无线Mesh网中编码感知组播路由协议CAMR

网络编码是一种能够提高网络吞吐量的新技术,将网络编码应用于无线Mesh网组播对Mesh网络进一步实用化有重要意义.编码感知路由是一种能够充分识别和利用网络中的编码机会的路由.虽然已有若干个基于网络编码的单播路由协议,但无线网络中编码机会并没有被充分利用,到目前为止还没有无线Mesh网络中的编码感知组播路由协议.提出一个编码感知组播路由协议CAMR(coding-aware multicast routing).CAMR协议利用了一个新奇的编码感知路由度量CAM(coding-awarerouting metric),可以度量无线Mesh网络中节点的实际编码机会和编码能力的大小.基于CAM设计的CAMR协议可以充分利用无线Mesh网络中节点的编码机会,提高了无线Mesh网络组播的吞吐量.模拟实验验证了CAMR协议的优势及其有效性.     

多播路由在无线网络中的OPNET建模与性能测试

多播路由技术凭借其有效节省网络带宽的优势,已成为研究无线多媒体网络服务质量(QoS)的热点内容。其中协议独立多播稀疏模式(PIM-SM)是域内多播路由协议中常见的协议。使用OPNET平台进行基于IEEE802.11无线局域网的仿真实验,首先对单播路由和PIM-SM多播路由在吞吐量上进行比较,实验结果表明多播路由在带宽的利用率上具有明显的优势。然后对文件传输、数据库访问、网络电话和视频会议等多媒体业务,进行单播路由和PIM-SM多播路由对比仿真实验,并且从延迟、延迟抖动和丢包率等方面给出结论,为真实无线多媒体网络环境的搭建提供一个很好的参考。     

组播协议在OPNET中的建模与仿真

该文以IP组播技术为重点,结合网络仿真软件OPENT Modeler,分析该软件环境下IP组播网络的建模机制,包括参考标准、组的管理、支持的应用、组播路由协议的选择,节点加入组播组与发送源发送组播数据的流程。以校园网视频会议和FTP传输应用为例,构建网络仿真模型,一方面比较单播与组播方式下的网络性能,分析了视频流量的发送情况、视频会议分组的端到端延时,FTP传输的响应时间,骨干网络点到点链路吞吐量;另一方面比较了组播方式采用共享树机制和由共享树切换到最短路径树在网络性能上的改进,包括分组延迟的降低、汇合点路由器上拥塞发生的减少等。同时,也对无线移动通信网络环境下的组播技术提出更多需要考虑的因素。     

基于组播通信的交通通信网络研究

研究交通通信网络,提高网络的吞吐量和数据传输效率。针对传统的单播组网中通信发送者需要多次复制相同的数据包以满足多个接受者同时提出的数据请求,随着数据请求的增多使得发送者的通信负担加重,造成网络拥塞、吞吐量不高的问题。为了解决上述难题,提出基于组播通信的交通通信网络的组网方法。采用Mesh结构构建交通通信网络的组播模型,使得网络节点之间建立有线或无线的连接,然后利用网络编码算法实现网络间的通信,使得源点只需发送一次就可向多个终点成功传输相同的数据。实验表明,组网方法能够有效解决数据请求过多时网络吞吐量不高的问题,同时提高了数据传输的效率,取得了满意的结果。     

Design of a Scalable Multicast Scheme With an Application-Network Cross-Layer Approach

This paper develops an efficient and scalable multicast scheme for high-quality multimedia distribution. The traditional IP multicast, a pure network-layer solution, is bandwidth efficient in data delivery but not scalable in managing the multicast tree. The more recent overlay multicast establishes the data-dissemination structure at the application layer; however, it induces redundant traffic at the network layer. We propose an application-oriented multicast (AOM) protocol, which exploits the application-network cross-layer design. With AOM, each packet carries explicit destinations information, instead of an implicit group address, to facilitate the multicast data delivery; each router leverages the unicast IP routing table to determine necessary multicast copies and next-hop interfaces. In our design, all the multicast membership and addressing information traversing the network is encoded with bloom filters for low storage and bandwidth overhead. We theoretically prove that the AOM service model is loop-free and incurs no redundant traffic. The false positive performance of the bloom filter implementation is also analyzed. Moreover, we show that the AOM protocol is a generic design, applicable for both intra-domain and inter-domain scenarios with either symmetric or asymmetric routing.     

