A study of QoS Aware MAC Protocols for Wireless Multimedia Sensor Networks

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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal, Volume 4, Issue 2, February 2014)

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A study of QoS Aware MAC Protocols for Wireless

Multimedia Sensor Networks

Shubha Rao V

1

, Dr. M. Dakshayini

2

1

VTU & Assistant Professor, 2Professor, Department of Information Science, BMS College of Engineering, Bangalore

Abstract—The availability of inexpensive hardware such as CMOS cameras and microphones has raised the development of Wireless Multimedia Sensor Networks (WMSNs), These networks are collection of wireless interconnected devices that are able to universally access multimedia content such as video and audio streams, still images, and scalar sensor data from the environment. WMSN has gained popularity because of their flexibility in solving problems in different domains. They have potential to change our lives in many different ways. It is employed in wide range of application areas such as target detection and tracking, military and environmental mentoring. These applications are critical to the extent of saving Human life. Hence Reliable service and timely information is very important requirement in WMSN. QoS in WMSN has some techniques and provide such reliable and authenticated information. QoS techniques are employed in each layer of the protocol stack. Emphasis is given to QOS support at the MAC layer. This paper provides a study on QOS aware MAC protocols in Wireless Multimedia Sensor networks and also highlights the main current challenges in designing such protocols.

Keywords— Wireless Multimedia Sensor Networks, Sensor Node,QoS,MAC protocols..

I. INTRODUCTION

Wireless Sensor Networks are defined as a self configured and infrastructure less wireless network to monitor the physical or environmental conditions. It consists of hundreds of thousands of sensor nodes. Sensor nodes are made up of four basic components: sensing unit, processing unit, transceiver unit and power unit. Sensor nodes communicate with each other using radio signals. Each node is inherently resource constrained: They have

limited processing speed, storage capacity and

communication bandwidth. Sensor nodes are deployed either randomly or in a fixed pattern depending upon the application. Once deployed, they are responsible for self-organizing an approximate network infrastructure with multi-hop communication with them to collect information of interest. WSN devices also respond queries sent from a “control-site” to perform specific instructions.

Sensor nodes work either in continuous mode or event driven mode. To know the location of sensor nodes GPS and local positioning algorithms are used [1].

Wireless Sensor networks can sense and process scalar data such as temperature, humidity, pressure etc. of the

physical environment. Further the availability of

inexpensive multimedia devices such CMOS camera and microphones have led to the development of wireless multimedia sensor networks [WMSN]. These multimedia devices can capture multimedia content such as scalar data, stream audio, and video from the environment. WMSN has gained popularity because of their flexibility of solving problems in different domains. They have potential to change our lives in many different ways. It is employed in wide range of application areas such as target detection and tracking, military and environmental mentoring. These applications are critical to the extent of saving Human life. Hence Reliable service and timely information is very important requirement in WMSN [2]. QoS in WMSN has some techniques and provide such reliable and authenticated information. But providing QoS support is a challenging issue due to highly resource constrained nature of sensor network, unreliable wireless links and harsh operation environments. The term QoS is extensively used in all the areas of computer networks. QoS helps to assign different priorities to different users, applications, packets, frames and dataflow based on their requirements by providing restricted resource sharing. Therefore high level of performance can be obtained through a set of measurable parameters such as delay, jitter, available bandwidth and packet loss.

QoS in WMSN implements policies for prioritization of specific application functions.

QoS techniques are employed in each layer of the protocol stack as shown in figure 1.

A brief overview of these techniques are given here

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International Journal of Emerging Technology and Advanced Engineering

739 Figure 1

MAC Layer: Scheduling medium access and the sequence of packets to be sent are changed to meet QoS requirements. This can be achieved by packet reordering and by priority control and admission policies.

Network Layer: It is similar to MAC layer. We can use packet prioritization depending on priority, increasing probability of successful delivery of a packet, the number of copies sent and the number of distinct routes for a given packet is adjusted.

Application Layer: Adaptive compression techniques are employed and frequency in which data are sent is adjusted.

Emphasis is given to QOS support at the MAC layer. All the upper layer components are dependent on MAC layer and hence it is very important to focus on this layer for the overall performance of the network. Centralized MAC schemes of traditional networks cannot be applied to WMSN due to large number of sensor nodes, multi hop nature of networks and scalability issues. In this paper, our aim is to assess on the QOS support at the MAC layer and survey the existing protocols in literature.

