移动自组织网络中基于树结构的优化组播路由算法(英)

Mobile Ad hoc Networks(MANETs) play an important role in emergency communications where network needs to be constructed temporarily and quickly.Since the nodes move randomly,routing protocols must be highly effective and reliable to guarantee successful packet delivery.Based on the data delivery structure,most of the existing multicast routing protocols can be classified into two folders:tree-based and mesh-based.We observe that tree-based ones have high forwarding efficiency and low consumptions of bandwidth,and they may have poor robustness because only one link exists between two nodes.As a treebased multicast routing protocol,MAODV(Multicast Ad hoc On-demand Vector) shows an excellent performance in lightweight ad hoc networks.As the load of network increases,QoS(Quality of Service) is degraded obviously.In this paper,we analyze the impact of network load on MAODV protocol,and propose an optimized protocol MAODV-BB(Multicast Ad hoc On-demand Vector with Backup Branches),which improves robustness of the MAODV protocol by combining advantages of the tree structure and the mesh structure.It not only can update shorter tree branches but also construct a multicast tree with backup branches.Mathematical analysis and simulation results both demonstrate that the MAODV-BB protocol improves the network performance over conventional MAODV in heavy load ad hoc networks.     

PPMA, a probabilistic predictive multicast algorithm for ad hoc networks

Ad hoc networks are collections of mobile nodes communicating using wireless media without any fixed infrastructure. Existing multicast protocols fall short in a harsh ad hoc mobile environment, since node mobility causes conventional multicast trees to rapidly become outdated. The amount of bandwidth resource required for building up a multicast tree is less than that required for other delivery structures, since a tree avoids unnecessary duplication of data. However, a tree structure is more subject to disruption due to link/node failure and node mobility than more meshed structures. This paper explores these contrasting issues and proposes PPMA, a Probabilistic Predictive Multicast Algorithm for ad hoc networks, that leverages the tree delivery structure for multicasting, solving its drawbacks in terms of lack of robustness and reliability in highly mobile environments. PPMA overcomes the existing trade-off between the bandwidth efficiency to set up a multicast tree, and the tree robustness to node energy consumption and mobility, by decoupling tree efficiency from mobility robustness. By exploiting the non-deterministic nature of ad hoc networks, the proposed algorithm takes into account the estimated network state evolution in terms of node residual energy, link availability and node mobility forecast, in order to maximize the multicast tree lifetime, and consequently reduce the number of costly tree reconfigurations. The algorithm statistically tracks the relative movements among nodes to capture the dynamics in the ad hoc network. This way, PPMA estimates the node future relative positions in order to calculate a long-lasting multicast tree. To do so, it exploits the most stable links in the network, while minimizing the total network energy consumption. We propose PPMA in both its centralized and distributed version, providing performance evaluation through extensive simulation experiments.     

Adaptive Core Multicast Routing Protocol

The Adaptive Core Multicast Routing Protocol (ACMRP) is proposed for multicast routing in ad hoc networks. ACMRP is on demand core-based multicast routing protocol that is based on a multicast mesh. In ACMRP, a core is not well-known and it adapts to the current network topology and group membership. The enhanced adaptivity minimizes the core dependency and, accordingly, improves performance and robustness of ACMRP. A multicast mesh is created and maintained by the periodic flooding of the adaptive core. Since the flooding traffic is evenly maintained and a mesh provides rich connectivity among group members, ACMRP can achieve efficiency, scalability, and effectiveness. We evaluate scalability and performance of ACMRP via simulation.     

Family ACK tree (FAT): supporting reliable multicast in mobile ad hoc networks

A new protocol, called family ACK tree (FAT), is proposed to support a reliable multicast service for mobile ad hoc networks. For each reliable multicast protocol, a recovery scheme is used to ensure end-to-end delivery of unreliable multicast packets for all group members. FAT employs a tree-based recovery mechanism that localizes ACKs and retransmissions to avoid feedback implosion. To cope with node movements, FAT constructs an ACK tree on which each node maintains reachability information to three generations of nodes on the ACK tree. When a tree is fragmented due to a departed node, the fragments are glued back to the tree using the underlying multicast routing protocol. FAT then adopts an adaptive scheme to recover missed packets that have been multicast to the group during fragmentation and are not repaired by the new reliability agent. We have conducted simulations to compare the performance of FAT with existing solutions. The results show that FAT achieves better performance for the provision of reliable service in ad hoc networks, in terms of reliability, scalability, and delivery efficiency.     

