Basically, there is no difference between WiFi and 802.11. WiFi is a marketing term and indicates that the product has been certified by the Wi-Fi Alliance. Wi-Fi Alliance is a trade association and was created in 2009 by a large number of manufacturers and service providers to promote 802.11 and certify the equip- ment to ensure interoperability among different manufacturers equipment.
There are numerous books and articles on the IEEE 802.11 technologies, and therefore, we will not delve further on explaining 802.11 WLAN. We will simply assume that there are access points and gateways that are readily avail- able that can be easily installed to create a mesh network.
In IEEE 802.11, there are two modes of operation: infrastructure-based and infrastructure-less. In the former, the wireless clients (called stations, STA) are connected to an aggregation and routing node called access point (AP), and in the latter, the wireless clients connect directly to each other depending on their reachability. In the infrastructure mode, the set of wireless clients that attach with an AP are collectively called basic service set (BSS). To enable one BSS to communicate with another BSS, they are connected via a wired distri- bution system (DS), and the extended system is called an extended service set (ESS) (see Fig. 4.2). The ESS may be accomplished through a bridge or backhauling the traffic from each AP to the ISP via a broadband connection.
Several vendors have been offering wireless solution to DS, but these have been proprietary solutions limiting interoperability. In the noninfrastructure mode of operation, also called ad-hoc mode (mobile ad-hoc network— MANET), the basic configuration had no provision of multi-hop. Several mechanisms have been proposed to add routing capabilities in the wireless clients to enable multi-hopping. The two main protocols are oLSR (optimized link state routing) and AoDV (ad-hoc on-demand vector) routing. The route discovery in oLSR is basically proactive, and in AoDV, it is reactive. Both are problematic because in MANET, the nodes are mobile, which means that in oLSR, the routing tables have to continuously exchange between nodes even though the nodes have nothing to send. This puts a heavy load on the scarce radio resources and significantly increased overhead. Because of the likeli- hood of the node mobility, although the route discovery happens when a node has something to send, the path can change quickly due to topology change, requiring that the path maintenance techniques are activated several times during a session, resulting in a large latency. To take advantage of both the proactive and reactive protocols, several hybrid protocols have been proposed; one of them, called Hybrid Wireless Mesh Protocol (HWMP), has been adopted in the IEEE 802.11s amendment, which provides efficient topology formation and routing methods.