Optimal opportunistic routing and network coding for bidirectional wireless flows

There is growing interest in recent years in routing methods for wireless networks that leverage the broadcast nature of the wireless medium and the ability of nodes to overhear their neighbors’ transmissions. Such methods include opportunistic routing (OR), which generally choose the next hop on a routing path only after the outcome of the previous transmission is known; and wireless network coding (NC), which linearly combines packets from different flows coexisting in the network. In this paper, we study the potential benefits of forwarding schemes that combine elements from both the OR and NC approaches, when traffic on a bidirectional unicast connection between two nodes is relayed by multiple common neighbors. We present a theoretically optimal scheme that provides a lower bound on the expected number of transmissions required to communicate a packet in both directions as a function of link error probabilities, and demonstrate that this bound can be up to 20% lower than with either OR or NC employed alone even in a small network. Using simulation, we further explore the control overhead in a direct implementation of the scheme with a simple coordination mechanism and show that the optimal bound can be closely approached for a wide range of link error rates.     

一种基于网络编码的无线网络机会路由算法

机会路由和网络编码是近几年出现的两项新技术,它们能使有损网络达到较高的吞吐量.然而,已有的研究两者大多是分离的,这样不能同时发挥两者的优势.提出了一种基于网络编码的无线网络机会路由算法- MinACK( Minimum ACKnowledgement),它结合了机会路由和网络编码各自的优势,能够在网络中同时传输多个段的...     

TCP-aware network coding with opportunistic scheduling in wireless mobile ad hoc networks

This paper presents a scheme that employs TCP-aware network coding with opportunistic scheduling to enhance TCP throughput in wireless mobile ad hoc networks. Specifically, it considers a TCP parameter, congestion window size, and wireless channel conditions simultaneously to improve TCP throughput performance. Evaluation of this scheme is carried out by using ns2 simulations in different scenarios. The results show that the proposed scheme gives approximately 35% throughput improvement in a high mobility environment and about 33% throughput increase in no or low mobility environment as compared to traditional network coding with opportunistic scheduling. This paper also proposes a new adaptive-W (i.e., adaptive Waiting time) scheme whose objective is to adaptively control waiting time of overheard packets that are stored in a buffer to achieve tradeoff between throughput and overhead.     

Dynamic retransmission control for reliable mobile multicast

Most existing multicast protocols adopt a static retransmission scheme(unicast or multicast) to retransmit lost packets.In the mobile multicast environment,static multicast retransmission mode may lead to congestion in the receivers‘ wireless interfaces,while static unicast mode may result in great network load.Both static unicast and multicast retransmission modes will cause a performance loss.This paper logically divides the mobile multicast network into fixed and mobile parts,and focuses on the mobile part.Then this paper analyzes the retransmission costs when multicast or unicast mode is chosen.Two main parameters are used to compare their efficiencies:the average air-interface utilization of each receiver and the average network load.Based on the results of analysis,two new algorithms,called NLPA(Network Load Priority Algorithm)and AUPA(Air-interface Utilization Priority Algorithm)are presented.Finally,simulation results conclude that,with proper parameters,both NLPA and AUPA can dynamically alternate between unicast and multicast retransmission modes acording to the conditions of network and receiver,and avoid congestion in receivers‘ wireless interfaces as well as great network load,with a better use of network and terminal resources.     

低开销的无线网络编码机会路由协议设计

针对基于无线Mesh网络编码的机会路由协议的节点转发冗余问题,从线性空间的角度对该类协议的信息传输过程进行建模与分析,提出一种基于动态冗余控制的无线Mesh网络编码机会路由协议。该协议利用零空间确认技术估计各节点的更新信息总量,根据更新总量动态调整节点转发冗余,通过引入转发优先级调度机制,避免不同的转发节点重复转发来自于相同线性空间的编码包。仿真实验结果显示,与经典的MORE协议相比,该协议能提高30％-100％的网络吞吐量,同时降低20％-45％的归一化开销。     

Fundamental limits on end-to-end throughput of network coding in multi-rate and multicast wireless networks

This paper investigates the interaction between network coding and link-layer transmission rate diversity in multi-hop wireless networks. By appropriately mixing data packets at intermediate nodes, network coding allows a single multicast flow to achieve higher throughput to a set of receivers. Broadcast applications can also exploit link-layer rate diversity, whereby individual nodes can transmit at faster rates at the expense of corresponding smaller coverage area. We first demonstrate how combining rate-diversity with network coding can provide a larger capacity for data dissemination of a single multicast flow, and how consideration of rate diversity is critical for maximizing system throughput. Next we address the following question: given a specific topology of wireless nodes, what is the maximum rate that can be supported by the resultant network exploiting both network coding and multi-rate? We present a linear programming model to compute the maximal throughput that a multicast application can achieve with network coding in a rate-diverse wireless network. We also present analytical results where we observe noticeably better throughput than traditional routing. This suggests there is opportunity for achieving higher throughput by combining network coding and multi-rate diversity.     