A novel overlay multicast protocol in mobile ad hoc networks: design and evaluation

Despite significant research in mobile ad hoc networks, multicast still remains a research challenge. Recently, overlay multicast protocols for MANET have been proposed to enhance the packet delivery ratio by reducing the number of reconfigurations caused by nongroup members' unexpected migration in tree or mesh structure. However, since data is delivered by using replication at each group member, delivery failure on one group member seriously affects all descendent members' packet delivery ratio. In addition, delivery failure can occur by collision between numbers of unicast packets where group members densely locate. In this paper, we propose a new overlay multicast protocol to enhance packet delivery ratio in two ways. One is to construct a new type of overlay data delivery tree, and the other is to apply a heterogeneous data forwarding scheme depending on the density of group members. While the former aims to minimize influence of delivery failure on one group member, the latter intends to reduce excessive packet collision where group members are densely placed. Our simulation results show distinct scalability improvement of our approach without regard to the number of group members or source nodes.     

Adaptive multicast on mobile ad hoc networks using tree-based meshes with variable density of redundant paths

Multicasting has been extensively studied for mobile ad hoc networks (MANETs) because it is fundamental to many ad hoc network applications requiring close collaboration of multiple nodes in a group. A general approach is to construct an overlay structure such as multicast tree or mesh and to deliver a multicast packet to multiple receivers over the overlay structure. However, it either incurs a lot of overhead (multicast mesh) or performs poorly in terms of delivery ratio (multicast tree). This paper proposes an adaptive multicast scheme, called tree-based mesh with k-hop redundant paths (TBM _k ), which constructs a multicast tree and adds some additional links/nodes to the multicast structure as needed to support redundancy. It is designed to make a prudent tradeoff between the overhead and the delivery efficiency by adaptively controlling the path redundancy depending on network traffic and mobility. In other words, when the network is unstable with high traffic and high mobility, a large k is chosen to provide more robust delivery of multicast packets. On the other hand, when the network traffic and the mobility are low, a small k is chosen to reduce the overhead. It is observed via simulation that TBM _k improves the packet delivery ratio as much as 35% compared to the multicast tree approach. On the other hand, it reduces control overhead by 23–87% depending on the value of k compared to the multicast mesh approach. In general, TBM _k with the small value of k offers more robust delivery mechanism but demands less overhead than multicast trees and multicast meshes, respectively.     

An efficient heterogeneous key management approach for secure multicast communications in ad hoc networks

In a mobile wireless ad hoc network, mobile nodes cooperate to form a network without using any infrastructure such as access points or base stations. Instead, the mobile nodes forward packets for each other, allowing communication among nodes outside wireless transmission range. As the use of wireless networks increases, security in this domain becomes a very real concern. One fundamental aspect of providing confidentiality and authentication is key distribution. While public-key encryption has provided these properties historically, ad hoc networks are resource constrained and benefit from symmetric key encryption. In this paper, we propose a new key management mechanism to support secure group multicast communications in ad hoc networks. The scheme proposes a dynamic construction of hierarchical clusters based on a novel density function adapted to frequent topology changes. The presented mechanism ensures a fast and efficient key management with respect to the sequential 1 to n multicast service.     

Wireless Ad Hoc Multicast Routing with Mobility Prediction

An ad hoc wireless network is an infrastructureless network composed of mobile hosts. The primary concerns in ad hoc networks are bandwidth limitations and unpredictable topology changes. Thus, efficient utilization of routing packets and immediate recovery of route breaks are critical in routing and multicasting protocols. A multicast scheme, On-Demand Multicast Routing Protocol (ODMRP), has been recently proposed for mobile ad hoc networks. ODMRP is a reactive (on-demand) protocol that delivers packets to destination(s) on a mesh topology using scoped flooding of data. We can apply a number of enhancements to improve the performance of ODMRP. In this paper, we propose a mobility prediction scheme to help select stable routes and to perform rerouting in anticipation of topology changes. We also introduce techniques to improve transmission reliability and eliminate route acquisition latency. The impact of our improvements is evaluated via simulation.     

