Supporting soft real-time services in MANETs using distributed admission control and IEEE 802.11e technology Carlos T. Calafate, Pietro Manzoni, and Manuel P. Malumbres Polytechnic University of Valencia, Valencia, Spain Phone: +34.96.387.7007 - Fax: +34.96.387.7579 E-mail: calafate, pmanzoni, mperez @disca.upv.es Abstract QoS support in MANETs is a hard and challenging task due to the intrinsic complexities of these networks. In this work we present a solution called DACME to support real-time services in MANETs based on distributed admis- sion control. Using the IEEE 802.11e MAC technology as our basis for traffic differentiation, we develop a technique based on probes to assess available bandwidth in an end-to- end path, as well as the end-to-end delay and jitter. Results show that our technique is quite promising due to the de- gree of accuracy achieved estimating the different network parameters, while maintaining acceptable levels of traffic overhead and admission delay. Also, since no demands are imposed on intermediate stations, it can be easily deployed. 1 Introduction In the Internet domain there are two distinct Quality of Service models, which are known as Integrated Ser- vices and Differentiated Services. Mobile Ad hoc Networks (MANETs) differ greatly from the Internet environment, and so the development of a QoS framework for MANETs requires adopting a much more flexible philosophy of coop- eration and resource sharing among users. In MANETs we can devise two main policies for re- source management and user control. The first one follows the Master / Slave paradigm, where one person or entity (Master) has practically all the control over the slave de- vices, both in terms of their components (including hard- ware and software), as well as control over how users will operate them. However, it can only be deployed in very limited situations. The second policy drops the Master / Slave paradigm, embracing cooperation among equals in- stead. This cooperation may be based on the willingness to achieve mutual benefit, or enforced through “punishment” of selfish nodes. Anyway, there is always a notion of strong This work was supported by the Ministerio de Ciencia y Tecnologia under grant TIC/2003/00339, and the Junta de Comunidades de Castilla La-Mancha under grant PBC/03/001. dependency among users and complex interactions in the network, which can be remarkably well described using game theory [1] when nodes behave selfishly. To the best of our knowledge, previous proposals for QoS support in MANETs require that all MANET stations implement some sort of resource reservation or admission control mechanism, fitting perfectly in the first policy for resource management and user control described before. If only a few stations do not implement these mechanisms, then the whole QoS architecture fails or is hindered. Exam- ples of such proposals are FQMM [2], INSIGNIA [3] and SWAN [4]. FQMM [2] has been presented as a flexible QoS model for MANETs. It proposes a hybrid per-flow and per-class QoS provisioning scheme where the IEEE 802.11 MAC layer is used without changes. In a later work [5] authors find that their proposal fails when UDP traffic gets higher priority than TCP. Lee et al. [3] proposed INSIGNIA, an in-band signaling system that supports fast reservation, restoration and adap- tation algorithms. With INSIGNIA all flows require admis- sion control, resource reservation and maintenance at all in- termediate stations between source and destination to pro- vide end-to-end quality of service support. However, Geor- giadis et al. [6] show that bandwidth reservation in multihop wireless networks is an NP-complete problem. Ahn et al. [4] designed SWAN, a stateless net- work model aiming at providing service differentiation in MANETs. SWAN’s admission control mechanism requires all stations to keep track of the MAC’s transmission delay of all packets in order to estimate available bandwidth; such estimation, though, can be deviated because an IEEE 802.11 radio performs adaptive rate control and also because sta- tions may dynamically select different RTS/CTS and frag- mentation thresholds. Such factors difficult the deployment of SWAN in real-life environments. In this work we propose a solution which we named Distributed Admission Control for Manet Environments (DACME). DACME offers a new framework for QoS sup- port in MANETs based on MAC-level QoS support offered by the IEEE 802.11e [7] technology. DACME uses differ- 1