TY - JOUR AU - Cuneyt, Bayilmis, AB - Abstract Wireless Multimedia Sensor Networks (WMSNs) transmit heterogeneous data having different quality of service and urgency constraints. WMSNs focus on offering QoS for multimedia transmission while Wireless Sensor Networks focus on minimizing energy consumption. To overcome urgency challenges, a new traffic and QoS-aware cross-layer MAC protocol for WMSNs namely urgMAC is proposed in this paper. The urgMAC aims to provide continuous QoS support with video quality tradeoff at the application layer dynamically for applications such as habitat monitoring, military border surveillance and border monitoring containing specific urgency challenges. To this end, the urgMAC includes new mechanisms called Two Tiered Service Differentiation Mechanism, Adaptive Data Rate Adjustment Mechanism, Urgency-based Contention Window Size Adaptation, Traffic Type Adaptive Duty Cycle and Multimedia Message Passing. The urgMAC has been modeled and simulated by Riverbed Modeling and Simulation Software. In addition, the urgMAC is compared with the recent protocols in the literature, and it achieves better results in terms of end-to-end delay and channel utilization. 1. INTRODUCTION Wireless Multimedia Sensor Networks (WMSNs), unlike Wireless Sensor Networks (WSNs), transmit heterogeneous and quality of service (QoS) constrained traffic, such as multimedia and scalar sensory data. The main challenge in WSNs is enhancing lifetime of the network. Research in traditional WSNs is mainly focused on minimizing energy consumption [1]. However, mission-critical and real-time multimedia applications of WMSNs bring forward QoS as a requirement. QoS supported delivery of multimedia traffic in WMSNs is a challenging task. The performance parameters of all layers in protocol stack affect the QoS support. To provide QoS support, the MAC layer appears appropriate, since it affects total performance of the network by organizing medium sharing [2]. MAC schemes are divided into three groups as contentionless, contention-based and hybrid schemes [3]. Contention-based MAC schemes are considered to be more applicable to infrastructureless sensor networks with its easy to implement structure. In addition, contention-based MAC schemes do not need any other information about the network and provide high scalability [4]. QoS supported delivery of multimedia traffic in WMSNs is a challenging task. Several contention-based MAC protocol solutions have been proposed in the literature to provide QoS support; however, the performance parameters at every layer of the protocol stack should be adjusted for QoS provisioning. Research on interaction of different layers called cross-layer mechanisms are receiving an outstanding attention to provide better QoS support [5]. This paper introduces a new traffic and QoS-aware cross-layer WMSN MAC protocol namely urgMAC to provide QoS support for applications that contain specific urgency challenges, such as habitat monitoring, military border surveillance and border monitoring [6]. The urgMAC includes mechanisms called Two Tiered Service Differentiation Mechanism (TSM), Adaptive Data Rate Adjustment Mechanism (ADM), Urgency-based Contention Window Size Adaptation (UCA), Traffic Type Adaptive Duty Cycle (TDC) and Multimedia Message Passing (MMP) to achieve its aim. Although some of these approaches such as TDC and MMP have been applied to the previous WMSN MAC protocols [7–10], the urgMAC applies these mechanisms and its newly proposed mechanisms TSM, ADM and UCA for urgency challenges. The TSM decreases end-to-end delay of the urgent real-time multimedia traffic [11]. Application layer of the protocol stack causes most of the multimedia traffic challenges [12]. The urgMAC utilizes ADM in application layer to reduce congestion or queue overflows in MAC layer [13]. It exploits a carrier sense multiple access/collision avoidance (CSMA/CA) approach. Applying a collision resolution scheme is vital in terms of energy consumption for the CSMA/CA approaches. The UCA adjusts the contention window (CW) size adaptively according to the dynamic network traffic conditions for providing more medium access chance to the nodes with urgent traffic as well as reducing energy consumption. The TDC adjusts active time of the node according to the dominant traffic type for avoiding unnecessary energy consumption. MMP divides larger multimedia packets into the smaller chunks and sends them as a burst to decrease the effect of packet losses. The urgMAC is suitable for military applications such as target tracking, target detection, battlefield monitoring and border surveillance. The urgMAC has been modeled and simulated by Riverbed Modeling and Simulation Software (OPNET) which is based on the discrete event simulation technique. The rest of the paper is organized as follows. Section 2 presents an overview of the contention-based QoS MAC Protocols for WMSNs in the literature. Section 3 addresses the details of the urgMAC. In Section 4, performance analysis of an example networking environment using the urgMAC is clarified, and the conclusion is presented in the final section. 