A secure group key management scheme for hierarchical mobile ad hoc networks

In this paper, we present a secure group key management scheme for hierarchical mobile ad hoc networks. Our approach aims to improve both scalability and survivability of group key management for large-scale wireless ad hoc networks. To achieve our goal, we propose the following approaches: (1) a multi-level security model, which follows a modified Bell-La Padula security model that is suitable in a hierarchical mobile ad hoc networking environment, and (2) a decentralized group key management infrastructure to achieve such a multi-level security model. Our approaches reduce the key management overhead and improve resilience to any single point failure problem. In addition, we have developed a roaming protocol that is able to provide secure group communication involving group members from different groups without requiring new keys; an advantage of this protocol is that it is able to provide continuous group communication even when the group manager fails.     

Analysis of tree‐based multicast routing in wireless sensor networks with varying network metrics

Wireless ad hoc and sensor networks are emerging with advances in electronic device technology, wireless communications and mobile computing with flexible and adaptable features. Routing protocols act as an interface between the lower and higher layers of the network protocol stack. Depending on the size of target nodes, routing techniques are classified into unicast, multicast and broadcast protocols. In this article, we give analysis and performance evaluation of tree‐based multicast routing in wireless sensor networks with varying network metrics. Geographic multicast routing (GMR) and its variations are used extensively in sensor networks. Multicast routing protocols considered in the analytical model are GMR, distributed GMR, demand scalable GMR, hierarchical GMR, destination clustering GMR and sink‐initiated GMR. Simulations are given with comparative analysis based on varying network metrics such as multicast group size, number of sink nodes, average multicast latency, number of clusters, packet delivery ratio, energy cost ratio and link failure rate. Analytical results indicate that wireless sensor network multicast routing protocols operate on the node structure (such as hierarchical, clustered, distributed, dense and sparse networks) and application specific parameters. Simulations indicate that hierarchical GMR is used for generic multicast applications and that destination clustering GMR and demand scalable GMR are used for distributed multicast applications. Copyright © 2012 John Wiley & Sons, Ltd.     

Intelligent Internal Stealthy Attack and its Countermeasure for Multicast Routing Protocol in MANET

Multicast communication of mobile ad hoc networks is vulnerable to internal attacks due to its routing structure and high scalability of its participants. Though existing intrusion detection systems (IDSs) act smartly to defend against attack strategies, adversaries also accordingly update their attacking plans intelligently so as to intervene in successful defending schemes. In our work, we present a novel indirect internal stealthy attack on a tree‐based multicast routing protocol. Such an indirect stealthy attack intelligently makes neighbor nodes drop their routing‐layer unicast control packets instead of processing or forwarding them. The adversary targets the collision avoidance mechanism of the Medium Access Control (MAC) protocol to indirectly affect the routing layer process. Simulation results show the success of this attacking strategy over the existing “stealthy attack in wireless ad hoc networks: detection and countermeasure (SADEC)” detection system. We design a cross‐layer automata‐based stealthy attack on multicast routing protocols (SAMRP) attacker detection system to identify and isolate the proposed attacker. NS‐2 simulation and analytical results show the efficient performance, against an indirect internal stealthy attack, of SAMRP over the existing SADEC and BLM attacker detection systems.     

A hexagonal-tree TDMA-based QoS multicasting protocol for wireless mobile ad hoc networks

The mobile multimedia applications have recently generated much interest in wireless ad hoc networks with supporting the quality-of-service (QoS) communications. The QoS metric considered in this work is the reserved bandwidth, i.e., the time slot reservation. We approach this problem by assuming a common channel shared by all hosts under a TDMA (Time Division Multiple Access) channel model. In this paper, we propose a new TDMA-based QoS multicast routing protocol, namely hexagonal-tree QoS multicast protocol, for a wireless mobile ad hoc network. Existing QoS routing solutions have addressed this problem by assuming a stronger multi-antenna model or a less-strong CDMA-over-TDMA channel model. While more practical and less costly, using a TDMA model needs to face the challenge of radio interference problems. The simpler TDMA model offers the power-saving nature. In this paper, we propose a new multicast tree structure, namely a hexagonal-tree, to serve as the QoS multicasting tree, where the MAC sub-layer adopts the TDMA channel model. In this work, both the hidden-terminal and exposed-terminal problems are taken into consideration to possibly exploit the time-slot reuse capability. The hexagonal-based scheme offers a higher success rate for constructing the QoS multicast tree due to the use of the hexagonal-tree. A hexagonal-tree is a tree whose sub-path is a hexagonal-path. A hexagonal-path is a special two-path structure. This greatly improves the success rate by means of multi-path routing. Performance analysis results are discussed to demonstrate the achievement of efficient QoS multicasting.     

