Elsevier

Computer Networks

Volume 51, Issue 3, 21 February 2007, Pages 823-834
Computer Networks

A novel adaptive protocol for lightweight efficient multicasting in ad hoc networks

https://doi.org/10.1016/j.comnet.2006.06.008Get rights and content

Abstract

In group communications, we find that current multicast protocols are far from “one size fits all”: they are typically geared towards and optimized for particular scenarios. As a result, when deployed in different scenarios, their performance and overhead often degrades significantly. A common problem is that most of these protocols incur high overheads with a high density of group members and in high mobility. Our objective is to design a protocol that adapts in response to the dynamics of the network. In particular, our objective is to provide efficient and lightweight multicast data dissemination irrespective of the density of group members and node density. Our work is motivated by two observations. First, broadcasting in some cases is more efficient than multicasting. Second, member and node layout distributions are not necessarily homogeneous. For example, many MANET applications result in a topological clustering of group members that move together. Thus, we develop Fireworks, an adaptive approach for group communications in mobile ad hoc networks. Fireworks is a hybrid 2-tier multicast/broadcast protocol that adapts to maintain performance given the dynamics of the network topology and group density. In a nutshell, our protocol creates pockets of broadcast distribution in areas with many members, while it develops a multicast backbone to interconnect these dense pockets. Fireworks offers packet delivery statistics comparable to that of a pure multicast scheme but with significantly lower overheads.

Introduction

Nodes can be distributed and move in clustered patterns in several MANET applications such as disaster recovery missions and military operations. We believe that this formation of the clustered topology could potentially be exploited to reduce the overhead incurred in multicasting. Such clustered topologies are typically characterized by sets of densely packed multicast group members within localized regions. Thus, one could simplify routing by regarding these sets as independent routing entities.

Most of the existing protocols that have been developed thus far [1], [2], [3], [8], [9], [10] do not take the affinity of group members into consideration when constructing their multicast delivery structure. A common problem with these protocols is that the control overhead could be unreasonably large, when the network manifests a dense distribution of group members globally or locally. The control overhead can be high when all the group members are required to participate in the construction and maintenance of the multicast structure. Furthermore, in a mobile environment, a large structure can be frequently under repair.2

This work is motivated by two observations. First, we observe that a simple broadcast scheme can significantly reduce the control overhead in scenarios wherein the density of group members is high [4]. As a rule of thumb, broadcasting seems more efficient when 40% or more of the nodes in the network are group members. Second, many current protocols cannot adapt to local variations in network properties. Most of these protocols have static, globally predefined, parameters that cannot be adjusted dynamically within localized regimes. Our objective then is to design a new protocol that (a) exploits the advantages of broadcasting in high densities and (b) provides localized flexibility in response to changing network conditions.

We propose Fireworks, an adaptive multicast/broadcast protocol that exploits group members affinity to simplify routing and invoke broadcast operations in appropriate localized regimes. Fireworks dynamically identifies and organizes the group members into cohorts which correspond to areas of high group member affinity. In each of these “dense” neighborhoods, one of the group members is selected to be a cohort leader. Cohort leaders have two main functions: (a) they establish a sparse multicast tree among themselves and the source, and (b) they use broadcasting (with adaptive scope) to deliver the packets to other group members in their cohort.

The advantages of this approach are the high adaptability to local properties leading to significantly reduced overheads. This is achieved for the following three reasons: (a) Fireworks reduces the number of group members that participate in the formation and maintenance of the multicast structure and in turn lowers the control overhead, (b) the use of broadcasting in the cohort region maximizes the “wireless broadcast advantage”3 [13], and (c) the local broadcasts are resistant to changes in the local neighborhood due to mobility.

We perform extensive simulations to evaluate the performance of Fireworks. We study a wide range of scenarios by varying the group sizes, the node mobilities, the number of sources, the traffic load, and the spatial distributions of group members in order to understand the limits of the performance of group communications. More specifically, we compare the performance of Fireworks with that of ODMRP [2]. ODMRP has been shown previously to compare favorably with most previously proposed multicast protocols [5]. Fireworks is shown to perform comparably with ODMRP in terms of the packet delivery statistics but with significantly lower overheads. In the presence of multiple group communications sessions or other unicast connections in the network (as the case would be in typical deployment scenarios), this reduction in overheads is especially desirable.

