Design and implementation of CLASS: A Cross-Layer ASSociation scheme for wireless mesh networks

This paper focuses on the design and implementation of CLASS, a Cross-Layer Association scheme for IEEE 802.11-based multi-hop wireless mesh networks. The widely-used association strategy in traditional IEEE 802.11 wireless LANs allows a Mobile Station (MS) to scan wireless access links and then associate with the Access Point (AP) that has the best Received Signal Strength Indication (RSSI) value. Unlike traditional wireless LANs, IEEE 802.11-based wireless mesh networks consist of a multi-hop wireless backhaul. As such, the performance experienced by an MS after association with a specific Mesh Access Point (MAP) depends heavily on the conditions of both the access link (e.g., traffic load of associated stations, the frame error rate between an MS and an MAP) and the mesh backhaul (e.g., end-to-end latency and asymmetric uplink/downlink transportation costs). That is, selecting the MAP that yields the “best” performance depends on several factors and cannot be determined solely on the RSSI of the MS-MAP access link. CLASS uses an end-to-end airtime cost metric to determine the MAP to which an MS should associate. The airtime cost metric is based on the IEEE 802.11s, and comprises the access link airtime cost and the backhaul airtime cost. The proposed association scheme considers the frame error rate for various packet sizes, the available bandwidth on the access link after the association of the new MS, and the asymmetric uplink and downlink transportation costs on the backhaul. All experimental results are based on actual Linux-base testbed implementation. We also implement a general Cross-Layer Service Middleware (CLSM) module that is used to monitor network conditions and gather relevant metrics and factor values. Experimental results show that the proposed association scheme is able to identify the MAP which yields the highest end-to-end network performance for the mobile stations after their associations.