Admission Control Schemes for 802.11-Based Multi-Hop Mobile Ad hoc Networks: A Survey

Mobile ad hoc networks (MANETs) promise unique communication opportunities. The IEEE 802.11 standard has allowed affordable MANETs to be realised. However, providing Quality of Service (QoS) assurances to MANET applications is difficult due to the unreliable wireless channel, the lack of centralised control, contention for channel access and node mobility. One of the most crucial components of a system for providing QoS assurances is admission control (AC). It is the job of the AC mechanism to estimate the state of the network's resources and thereby to decide which application data sessions can be admitted without promising more resources than are available and thus violating previously made guarantees. Unfortunately, due to the aforementioned difficulties, estimating the network resources and maintaining QoS guarantees are non-trivial tasks. Accordingly, a large body of work has been published on AC protocols for addressing these issues. However, as far as it is possible to tell, no wide-ranging survey of these approaches exists at the time of writing. This paper thus aims to provide a comprehensive survey of the salient unicast AC schemes designed for IEEE 802.11-based multi-hop MANETs, which were published in the peer-reviewed open literature during the period 2000-2007. The relevant considerations for the design of such protocols are discussed and several methods of classifying the schemes found in the literature are proposed. A brief outline of the operation, reaction to route failures, as well as the strengths and weaknesses of each protocol is given. This enables patterns in the design and trends in the development of AC protocols to be identified. Finally, directions for possible future work are provided.