The remainder of this paper is organized as follows. Background and QoS outlook is described in Section II. QoS Support at MAC layer is discussed in Section III and in Section IV open research issues are listed and finally in Section V we conclude the paper.

II. BACKGROUND AND QOSOUTLOOK

Quality of Service (QoS) is a very commonly used term which different meanings and outlook [3]. Different communities have different interpretation of this term. It refers to the quality as required by the user/application from the application perspective. While QoS in the network means measure of service quality that the network can offer, while maximizing network utilization. This has led to the development of algorithms, protocols and mechanisms that provide QoS support for various set of applications and various networks. A analogous situation is currently observed in WSNs and WMSNs. WMSN networks have more stringent QoS requirements, like low data delay and maximum reliability as compared with traditional WSNs.

QoS Provisioning in traditional networks:

QoS requirements in traditional networks have emerged from multimedia applications. Different multimedia applications have different QoS requirements. Hence network has to provide better service depending upon the application. There are two types of QoS defined in wired and wireless networks: Hard QoS and Soft QoS. The applications that required hard QoS should provide guaranteed QoS services. In soft QoS temporal violations on QoS provisioning can be tolerated to a certain extent.

The commonly used scheme to provide hard and soft QoS for both wired and wireless networks is service differentiation. There are two services differentiation models proposed for conventional computer networks, Integrated services (IntServ) and differentiated services (DiffServ). Both the models provide QoS by sharing the limited resources among them. The goals of both the models are to prioritize flows or packets, map their priorities into service qualities.

IntServ model follows hard QoS approach, it provides service on per flow basis and it can be referred as a reservation-based approach. This model does not suit WSN and WMSN because of its number of disadvantages. It is very difficult to provide guaranteed service due to wireless medium; it is very challenging to maintain per flow states of the sensor nodes and also to scale up the dense network. It is very complicated in WSN and WMSN to provide a reliable in band or out band QoS signal within the sensor network for resource reservation which is a requirement of IntServ model.

DiffServ model can be considered as a reservation less approach, maintains service on a per packet basis. It requires costly memory requirement because every entity will behave as a source and an intermediate hop. It operates in a multihop manner.

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International Journal of Emerging Technology and Advanced Engineering

740 This model can be easily adapted in WSNs and WMSNs. Since each packet is given importance, each layer of communication stack will treat the packet by the priority given to it [4].

QoS standpoint in WSNs and WMSNs:

Chen et al. has classified QoS in WSN‟s and WMSN‟s into two categories: Application specific and Network Specific. Application Specific focuses on quality of the application itself. It is meant for fulfilling the requirements imposed by application such as lifetime coverage, deployment and quality of sensing, number of active sensors. Network specific provides QoS during delivery of data by communication network. Network resources are utilized efficiently in each layer of communication protocol stack to fulfill the requirement imposed by the carried data such as latency, packet loss, and reliability [5]. Importance is given to network specific QoS in WSNs and WMSN‟s. But QoS requirements for different application differ from each other hence application specific requirements are also important for network specific QoS. Instead of investigating the QoS requirements of every application it is better to focus on data delivery models that are used in different applications. Depending on the application requirements there are three basic models: continuous, query driven and event driven model [6].

Continuous model: This is a basic model for traditional monitoring application based on data collection. In this model sensor nodes transmit the sensed data periodically.

Query driven model: In this model data is requested by the sink in the form of query and upon the receiving the query the sensor node pushes the data collected to the sink. Here two way traffic in considered. Environmental control is an example of this class.

Event driven model: In this model sensor nodes pushes data to the sink if an event of interest occurs. Surveillance and target tracking are examples of this model.

QoS challenges in WSNs and WMSNS:

The following is a combination of the various challenges in WSNs and WMSNs [24]

Severe resource constraints: Energy, bandwidth, memory, buffer size, processing capabilities, achievable data rates, and limited transmission power.

Unbalanced traffic: Traffic is directed mainly in WSN and WMSN from large number of sensor nodes to a small number of sink nodes in a burst manner.

Data redundancy: One of the main characteristic of WSN and WMSN is redundancy which is helpful in achieving reliability/robustness requirement. However, it also results in unnecessary power consumption, waste of bandwidth and data rate.

