QoS-aware MAC protocols for wireless sensor networks: A survey <s> QoS provisioning and service differentiation in traditional networks <s> Abstract Recent technological advances have made it possible to havelarge wireless ad-hoc networks of small devices. The primepurpose of such sensor networks is to disseminate informationabout the environmentthey sense. We observethat informationprovidedmayhavedifferent levelsof importanceandarguethatthe sensor networks should be willing to spend more resourcesin disseminating packets carrying more important information.In this paper, weintroducethe conceptof servicedifferenti-ationasapplicabletosensornetworks,highlightitsfundamentaldifferences with normal data networks and deﬁne the relevantmetrics. Variousmechanismswhichmay provideservicescom-patible with the packet priority levels are proposed. We evalu-ate one of the proposedmethod , Adaptive Forwarding Scheme(AFS) and show that our scheme provides the desired levels ofservice. Keywords SensorNetworks,ServiceDifferentiation, AdaptiveForwardingScheme 1. Introduction Technologicaladvanceshavemade it feasible to havesmall de-vices with computation, communication and sensing capabili-ties [1, 2, 3]. These devices run on batteries and thus their ca-pabilities are limited by the available energy. A sensornetworkconsistingofalargenumberofsuchnodescanbeusefulinkeep-ing track of various activities in a givenregion. However, oper-ations performed in such a sensor network have to be energy-efﬁcient becauseof the energy constraints of its nodes.In a sensor network, sensors would sensesome data, pack-etize it and send the packet to a monitor node along a path con-sisting of multiple wireless hops. Researchers have come upwith schemes to provide the functionality required to performthese operations efﬁciently. For routing the data to the moni-tor node, schemeslike Directed Diffusion [4] and Power-awarerouting [5] have been proposed. Clustering schemes [6, 7, 8]group the nodesinto clusters for network management[7]. Lo-cation dissemination schemes [9, 10] provide the sensors withinformation about their locations. Simple and efﬁcient operat-ing system like tinyOS [3] have been designed for these smallnodes. All these works focus on cutting down on the energyrequirements of a sensor network, while providing the minimalfunctionality for the network to operate.We observe that in sensor networks different data packetsmight have different importance.For example, if a temperaturesensorinaforest,senses60Fonanormalspringday,thevalueis <s> BIB001 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> QoS provisioning and service differentiation in traditional networks <s> Wireless local area networks are gaining popularity at an unprecedented rate, at home, at work, and in public hot spot locations. As these networks become ubiquitous and an integral part of the infrastructure, they will increasingly be used for multimedia applications. There is limited QoS support in WLANs, which will become an impediment in deploying multimedia applications. We present a tutorial on QoS support in IEEE 802.11 WLANs with a focus on the distributed MAC protocol of 802.11. Most QoS support mechanisms proposed for 802.11 use well-known techniques such as priority assignment and fair scheduling, and map QoS metrics into some existing 802.11 MAC parameter, thereby avoiding a redesign of the MAC protocol. We provide a taxonomy of the mechanisms and describe the essential concepts, problems, and advantages of each mechanism. From our study, we conclude that choosing the right set of MAC parameters and the QoS mechanism itself to provide predictable QoS in 802.11 networks is still an open problem. <s> BIB002 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> QoS provisioning and service differentiation in traditional networks <s> Holding the promise of making ubiquitous mobile access to IP-based applications and services a reality, wireless local area networks have been deployed in an unlimited way over the last few years. Due to their robust characteristics, distributed MAC protocols are the most widely used mechanisms to arbitrate access to the wireless channel. However, their ability to achieve high medium usage efficiency while providing services with meaningful performance assurances is being challenged by a wide range of existing and emerging applications that have lately migrated from other telecommunication networks to wireless environments. This article aims to provide a comprehensive study of the limitations and merits of mechanisms that have been proposed toward embedding QoS support to distributed wireless MAC protocols. A hybrid scheme that incorporates signaling and information sharing is proposed, and extensive simulation experiments are run to assess the efficiency of the access schemes in maximizing utilization of the wireless bandwidth while providing QoS support for heterogeneous applications. <s> BIB003
Shortly, QoS is the ability of a network to satisfy the certain requirements of the user or application. There are two main types of QoS provision defined in wired and wireless networks: Hard QoS and Soft QoS. The applications that require hard QoS should be provided deterministic QoS guarantees, such as strict bounds on packet delays, bandwidth or packet losses. In soft QoS approach, again the application has tight QoS requirements but the temporal violations on QoS provisioning can be tolerated to a certain extent BIB003 . Service differentiation is the widely adopted scheme in both wired and wireless networks to provide hard/soft QoS guarantees. There are two service differentiation models proposed for conventional computer networks, Integrated services (IntServ)  and differentiated services (DiffServ)  . Aim of both the differentiation models are to prioritize flows or packets, map their priorities into service qualities and provide required service quality by sharing limited resources among them. IntServ model maintains service on a per-flow basis and can be considered as a reservation-based approach. It specifies a fine grained QoS system and follows the hard QoS approach BIB002 . Flows can be considered as data-centric or host-centric where data-centric consideration can be information generated by motion sensors from a commonly used breach path in border surveillance and host-centric consideration can be the stream of packets between a particular source and destination. However, IntServ model has a number of disadvantages which makes it inappropriate for WSNs. Firstly, it is hard to provide guaranteed service quality due to time varying channel capacity on the wireless medium. Second, maintenance of the per-flow states of the sensor nodes and scalability for dense networks is a real challenge. Third, IntServ model requires a reliable in-band or out-of-band QoS signaling within the sensor network for resource reservation which is very hard to assure in WSNs. DiffServ model maintains service on a per-packet basis and can be considered as a reservation-less approach. Major drawback of DiffServ model is its costly memory requirement since every network entity will behave as a source and an intermediate hop. However, lightweight and easy-to-implement DiffServ model can be adapted to WSNs easily and this model operates in a multi-hop manner BIB001 . Each packet will have a degree of importance and this will be apparent for every entity of the network. In this way, each layer of the communication protocol stack can treat the packet by the way its priority imposes. Therefore, DiffServ model will be assumed as the default service differentiation method for the rest of our work. Fig. 1 shows the concepts of IntServ and DiffServ models discussed in this section.