On-Demand Multicast Routing Protocol in Multihop Wireless Mobile Networks

An ad hoc network is a dynamically reconfigurable wireless network with no fixed infrastructure or central administration. Each host is mobile and must act as a router. Routing and multicasting protocols in ad hoc networks are faced with the challenge of delivering data to destinations through multihop routes in the presence of node movements and topology changes. This paper presents the On-Demand Multicast Routing Protocol (ODMRP) for wireless mobile ad hoc networks. ODMRP is a mesh-based, rather than a conventional tree-based, multicast scheme and uses a forwarding group concept; only a subset of nodes forwards the multicast packets via scoped flooding. It applies on-demand procedures to dynamically build routes and maintain multicast group membership. ODMRP is well suited for ad hoc wireless networks with mobile hosts where bandwidth is limited, topology changes frequently, and power is constrained. We evaluate ODMRP performance with other multicast protocols proposed for ad hoc networks via extensive and detailed simulation.     

Maximizing multicast lifetime in unreliable wireless ad hoc network

Multicast is an efficient method for transmitting the same packets to a group of destinations. In energy-constrained wireless ad hoc networks where nodes are powered by batteries, one of the challenging issues is how to prolong the multicast lifetime. Most of existing work mainly focuses on multicast lifetime maximization problem in wireless packet loss-free networks. However, this may not be the case in reality. In this paper, we are concerned with the multicast lifetime maximization problem in unreliable wireless ad hoc networks. To solve this problem, we first define the multicast lifetime as the number of packets transmitted along the multicast tree successfully. Then we develop a novel lifetime maximization genetic algorithm to construct the multicast tree consisting of high reliability links subject to the source and destination nodes. Simulation results demonstrate the efficiency and effectiveness of the proposed algorithm.     

Approximate minimum-energy multicasting in wireless ad hoc networks

A wireless ad hoc network consists of mobile nodes that are equipped with energy-limited batteries. As mobile nodes are battery-operated, an important issue in such a network is to minimize the total power consumption for each operation. Multicast is one of fundamental operations in any modern telecommunication network including wireless ad hoc networks. Given a multicast request consisting of a source node and a set of destination nodes, the problem is to build a minimum-energy multicast tree for the request such that the total transmission power consumption in the tree is minimized. Since the problem in a symmetric wireless ad hoc network is NP-complete, we instead devise an approximation algorithm with provable approximation guarantee. The approximation of the solution delivered by the proposed algorithm is within a constant factor of the best-possible approximation achievable unless P = NP.     

Probabilistic reliable multicast in ad hoc networks

When striving for reliability, multicast protocols are most commonly designed as deterministic solutions. Such an approach seems to make the reasoning about reliability guarantees (traditionally, binary, “all-or-nothing”-like) in the face of packet losses and/or node crashes. It is however precisely this determinism that tends to become a limiting factor when aiming at both reliability and scalability, particularly in highly dynamic networks, e.g., ad hoc networks. Gossip-based multicast protocols appear to be a viable path towards providing multicast reliability guarantees. Such protocols embrace the non-deterministic nature of ad hoc networks, providing analytically predictable probabilistic reliability guarantees at a reasonable overhead.

This paper presents the Route Driven Gossip (RDG) protocol, a gossip-based multicast protocol designed precisely to meet a more practical specification of probabilistic reliability in ad hoc networks. Our RDG protocol can be deployed on any basic on-demand routing protocol, achieving a high level of reliability without relying on any inherent multicast primitive. We illustrate our RDG protocol by layering it on top of the “bare” Dynamic Source Routing protocol, and convey our claims of reliability and scalability through both analysis and simulation.     

Improving handoff performance by utilizing ad hoc links in multi-hop cellular systems

Handoff performance is a critical issue for mobile users in wireless cellular networks, such as GSM networks, 3G networks, and next generation networks (NGNs). When ad hoc mode is introduced to cellular networks, multi-hop handoffs become inevitable, which brings in new challenging issues to network designers, such as how to reduce the call dropping rate, how to simplify the multi-hop handoff processes, and how to take more advantage of ad hoc mode for better resource management, and most of these issues have not been well addressed as yet. In this paper, we will address some of the issues and propose a scheme, Ad-hoc-Network–Embedded handoff Assisting Scheme (ANHOA), which utilizes the self-organizing feature of ad hoc networks to facilitate handoffs in cellular networks and provide an auxiliary way for mobile users to handoff across different cells. Moreover, we also propose a scheme enabling each BS to find the feasible minimum reservation for handoff calls based on the knowledge of adjacent cells’ traffic information. Due to the use of multi-hop connections, our scheme can apparently alleviate the reservation requirement and lower the call blocking rate while retaining higher spectrum efficiency. We further provide a framework for information exchange among adjacent cells, which can dynamically balance the load among cells. Through this study, we demonstrate how we can utilize ad hoc mode in cellular systems to significantly improve the handoff performance.     