Network dynamics: Due to node failures, wireless link failures, and node mobility, dynamic nature of the WSN and WMSN topology introduces an extra challenge for QOS support.

Energy balance: Balancing energy load between different nodes to prolong the life of the network.

Power consumption: Due to transmission, multimedia compression, packet processing, and mobility. Scalability: Scaling up or down the network by changing the number of nodes should not affect the performance and the required QoS of the network.

Multiple sinks: Having multiple sinks results in having different network requirements.

Multiple traffic types: Sensor nodes can generate different types of traffic. Hence Applications requiring existence of multiple traffic classes add extra challenging issue to QOS support since requirements of traffic classes differ from each other. This would introduce different QoS requirements such as delay and reliability requirements.

Packet criticality: Different packets have different criticality and priority and should be treated differently. For example, type of video frame (I frame).

Time constraints: Multimedia content have certain time constraints and delivery multimedia content after a certain deadline would be very critical.

III. QOSSUPPORT AT MACLAYER

The design of highly efficient and reliable medium access control (MAC) protocols is perilous in wireless sensor networking. The main aim is to provide sufficient transmission capacity while minimizing energy cost under a reasonable network load condition. The survey of existing MAC protocols reveals that there is no standard single MAC protocol.

MAC in WMSNs is important to coordinate the channel access among contending devices. It is preferable that the MAC layer provides reliable, error-free data transfer with

minimum retransmission while meeting the QoS

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International Journal of Emerging Technology and Advanced Engineering

741 Minimizing medium access delay

Minimizing collisions Maximizing reliability

Minimizing energy consumptions

Minimizing interference and maximizing concurrency Maximize network throughput

Enhance transmission reliability Minimize control overhead. Maximizing adaptive to changes. Guarantee a certain level of QoS [20]

QoS mechanisms in WSNs and WMSNs at MAC layer:

The two main functions of the MAC layer are arbitration of the channel and providing error control and recovery schemes. There are bunch of mechanisms used in the existing mac protocols in literature to achieve these functionalities, to improve the performance of the MAC layer and also satisfy the QoS requirements. Properties of these mechanisms are as follows:

Adaptation and Learning, Error control, power control, data suppression and aggregation, clustering, service differentiation: priority assignments and Differentiation methods [21].

QOS aware MAC protocols for WSNS and WMSN existing in literature has been categorized based on the above mechanisms.

A. Error control

The aim of the error control mechanisms is to reduce energy consumption while providing reliable and fast delivery of the sensory data.

In [8] the authors have proposed a protocol called SIFT. This protocol takes into account the spatial correlation property of WSN‟s. Here N reports will be generated to detect the event. Among N , R reports of the detected event are very important and are transmitted with low latency. The base stations can accurately identify the event and eliminate redundancy using these R reports. Authors propose two methods explicit ACK and Implicit ACK to avoid unnecessary redundancy .These methods utilize the broad cast nature of wireless medium.

In [16] the authors have proposed a protocol using optimal retransmission. This is designed for intra vehicular sensor networks and assumes the sensor nodes have only the transmission capability. Here sensors nodes cannot not get acknowledgement from sink node or detect collision, the optimization problem to find the minimum number of retransmission have been designed by the authors. The protocol is very light weight and simple solution for one-hop sensor networks.

B. Adaptation and learning

Adaptation mechanisms at the MAC layer provide QoS by adapting operation parameters of the sensor nodes to the current network conditions according to their local or collaborative observations such as traffic pattern, network topology, collision probability or channel condition. Hence sensor nodes fine tune their operation parameters such as duty cycle, contention window size, back off exponential or transmission slot scheduling and try to accommodate offered traffic load in a more efficient way.

In [9] the authors have designed a QoS aware MAC protocol for event driven applications called PSIFT and it is based on the SIFT protocol. PSIFT is a Carrier Sense Multiple Access (CSMA) based MAC protocol. The inter frame space (IFS) and contention window size for each traffic class is varied to provide traffic differentiation. This method decreases the traffic load in the network and leads to mostly idle sensor nodes. Since redundancy is removed it may lead to unreliable data transmission.