Fast reroute from single link and single node failures for IP multicast

The rise in multicast implementations has seen with it an increased support for fast failure recovery from link and node failures. Most recovery mechanisms augment additional services to existing protocols causing excessive overhead, and these modifications are predominantly protocol-specific. In this paper, we develop a multicast failure recovery mechanism that constructs protocol independent fast reroute paths to recover from single link and single node failures. We observe that single link failure recovery in multicast networks is similar to recovering unicast traffic, and we use existing unicast recovery mechanisms for multicast traffic. We construct multicast protection trees that provide instantaneous failure recovery from single node failures. For a given node x, the multicast protection tree spans all its neighbors and does not include itself. Thus, when the node fails, the neighbors of the node are connected through the multicast protection tree instead of node x, and forward the traffic over the multicast protection tree for the duration of failure recovery. The multicast protection trees are constructed a priori, without the knowledge of the multicast traffic in the network. Based on simulations on three realistic network topologies, we observe that the multicast protection trees increase the routing table size only by 38% on average and the path length between any source–destination pair by 13% on average.     

基于干扰感知的无线自组网多播机制

在采用网络编码的无线自组网多播场景中,为了有效地克服节点密度较大时干扰对多播整体性能的影响,提出了一种衡量路径干扰情况的路由度量标准。基于该度量标准,对网络编码机会和节点间干扰避免进行了均衡处理,构建出一种基于部分网络编码的无线自组网干扰感知多播路由机制。仿真结果表明,该机制在能耗、延时和吞吐量等性能方面均优于基于传统网络编码的多播方案,因此特别适用于节点密度较大的场合。     

Reliable and Energy-Efficient Routing for Static Wireless Ad Hoc Networks with Unreliable Links

Energy efficient routing and power control techniques in wireless ad hoc networks have drawn considerable research interests recently. In this paper, we address the problem of energy efficient reliable routing for wireless ad hoc networks in the presence of unreliable communication links or devices or lossy wireless link layers by integrating the power control techniques into the energy efficient routing. We consider both the case when the link layer implements a perfect reliability and the case when the reliability is implemented through the transport layer, e.g., TCP. We study the energy efficient unicast and multicast when the links are unreliable. Subsequently, we study how to perform power control (thus, controlling the reliability of each communication link) such that the unicast routings use the least power when the communication links are unreliable, while the power used by multicast is close to optimum. Extensive simulations have been conducted to study the power consumption, the end-to-end delay, and the network throughput of our proposed protocols compared with existing protocols.     

Cross-layer topology design for network coding based wireless multicasting

This paper considers wireless multicast networks where network coding (NC) is applied to improve network throughput. A novel joint topology and cross-layer design is proposed to maximise the network throughput subject to various quality-of-service constraints, such as: wireless multicast rate, wireless link capacity, energy supply and network lifetime. Specifically, a heuristic NC-based link-controlled routing tree algorithm is developed to reduce the number of required intermediate nodes. The proposed algorithm facilitates the optimisation of the wireless multicast rate, data flow of wireless links, energy supply and lifetime of nodes through a novel cross-layer design. The proposed joint topology and cross-layer design is evaluated and compared against other schemes from the literature. The results show that the proposed scheme can achieve up to 50% increase in the system throughput when compared to a classic approach.     

基于拥塞控制的片上网络多播路由算法

为了满足片上网络日益丰富的应用要求,多播路由机制被应用到片上网络,以弥补传统单播通信方式的不足。以Mesh和Torus类的片上网络为例,分析了基于路径的3种多播路由算法(即XY路由、UpDown路由和SubPartition路由算法),并研究了相应的拥塞控制策略。通过模拟实验表明,多播较单播通信具有更小的平均传输延时和更高的网络吞吐量,且负载分配均匀;特别是SubPartition路由算法随着规模增大效果更加明显;提出的多播拥塞控制机制,能更有效地利用多播通信,提高片上网络的性能。     

