## 2 Background
### IEEE 802.11s-Based Wireless Mesh Network  
A Wireless Local Area Network (WLAN) is commonly used to provide network access to wireless device users. The most common WLAN uses access points (AP) to provide Internet connectivity to users (STAs). Each AP is connected to a wired LAN. Figure 1 shows the common way to deploy a WLAN. The coverage is limited by the range of the AP. STAs outside the coverage range cannot connect to the AP.  
There are times when wireless repeaters are used to extend the reach of the wireless connection. Wireless repeaters are able to relay wireless frames between an AP and an STA. Wireless repeaters do not require a wired connection, but they must be connected wirelessly to an AP at all times to function. The advantage of using wireless repeaters is that a wired connection is not required. The use of wireless repeaters enables the cost of extending the wireless connection to be relatively lower, and they can be set up in areas where a wired connection cannot reach. However, the wireless connection between the AP and wireless repeater must be set statically during the set-up time. Figure 2 shows how the wireless repeater can extend the coverage of an AP to provide connection to STAs that are farther away. In the figure, the wireless repeater is denoted as Re.  
Figure 1: A basic wireless local area network (WLAN).  
The WMN enables STAs to provide the same functionality as an AP and repeaters. IEEE 802.11s draft defined STAs that support the mesh functionality as mesh station (mesh STA). The STAs shall be able to forward wireless frames and act as APs to connect legacy IEEE 802.11 STAs. A mesh STA that connects the WMN to the Ethernet is defined as a mesh gateway. Figure 3 shows how the wireless network works when IEEE 802.11s is implemented. The coverage will be further extended whenever a mesh STA joins the WMN.  
Figure 4 shows a WMN with additional mesh STAs. The largest difference between a repeater and a mesh STA is the latter's ability to form a wireless connection automatically and efficiently. The best path can be found by using HWMP, which is based on the shortest path algorithm. With HWMP, wireless traffic can be routed in an efficient way through path formation. ALM is used to calculate the link qualities, which are also known as the path distances. If any mesh STA is down, a new path can be formed automatically and efficiently based on HWMP.  
Figure 3: WLAN with a mesh STA.  
Figure 2: WLAN extended with a wireless repeater.  
This WMN deployment guarantees the coverage of the WLAN. However, note that the wireless connection is much slower compared to the wired connection. Thus, this WMN provides the same or larger coverage, but the connections will be slower compared to the conventional approach of using wired APs. Furthermore, multi-hop actions will cause the connection speed to be further decreased. One of the primary considerations when deploying a WMN is to make sure that all mesh STAs can reach the mesh gateway at all times with a sufficient bandwidth. The mesh gateway is also known as a gateway in WSN. In IEEE 802.11s, the mesh STA and the gateway are called a mesh point (MP) and a mesh portal (MPP), respectively.