In [10] authors have proposed protocol to offer QoS for multimedia transmission over WSN‟s and to conserve energy. The protocol assumes three different types of traffic in the network: non real time, best effort and streaming video. The MAC scheme basically monitors the sensor nodes and the medium for any changes taking place and collects the necessary statistics like transmission failures and transmitted traffic type. Depending upon the collected information, it changes the Contention window and duty cycle adaptively. This protocol is highly dynamic in operation and adapts very well to the changing network conditions. It also adds overhead and complexity. Idle listening and warmly sleeping problems may also arise.

In [17] HaunPham, SanjayJ has have presented a new adaptive mobility-aware MAC protocol for sensor networks(MS-MAC).The protocol uses any change in received signal level as an indication of mobility and when necessary, trigger the mobility handling mechanism. This protocol can work very energy efficiently when the network is stationary, where as it can maintain some level of network performance when there are mobile sensors. S-MAC is taken as the starting point and extended to support mobile sensors. This works similar to SMAC when nodes are stationary and for mobile adhoc scenario it switches to work similarly to IEEE 802.11.

C Service differentiation

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International Journal of Emerging Technology and Advanced Engineering

742 It differentiates and prioritizes the traffic carried on the network based on one or more criteria and forms several traffic classes. MAC layer treats each of these traffic classes in a different way by managing the resource sharing among them and tries to fulfill the requirements imposed by their degree of importance. It consists of two phases: priority assignment and differentiation between priority levels.

In [11] A. Firoze, L. Ju, L. Kwong assigns different priorities to different type of events monitored by sensor nodes. Service differentiations among these events are provided by varying both contention window size and inter frame space. They do not use RTS-CTS exchange but rather transmits a short pulse to reserve the medium. This reduces the control overhead. To provide acknowledgement powerful broadcast signals are sent from sink to every node in the network. Acknowledgement by intermediate node is not implemented.

In[12] Elhanany proposes a protocol which utilizes intra-node scheduling to select the next serviced packet from five different priority queues and inter-node scheduling to coordinate the medium access among multiple neighboring nodes. Intra node scheduling is achieved using MAX-MIN fairness algorithm for controlling the rate. Packetized generalized processor sharing algorithm is used to select the next transmitted packet. To achieve inter-node scheduling, loosely prioritized random access is proposed for coordinating the medium access. It is based on the transmission urgencies of the nodes which have packets to send. This protocol provides robustness against changing conditions of the sensor network. The calculation of transmission priority of a node is very complex.

In [16] the authors have proposed a new protocol I-MAC which uses hybrid TDMA/CSMA for medium access and introduces a prioritization mechanism access for Z-MAC. The probability of collisions and energy consumption are reduced by using contention based medium access for short periodic control messages and by scheduled medium access for long data packet.

In [16] authors have designed a protocol which uses both features of both contention based and scheduled based approaches and uses a hybrid scheme for medium sharing. There are two phases in this protocol setup phase and transmission phase. In the setup phase global clock synchronization, neighbor discovery and accordingly slot assignment are done. The real data delivery takes place during transmission phase. In heavy traffic conditions the protocol behaves like a TDMA based protocol.

In [19] Yang Liu, itamarelhany, Hairong Qi have developed an innovative Mac protocol (q-MAC). This protocol provides QOS by differentiating network services based on priority levels. The priority levels reflect application priority and state of system resources, residual energy and queue occupancies. The protocol uses both intranode and internodes negotiation. The intranode packet scheduling is multiple queuing architecture with packet classification and weighted arbitration. The protocol also incorporates a power aware scheduling mechanism and loosely priotized random access algorithm which achieves internodes scheduling. The protocol provides flexible differentiation between service classes.

D. Adaptation and learning and Service differentiations

In [13] Elhanany formulates a MAC protocol for packetized wireless sensor networks in terms of an optimization problem related to throughput and overall delay. RL-MAC is a QoS aware reinforcement learning (RL) based protocol and used CSMA scheme. The protocol achieves high through put and low power consumption for a wide range of traffic conditions. The duty cycle of the sensor nodes are changed based on local observation as well as observation of neighboring nodes. The protocol manages network conditions very well.

E. Adaptation and learning and power control

The main idea of power control is simply adjusting the transmission power of the sensor nodes according to the minimum power required for successful transmission.

