contrast to traditional uni-path routing, in opportunistic routing the nodes overhearing neighbor’s transmissions can become candidates to forward the packets towards the destination.In this paper we address the question: What is the maximum performance that can be obtained using opportunistic routing? To answer this question we use an analytical model that allows to compute the optimal position of the nodes, such that the progress towards the destination is maximized. We use this model to compute bounds to the minimum expected number of transmissions that can be achieved in a network using opportunistic routing.     

Transmitting time‐critical data over heterogeneous subnetworks using standardized protocols

Current communication networks consist of subnetworks of different types. Therefore a common network protocol has to be used for the transmission of data in such a heterogeneous network. Since some time the requirement of mobility in communication networks is showing up. For that reason wireless networks are playing an increasing role as subnetworks. On the other hand there is the need for multiplexed transmission of time-critical and non time-critical (normal) data within a heterogeneous network. In this paper we discuss the problem of multiplexed transmission of time-critical and of non time-critical data over a wireless type subnetwork using a common standardized network protocol. Many of the available wireless subnetworks are of low or medium transmission speed and guarantee a fixed transmission bandwidth at the access point. We describe a mechanism to transmit time-critical data in such a type of subnetwork using a connectionless transport and a connectionless network protocol. The concurrent transmission of non time-critical data using a connection oriented transport and the same connectionless network protocol is assumed to be of lower priority; it is scheduled in a way to fill the remaining capacity, which has not been reserved for the transmission of time-critical data. In our discussion we concentrate on the standardized ISO/OSI protocools CLNP as connectionless network protocol, CLTP as connectionless transport protocol and TP4 as connection oriented transport protocol. We propose a header compression protocol and a fragmentation protocol for use on low bandwidth subnetworks. This revised version was published online in June 2006 with corrections to the Cover Date.