Multicast overlay spanning trees in ad hoc networks: Capacity bounds, protocol design and performance evaluation q Georgios Rodolakis a, * , Anis Laouiti b , Philippe Jacquet a , Amina Meraihi Naimi a a INRIA, BP 105 Rocquencourt, 78153 Le Chesnay Cedex, France b GET/INT, 91000 Evry, France Available online 26 January 2008 Abstract We study the benefits of multicast routing in the performance of wireless ad hoc networks. In particular we show that if a node wishes to communicate with n distinct destinations, multicast can reduce the overall network load by a factor Oð ffiffi n p Þ, when used instead of uni- cast. One of the implications of this scaling property consists in a significant increase of the total capacity of the network for data deliv- ery. Hence, we show that the aggregate multicast capacity of wireless ad hoc networks is Oð ffiffi n p Þ larger than the unicast capacity, when the group size n is small compared to the total number of nodes in the network. We discuss how these information theoretic results can be taken into consideration in the operation of a multicast protocol for wireless mesh networks using Multicast Overlay Spanning Trees (MOST). We perform simulations of the MOST protocol to compare with the theoretical results, and we present a fully working imple- mentation for real network environments. Ó 2008 Elsevier B.V. All rights reserved. Keywords: Multicast; Overlay; Capacity; Ad hoc; Wireless 1. Introduction An ad hoc or mesh network can be defined as a set of nodes that communicate using the wireless medium, and does not require any pre-existent infrastructure. The main challenge is to offer connectivity between the participating nodes in a multi-hop manner by sharing the same wireless channel. Wireless mesh networks consist of mesh routers and mesh clients, where mesh routers have minimal mobil- ity and form the core of the network. Mesh routers estab- lish an ad hoc network and maintain the mesh connectivity in order to offer network access to mesh clients. Hence, mesh networks can be seen as a special case of ad hoc net- works which deal with limited router mobility, while ad hoc networks cover more general mobility issues. Several pro- tocols have been proposed to provide unicast communica- tions in such environments. Multicast offers an elegant way to establish group com- munication between users by using the concept of multicast groups, which are defined by their corresponding address. Interested clients can join and leave those groups in order to send and/or receive data from other group members. Moreover, the mechanisms which enable multicast commu- nication ensure that an efficient strategy is used to deliver the data packets to all the members simultaneously. There- fore, multicast communication is adequate for a large class of applications, such as video-conferences, multi-player games, streaming applications etc. The previously described requirements make multicast routing an impor- tant and difficult challenge in the Internet, and even more so in ad hoc networks. In fact, mainly due to the dynamic nature of the routes, multicast protocols developed for wired networks cannot operate in the harsher wireless envi- ronment. This creates a need for protocols which are spe- cially adapted to mesh networks. However, although the 0140-3664/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.comcom.2008.01.019 q Some results of this work were presented in ‘‘Multicast Scaling Properties in Massively Dense Ad Hoc Networks”, SANSO, Fukuoka, 2005, and ‘‘Multicast Overlay Spanning Tree for Ad Hoc Networks”, WWIC, Coimbra, 2007. * Corresponding author. Tel.: +33 1 39 63 58 56. E-mail address: georges.rodolakis@inria.fr (G. Rodolakis). www.elsevier.com/locate/comcom Available online at www.sciencedirect.com Computer Communications 31 (2008) 1400–1412