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International Journal of Emerging Technology and Advanced Engineering

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F. Clustering

Clustering mechanism simplifies the synchronization and coordination by grouping set of neighboring sensor nodes. It provides significant energy saving by improving internodes connectivity and facilitating data aggregation. It can be used to provide QoS support in terms of energy consumption and reliability.

In [21] the authors have proposed a clustered based on demand multichannel MAC protocol (COM-MAQ) to support energy–efficient, high-throughput and reliable data transmissions in WMSNS. The proposed protocol consists of three sessions: request sessions, scheduling sessions and data transmission session. To achieve high energy efficiency, i) a scheduled multichannel access is used within each cluster so that cluster member can operate in a contention-free manner, to avoid collision, idle listening and overhearing. ii) To maximize the network throughput, a traffic adaptive and QoS aware scheduling algorithm is executed to dynamically allocate time slots and channels for sensor nodes based on the current traffic information and QoS requirements. iii) To enhance transmission reliability, a spectrum-aware ARQ is incorporated to better exploit the unused spectrum for a balance between the reliability and retransmissions.

G. Data Suppression and Aggregations:

Data suppression and aggregation mechanisms try to minimize radio communication by reducing the traffic load of the network, hence provides energy savings.

The redundancy can be eliminated by either suppressing the set of messages belonging to the data coming from

different sources. This elimination also prevents

congestions caused by overloading, decreases probability of collision and improves the utilization of the network resources such as bandwidth. Data suppression and aggregation techniques are application specific and similar to error control.

In [22] Data aggregation has been one of the important key techniques to increase energy efficiency and bandwidth utilization in wireless sensor networks. In this paper, authors propose a novel and simple data aggregation protocol, referred to as Lump, which enables to support QoS requirements of applications. For this purpose, it prioritizes packets for differentiated services and facilitates aggregation decision. Its architecture has a cross-layered design that mitigates overheads of in-network processing, and it is completely an independent module residing on between data-link layer and network layer so that it can be applicable to a variety of applications.

IV. RESEARCH ISSUES

Scheduling, admission control and buffer management is an open research issue that has attracted the research community. The other open research areas are i) Simpler QoS models. ii) QoS aware data dissemination protocols. iii) Services. iv) QoS support based on collective QoS parameters [23].

V. CONCLUSION

In this paper, we have presented a study on QoS aware MAC protocols. According to the study we observe that majority of protocols follow a service differentiation approach by classifying the data packets according to their type. Open research issues are also investigated to point out the further investigations in the field of QoS provisioning in WMSN at MAC layer to contribute to future research in the field on WMSNs.

REFERENCES

[1] Mohammad A. Matin “Wireless Sensor Networks - Technology and Protocols”, ISBN 978-953-51-0735-4, 308 pages, Publisher: In Tech, Chapters published September 06, 2012 Under CC BY 3.0 license ,DOI: 10.5772/260

[2] Ian f. Akyildiz, tommasomelodia, kaushik r. chowdhury “A survey on wireless multimedia sensor networks” broadband and wireless networking laboratory, school of electrical and computer engineering, Georgia institute of technology, Atlanta, ga 30332, united states received 11 march 2006; received in revised form 6 august 2006; accepted 5 October 2006

[3] A. Ganz, Z. Ganz, and K. Wongthavarawat, Multimedia Wireless Networks: Technologies, Standards, and QoS, Prentice Hall, Upper Saddle River, NJ, 2004.

[4] S. Bhatnagar, B. Deb, B. Nath, Service differentiation in sensor networks, in: Proceedings of Wireless Personal Multimedia Communications, 2001.

[5] D. Chen, P.K. Varshney, QoS support in wireless sensor networks: a survey, in: Proceedings of the 2004 International Conference on Wireless Networks (ICWN 2004), Las Vegas, Nevada, USA, 2004, pp. 227–233.

[6] S. Tilak, N.B. Abu-Ghazaleh, W. Heinzelman, “A taxonomy of wireless micro-sensor network models”, SIGMOBILE Mobile Computing and Communications Review 6 (2) (2002) 28–36.

[7] Lagkas, Thomas D., et al. "Analysis of queue load effect on channel

access prioritization in Wireless Sensor Networks." Distributed Computing in Sensor Systems Workshops (DCOSSW), 2010 6th IEEE International Conference on. IEEE, 2010.

