IEICE TRANS. FUNDAMENTALS, VOL.E90–A, NO.7 JULY 2007 1333 PAPER Special Section on Multi-dimensional Mobile Information Networks A Tree-Based Channel Assignment and Sibling-Aware Routing Protocol for Multi-Channel Wireless Mesh Networks Bing ZHANG †a) , Member, Mehdad N. SHIRAZI † , and Kiyohiko HATTORI † , Nonmembers SUMMARY Wireless mesh networks (WMNs) are gaining significant momentum as a promising technology for the next-coming state-of-the-art wireless networking. Among many factors, the performance of WMNs would be largely affected by the properness of the deployed routing pro- tocols and the efficient usage of wireless resources. Routing protocols are required to well capture WMNs’ features while wireless channels should be used efficiently in order to accommodate high amount of traffics over the mesh backbone. Recently, a Tree-based Routing (TBR) protocol become a popular state-of-the-art proactive routing protocol and its tree-based broad- casting become an often used technique. Though TBR protocol is well- suited for WMNs’ architecture and the skewed nature of traffic toward the root, the protocol in its current form faces issues which has to be addressed. Specifically, when some or all nodes are equipped with multiple radios, to reduce collision and co-channel interference, not only the parent-child re- lationship but also the sibling relationship need to be constructed by the TBR protocol in the multi-channel WMNs. In this paper, we propose a hybrid tree-based protocol for concurrent routing and channel assignment over WMNs. The protocol makes use of sibling links to mitigate the afore- mentioned shortcomings of TBR protocol. Moreover, in order to address high backbone traffic, the protocol integrates a receiver-based channel as- signment scheme. The protocol efficiently deploys the parent-child topo- logical relationships of nodes to enhance efficiency of broadcast transmis- sions over receiver-based multi-channel WMNs. Simulation results over NS-2 network simulator reveal that our proposed hybrid tree-based proto- col achieves much higher performance than the utilization of the original receiver-based CA and TBR protocol. key words: wireless mesh networks, channel assignment, routing protocol, VoIP 1. Introduction IEEE 802.11 [1] is a widely used wireless communication technology. Although the standard was developed for build- ing single-hop wireless local area networks (WLANs), it has since been used in multi-hop ad-hoc networks as well. WLAN was provisioned as an access technology for con- nection to the Internet where client nodes access to the Internet through wired connected access points. Ad hoc networks, however, were mainly considered for military applications and disaster relief, where mobility and self- organized network configuration is of a primary concern. Recently, 802.11 based Wireless Mesh Networks (WMNs) are becoming popular as a promising technol- ogy for the next-coming state-of-the-art wireless networking [2]–[4]. WMNs deploy ad hoc network technology within Manuscript received November 1, 2006. Manuscript revised January 18, 2007. Final manuscript received March 23, 2007. † The authors are with National Institute of Information and Communications Technology, Kyoto-fu, 619-0289 Japan. a) E-mail: zhang@nict.go.jp DOI: 10.1093/ietfec/e90–a.7.1333 a network architecture which mainly differs with WLAN in that wired backbone is replaced with a wireless mesh of nodes. WMNs consist of mesh access points (MAPs), mesh points (MPs), and mesh clients (MCs). MAPs form the back-bone of the network and forward packets in be- half of other nodes that may not be within direct wireless transmission range of their destinations. MPs can be either stationary or mobile and can form a mesh network between themselves and MAPs. MCs are connected to MAPs and use the wireless mesh backbone for end-to-end communica- tion. Connection to the Internet is made available through wired gateways/portals. WMNs are similar to ad hoc networks in the sense that nodes automatically establish and maintain mesh connectiv- ity among themselves. This feature brings many advantages including low up-front cost, easy network maintenance, ro- bustness, and reliable service coverage. WMNs, however, differ from ad hoc networks in some aspects. Firstly, nodes in WMNs have minimal mobility. Topology changes are therefore in-frequent, and occur only due to occasional node failures, node shut-down for maintenance, or addition of new nodes. Secondly, the traffic distribution in a WMN is typically skewed, as most of the user traffic is directed to/from a wired network [5]. As compared to mobile ad hoc networks, where re- active routing protocols are prevalent, due to the fixed or low mobility of MAPs and MPs, and the need for reduc- ing packet delay, proactive routing protocols are deemed more suitable for WMNs. However, proactive ad hoc rout- ing protocols do not take into account the fact that traffic distribution in WMNs is skewed towards or from a wired network [2], [5]. Tree-based routing protocol well captures these features of WMNs, and is getting increasing attention as a viable routing protocol for WMNS. Tree-based rout- ing protocols were proposed based on a premise that traffics are mostly directed to/from a wired network through a mesh portal. Though, tree-based routing protocols are well suited to such needs, if the network size grows and become signif- icantly large, traffic around the root of the network can be- come very heavy. This can degrade performance and slow down the whole network. This issue can be mitigated by us- ing multiple trees rather than a single one. Nevertheless, the envisioned applications of WMNs warrant the need for in- tra mesh traffics as well. Routing intra mesh traffics through the root node not only aggravate the aforementioned weak point of tree-based routing protocols but also waste efficient usage of network resources due to skewed routing of traffics Copyright c  2007 The Institute of Electronics, Information and Communication Engineers