Wireless mesh networks (WMNs) are dynamically self-organized and self-configured, with the nodes in the network automatically establishing an ad hoc network and maintaining the
mesh connectivity. WMNs are comprised of two types of
nodes: mesh routers and mesh clients. Other than the routing capability for gateway/bridge functions as in a conventional wireless router, a mesh router contains additional routing
functions to support mesh networking. Through multi-hop
communications, the same coverage can be achieved by a
mesh router with much lower transmission power. To further
improve the flexibility of mesh networking, a mesh router is usually equipped with multiple wireless interfaces built on
either the same or different wireless access technologies. In spite of all these differences, mesh and conventional wireless routers are usually built based on a similar hardware platform. Mesh routers have minimal mobility and form the mesh
backbone for mesh clients. Thus, although mesh clients can
also work as a router for mesh networking, the hardware platform and software for them can be much simpler than those
for mesh routers. For example, communication protocols for
mesh clients can be light-weight, gateway or bridge functions do not exist in mesh clients, only a single wireless interface is needed in a mesh client, and so on.
In addition to mesh networking among mesh routers and
mesh clients, the gateway/bridge functionalities in mesh
routers enable the integration of WMNs with various other
networks. Conventional nodes equipped with wireless network
interface cards (NICs) can connect directly to WMNs through
wireless mesh routers. Customers without wireless NICs can
access WMNs by connecting to wireless mesh routers through,
for example, Ethernet. Thus, WMNs will greatly help users to be always-on-line anywhere, anytime.
Consequently, instead of being another type of ad-hoc networking, WMNs diversify the capabilities of ad-hoc networks.
This feature brings many advantages to WMNs, such as low
up-front cost, easy network maintenance, robustness, reliable service coverage, etc. Therefore, in addition to being widely accepted in the traditional application sectors of ad hoc networks, WMNs are undergoing rapid commercialization in
many other application scenarios such as broadband home networking, community networking, building automation, highspeed
metropolitan area networks, and enterprise networking.
To date, several companies have already realized the
potential of this technology and offer wireless mesh networking products. A few testbeds have been established in university research labs. However, for a WMN to be all it can be,
considerable research efforts are still needed. For example, the available MAC and routing protocols are not scalable;
throughput drops significantly as the number of nodes or hops in WMNs increases. Thus, existing protocols need to be
enhanced or re-invented for WMNs. Researchers have started
to revisit the protocol design of existing wireless networks, especially of IEEE 802.11 networks, ad hoc networks, and
wireless sensor networks, from the perspective of wireless
mesh networking. Industrial standards groups, such as IEEE
802.11, IEEE 802.15, and IEEE 802.16, are all actively working on new specifications for WMNs.
In this article we present a survey of recent advances in
protocols and algorithms for WMNs. Our aim is to provide a
better understanding of research challenges of this emerging technology. The rest of this article is organized as follows. The network architectures of WMNs are first presented, with an
objective to highlight the characteristics of WMNs and the
critical factors influencing protocol design. A detailed study on recent advances of WMNs is then carried out, with an
emphasis on open research issues. The article concludes with final remarks.
Network Architecture and
Critical Design Factors