Interest-suppression-based NDN live video broadcasting over wireless LAN

Named data networking (NDN) is a new Internet architecture that replaces today’s focus on where – addresses and hosts with what – the content that users and applications care about. One of NDN’s prominent advantages is scalable and efficient content distribution due to its native support of caching and multicast in the network. However, at the last hop to wireless users, often the WiFi link, current NDN implementation still treats the communication as multiple unicast sessions, which will cause duplicate packets and waste of bandwidth when multiple users request for the same popular content. WiFi’s built-in broadcast mechanism can alleviate this problem, but it suffers from packet loss since there is no MAC-layer acknowledgement as in unicast. In this paper, we develop a new NDN-based cross-layer approach called NLB for efficient and scalable live video streaming over wireless LAN. The core ideas are: using WiFi’s broadcast channel to deliver content from the access point to the users, a leader-based mechanism to suppress duplicate requests from users, and receiver-driven rate control and loss recovery. The design is implemented and evaluated in a physical testbed comprised of one software AP and 20 Raspberry Pi-based WiFi clients. While NDN with multiple unicast sessions or plain broadcast can support no more than ten concurrent viewers of a 1Mbps streaming video, NDN plus NLB supports all 20 viewers, and Received December 29, 2015; accepted April 28, 2016 E-mail: zhxp@tsinghua.edu.cn can likely support much more when present.     

无线Mesh 网络低干扰组播

不同于无线传感器网络和移动Ad Hoc网络,无线Mesh网络中的组播主要侧重于提高吞吐量,而干扰是影响吞吐量的重要因素。在构建组播拓扑时,传统的方法主要考虑最小价值或最短路径,而通过减少干扰来提高组播性能的研究较少,且它们的干扰计算方法都采用单播的思想,并不适合于组播。例如,当n个接收节点同时从一个节点接收数据时,在组播中这n个接收节点之间不存在干扰,而在单播中认为存在干扰。因此,提出了组播冲突图来计算组播干扰,给出组播树干扰的定义。可以发现,求最小干扰组播扰树是NP完全问题,然后提出基于万有引力的启发式算法构建具有较小干扰的组播树。为了适用于多信道的情况,提出了满足不同干扰范围的多跳信道分配算法。最后,仿真结果显示,与MCM相比,所提出的算法无论是在单天线单信道还是多天线多信道下,都能取得较高的吞吐量和较低的延迟。     

Testbed results of an opportunistic routing for multi-robot wireless networks

Opportunistic routing is a candidate for multihop wireless routing where the network topology and radio channels vary rapidly. However, there are not many opportunistic routing algorithms that can be implemented in a real multihop wireless network while exploiting the node mobility. It motivates us to implement an opportunistic routing, random basketball routing (BR), in a real multi-robot network to see if it can enhance the capacity of the multihop network as mobility increases. For implementation purposes, we added some features, such as destination RSSI measuring, a loop-free procedure and distributed relay probability updating, to the original BR. We carried out the experiments on a real multi-robot network and compared BR with AODV combined with CSMA/CA (routing + MAC protocol). We considered both static and dynamic scenarios. Our experiments are encouraging in that BR outperforms AODV + CSMA/CA, particularly in dynamic cases; the throughput of BR is 6.6 times higher than that of AODV + CSMA/CA. BR with dynamic networks shows 1.4 times higher throughput performance than BR with static networks. We investigate the performance of BR in the large-scale network using NS-2 simulation. We verify the effect of node density, speed, destination beacon signal and loop-free procedure. According to the large-scale simulation, the end-to-end throughput grows with the node speed.     

Routing Internet traffic in heterogeneous mesh networks: Analysis and algorithms

In practical wireless mesh networks (WMNs), gateways are subject to hard capacity limits on the aggregate number of flows (in terms of bit rate) that they can support. Thus, if traffic is routed in the mesh network without considering those constraints, as well as the traffic distribution, some gateways or intermediate mesh routers may rapidly get overloaded, and the network resources can be unevenly utilized. To address this problem, in this paper we firstly develop a multi-class queuing network model to analyze feasible throughput allocations, as well as average end-to-end delay, in heterogeneous WMNs. Guided by our analysis, we design a Capacity-Aware Route Selection algorithm (CARS), which allocates network paths to downstream and upstream Internet flows so as to ensure a more balanced utilization of wireless network resources and gateways’ fixed connections. Through simulations in a number of different network scenarios we show that the CARS scheme significantly outperforms conventional shortest path routing, as well as an alternative routing method that distributes the traffic load on the gateway nodes to minimize its variance.