The design, implementation, and performance evaluation of theon-demand multicast routing protocol in multihop wireless networks

Multicasting has emerged as one of the most focused areas in the field of networking. As the technology and popularity of the Internet grow, applications such as video conferencing that require the multicast feature are becoming more widespread. Another interesting development has been the emergence of dynamically reconfigurable wireless ad hoc networks to interconnect mobile users for applications ranging from disaster recovery to distributed collaborative computing. In this article we describe the on-demand multicast routing protocol for mobile ad hoc networks. ODMRP is a mesh-based, rather than conventional tree-based, multicast scheme and uses a forwarding group concept (only a subset of nodes forwards the multicast packets packets via scoped flooding). It applies on-demand procedures to dynamically build routes and maintain multicast group membership. We also describe our implementation of the protocol in a real laptop testbed     

Independent-Tree Ad hoc MulticAst Routing (ITAMAR)

Multicasting is an efficient means of one to many communication and is typically implemented by creating a multicasting tree. Because of the severe battery power and transmission bandwidth limitations in ad hoc networks, multicast routing can significantly improve the performance of this type of network. However, due to the frequent and hard-to-predict topological changes of ad hoc networks, maintenance of a multicasting tree to ensure its availability could be a difficult task. We borrow from the concept of Alternate Path routing, which has been studied for providing QOS routing, effective congestion control, security, and route failure protection, to propose a scheme in which a set of multicasting trees is continuously maintained. In our scheme, a tree is used until it fails, at which time it is replaced by an alternative tree in the set, so that the time between failure of a tree and resumption of multicast routing is minimal. In this paper, we introduce the basic scheme, termed ITAMAR, which is a framework for efficient multicasting in ad hoc networks. We present a number of heuristics that could be used in ITAMAR to compute a set of alternate trees. The heuristics are then compared in terms of transmission cost, improvement in the average time between multicast failures and the probability of usefulness. Simulations show significant gains over a wide range of network operational conditions. In particular, we show that using alternate trees has the potential of improving mean time between interruption by 100–600% in a 50 node network (for most multicast group sizes) with small increase in the tree cost and the route discovery overhead. We show that by renewing the backup tree set, probability of interruptions can be kept at a minimum at all times and that allowing some overlap among trees in the backup set increases the mean time between interruptions.     

Scalable team multicast in wireless ad hoc networks exploiting coordinated motion

In this paper, we study a new multicast paradigm for large scale mobile ad hoc networks, namely team multicast. In team multicast the multicast group does not consist of individuals, rather, of member teams. For example a team may be a special task force that is part of a search and rescue operation. The message must be broadcast to each member of each team in the multicast group. Team multicast is very common in ad hoc networks set up to accomplish some collective tasks, such as for emergency recovery or battlefield applications. A key problem in several of the above applications is scalability to large membership size as well as network size. Our approach exploits motion affinity (more precisely, team members’ coordinated motion) which is typically present when the set of nodes has a commonality of interests. Each team can be viewed as a logical subnet. Within the team a landmark node is dynamically elected. The addresses of and the paths to the chosen landmarks are propagated into the whole network so that a source of a multicast group can route to the landmark of a subscribed team.Our protocol, Multicast-enabled Landmark Ad Hoc Routing (denoted as M-LANMAR), uses tunneling from multicast sources to each landmark of the subscribed team and restricted flooding within the motion group. Simulation study shows that M-LANMAR provides efficient and reliable multicast compared with the application of a “flat” multicast scheme (e.g., ODMRP) that does not exploit team coordinated motion.This paper contains three contributions: a new model for team multicast, with the definition of team dynamics (join, merge, split); the exploitation of team mobility and of landmarks in order to achieve scalable multicast, and; the implementation and performance evaluation of M-LANMAR, a landmark based team multicast scheme.