[8] Jamieson, H. Balakrishnan, Y. Tay, SIFT:”A MAC protocol for event driven wireless sensor networks”, in: Third European Workshop on Wireless Sensor Networks (EWSN 2006), vol. 3868, Zurich,Switzerland, 2006, pp. 260–275.

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744 [10] N. Saxena, A. Roy, J. Shin, “Dynamic duty cycle and adaptive

contention window based QoS-MAC protocol for wireless multimedia sensor networks”, Computer Networks 52 (13) (2008) 2532–2542, doi:10.1016/j.comnet.2008.05.009

[11] A. Firoze, L. Ju, L. Kwong, PR-MAC a priority reservation MAC protocol for wireless sensor networks, in: Proceedings of ICEE ‟07: International Conference on Electrical Engineering, 2007, pp. 1– 6.doi:10.1109/ICEE.2007.4287318.

[12] Y. Liu, I. Elhanany, H. Qi, “An energy-efficient QoS-aware media access control protocol for wireless sensor networks”, in: IEEE International Conference on Mobile Adhoc and Sensor Systems Conference, 2005. doi:10.1109/MAHSS.2005.1542798

[13] Z. Liu, I. Elhanany, RL-MAC: A QoS-aware reinforcement learning based MAC protocol for wireless sensor networks, in: Proceedings of the 2006 IEEE International Conference on Networking, Sensing and Control, ICNSC‟06, 2006, pp. 768–773. Doi: 10.1109/ ICNSC.2006.1673243.

[14] H. Kim, S.-G. Min, “Priority-based QoS MAC protocol for wireless sensor networks”, in: IPDPS ‟09: Proceedings of the 2009 IEEE International Symposium on Parallel& Distributed Processing, IEEE Computer Society, Washington, DC, USA, 2009,pp.1–8. <http://dx.doi.org/10.1109/IPDPS.2009.5161184>.

[15] S. Yoon, C. Qiao, R.S. Sudhaakar, J. Li, T. Talty, “QoMOR: A QoS-aware MAC protocol using optimal retransmission for wireless intravehicular sensor networks”, in: Mobile Networking for Vehicular Environments, 2007, pp. 121–126. doi:10.1109/ MOVE.2007.4300816

[16] I. Slama, B. Shrestha, B. Jouaber, D. Zeghlache, “A hybrid MAC with prioritization for wireless sensor networks”, in: 33rd IEEE Conference on Local Computer Networks, LCN 2008, 2008, pp. 274–281. doi:10.1109/LCN.2008.4664180.

[17] H. Pham, S. Jha,” An adaptive mobility-aware MAC protocol for sensor networks (MS-MAC)”, in: IEEE International Conference on Mobile Ad-hoc and Sensor Systems, 2004, pp. 558–560. doi:10.1109/MAHSS.2004.1392207.

[18] Liu, Zhenzhen, and Itamar Elhanany. "RL-MAC: a QoS-aware

reinforcement learning based MAC protocol for wireless sensor networks." Networking, Sensing and Control, 2006. ICNSC'06. Proceedings of the 2006 IEEE International Conference on. IEEE, 2006.

[19] Yang Liu,Itamarelhanamy,hairong Qi “An energy efficient QOS-aware media access control protocol for wireless sensor networks”:2005 in Proceedings of the IEEE International Conference on Mobile Ad hoc and Sensor Systems

[20] M. AykutYigitel , OzlemDurmazIncel, CemErsoy “QoS-aware MAC protocols for wireless sensor networks: A survey” Computer Networks Research Laboratory, Net lab, Department of Computer Engineering, Bogazici University, Bebek, 34342 Istanbul, Turkey. [21] Li, C., Wang, P., Chen, H. H., & Guizani, M. (2008, May). „A

cluster based on-demand multi-channel MAC protocol for wireless multimedia sensor networks.” In Communications, 2008. ICC'08. IEEE International Conference on (pp. 2371-2376). IEEE.

[22] Jeong, Jongsoo, et al. "A QoS-aware data aggregation in wireless sensor networks." Advanced Communication Technology (ICACT), 2010 The 12th International Conference on. Vol. 1. IEEE, 2010. [23] Islam T Almankawi, MAnel Guerrero Zapata, Jamal N AI-karaki