The rest of the paper is organized as follows: in the next section, we provide a detailed description of our proposed protocol. In Section 3, we present our simulation framework and discuss the observed results. Comparisons with ODRMP are also deliberated in this section. We discuss some related works in Section 4 and conclude the paper in Section 5.

Section snippets

Protocol description

Fireworks, as its name implies, forms a fireworks-like4 group communications structure for data packet delivery. Specifically, it constructs a 2-tier hierarchical structure (see Fig. 1) where the upper tier is formed by a

Performance evaluation

In order to evaluate the performance of Fireworks, we implement and simulate the protocol in NS-2 [6] and compare the obtained performance with that of the well-known multicast protocol, the On-Demand Multicast Routing Protocol (ODMRP). We pick ODMRP as a baseline protocol since it has shown to be one of the elite protocols in its class [5].

We divide our evaluations into two parts. In the first part, we evaluate the performance of Fireworks under randomly constructed network scenarios. In these

Related works

Numerous multicast protocols have been developed for use in MANETs. MAODV [1] is a multicast extension of its unicast counterpart. ODMRP [2] is a mesh-based multicast protocol which creates a mesh structure for reliable data delivery. CAMP [8] constructs a group-shared mesh which makes use of a core node to reduce the control traffic needed for receivers to join group. AMRIS [9] makes use of ID number to guide the construction of a tree-based shared multicast structure which supports multiple

Conclusions

In this paper, we propose a new hybrid multicast/broadcast scheme for MANETs. The construction is primarily geared towards reducing overheads incurred with group communications in MANETs. Fireworks exploits the property that the use of a broadcast scheme in an area of densely distributed group members could significantly reduce protocol overhead. It takes the group members affinity into account in constructing the data delivery structure and dynamically partitions a multicast group into several

Lap Kong Law received his B.S. degree in Computer Science from The Chinese University of Hong Kong in 2002. He is currently a Ph.D. candidate in the Department of Computer Science and Engineering, University of California, Riverside. His research interests inculde routing protocols for unicast, broadcast and multicast communications in ad hoc networks, TCP performance over wireless networks and capacity analysis of cellular/ad-hoc hybrid networks.

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Lap Kong Law received his B.S. degree in Computer Science from The Chinese University of Hong Kong in 2002. He is currently a Ph.D. candidate in the Department of Computer Science and Engineering, University of California, Riverside. His research interests inculde routing protocols for unicast, broadcast and multicast communications in ad hoc networks, TCP performance over wireless networks and capacity analysis of cellular/ad-hoc hybrid networks.

Srikanth V. Krishnamurthy received his Ph.D. degree in electrical and computer engineering from the University of California at San Diego in 1997. From 1998 to 2000, he was a Research Staff Scientist at the Information Sciences Laboratory, HRL Laboratories, LLC, Malibu, CA. Currently, he is an Associate Professor of Computer Science at the University of California, Riverside. His research interests span CDMA and TDMA technologies, medium access control protocols for satellite and wireless networks, routing and multicasting in wireless networks, power control, the use of smart antennas and security in wireless networks. He has been a PI or a project lead on projects from various DARPA programs including the Fault Tolerant Networks program, the Next Generation Internet program and the Small Unit Operations program. He is the recipient of the NSF CAREER Award from ANI in 2003. He has also co-edited the book “Ad Hoc Networks: Technologies and Protocols” published by Springer Verlag in 2005. He has served on the program committees of INFOCOM, MOBIHOC and ICC and is the associate editor-in-chief for ACM MC2R.

Michalis Faloutsos is a faculty member at the Computer Science Department in the University of California, Riverside. He got his bachelor’s degree at the National Technical University of Athens and his M.Sc. and Ph.D. at the University of Toronto. His interests include, Internet protocols and measurements, multicasting, cellular and ad-hoc networks. With his two brothers, he co-authored the paper on powerlaws of the Internet topology (SIGCOMM’99), which is in the top 15 most cited papers of 1999. His work has been supported by several NSF and DAPRA grants, including the prestigious NSF CAREER award. He is actively involved in the community as a reviewer and a TPC member in many conferences and journals.

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Prepared through collaborative participation in the Communications and Networks Consortium sponsored by the US Army Research Laboratory under the Collaborative Technology Alliance Program, Cooperative Agreement DAAD19-01-2-0011. The US Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation thereon.

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