2. CONTENTION-BASED QoS MAC PROTOCOLS FOR WMSNs In order to transmit heterogeneous traffic containing diverse priority constraints, service differentiation for QoS support becomes unavoidable [14]. QoS-aware WMSN MAC protocols employ service differentiation approach because of its easy to implement structure. This approach [15] applies prioritization according to the traffic classes instead of traffic sources. Channel access method of the IEEE 802.11e standard [16] defines four priority classes such as video, voice, background and best effort. The urgMAC offers a service differentiation and prioritization mechanism with a similar approach. The urgMAC’s traffic classes are real-time (RT), non-real-time (NRT) and best effort (BE). Sensor-MAC (SMAC) is a prominent contention-based MAC protocol in the literature. It offers constant sleep–listen periods to increase network lifetime [7]. It does not take into account QoS support; however, its message passing approach is suitable for WMSNs for long multimedia messages to decrease the packet loss rate. The urgMAC exploits the same approach for long multimedia messages. Saxena et al.’s MAC protocol [8] aims to decrease end-to-end delay results of the traffic classes RT, NRT and BE, employing a dynamic duty cycle and an adaptive CW scheme. It has a stop-for-a-round fashion to adjust CW size, whereas the urgMAC adjusts the CW size continuously with its UCA mechanism. The urgMAC also categorizes the traffic into RT, NRT and BE classes similar to [8], but UCA mechanism provides CW size adaptation considering urgency situations. Saxena et al.’s adaptive CW scheme is also utilized in Diff-MAC [9]. Diff-MAC aims to provide fair delivery in a traffic class, based on the hop count metric of each packet. CW size adaptation scheme of urgMAC is similar to the same scheme; however, its UCA mechanism considers urgency situations, whereas Diff-MAC takes into consideration only the traffic classes. Neither Saxena’s MAC protocol nor Diff-MAC offers cross-layer functionality, but the urgMAC provides application layer and MAC layer interaction with its TSM and ADM mechanisms [13] for QoS support. Diff-MAC’s traversed number of hops based prioritization scheme decreases latency for the traffic classes but restricts its usage for an urgency scenario. Cross-layer mechanisms are promising to provide greater QoS support than independent MAC protocols. XL-WMSN is a cross-layer framework that provides a delay and traffic-aware routing, an energy-aware admission control and an end-to-end deadline aware duty cycle mechanism [10]. It employs network and MAC layers to construct a unified cross-layer model. It does not provide application layer interaction to adjust data rate according to the network conditions. Its energy-aware admission control mechanism restricts its usage for an urgency scenario. XL-WMSN does not provide any CW size adaptation scheme to prioritize the traffic classes. Application layer can adjust data rate in a queue overflow or congestion situation to assist MAC layer [17]. In this work [18], a cross-layer scheme is offered with application, network, link and physical layer interactions. It is not a complete MAC protocol. It employs application layer interaction to adjust video quality according to the network conditions. Its adaptive priority queue component does not utilize a fair queuing model; thus, it might cause non-prioritized queues to starve. The urgMAC also employs application layer interaction to construct a cross-layer WMSN MAC protocol. The Diff-MAC and Saxena et al.’s MAC protocol both adjust active time of the sensor node according to the dominant traffic type for avoiding unnecessary energy consumption. The urgMAC also employs the same mechanism with its TDC. The urgMAC differentiate from the protocols in the literature with its cross-layer architecture employing application layer, UCA mechanism with its new urgent traffic-first approach, TDC for avoiding unnecessary energy consumption, MMP to decrease the effect of packet losses and new mechanisms called TSM and ADM. 3. DESIGN OF THE urgMAC In this section, the urgMAC and its key features are introduced. It has a CSMA/CA based medium access scheme with Request to Send/Clear to Send (RTS/CTS) and Acknowledgment (ACK) mechanisms. The structure of the urgMAC is shown in Fig. 1 as a block diagram. Figure 1. View largeDownload slide The block diagram of urgMAC. Figure 1. View largeDownload slide The block diagram of urgMAC. The urgMAC organizes sharing of the medium by employing several mechanisms. These mechanisms are detailed in this section. 3.1. Two tiered service differentiation mechanism (TSM) Contention-based MAC protocols employ traffic classification. The traffic class containing multimedia data has the highest priority to provide QoS support. However, it is vitally important to prioritize the traffic with urgency that needs QoS provisioning, instead of all video sources. The TSM divides traffic into two classes as Urgent Traffic (UT) and Non-urgent Traffic (NUT), and applies service differentiation to both classes. The Weighted Fair Queuing Algorithm (WFQ) is preferred in both level schedulers. The NUT has subclasses such as BE, NRT and RT. The UT has subclasses such as Urgent Best Effort (UBE), Urgent Non-real Time (UNT) and Urgent Real Time (URT). TSM provides QoS support to the URT and prioritize all subclasses of the UT. 3.2. Adaptive data rate adjustment mechanism (ADM) Although proposed TSM provides priority to traffic classes in MAC layer, it does not affect the data rate in the application layer. Therefore, there is a need for a congestion prevention mechanism that interferes with the data rate in a heavy traffic situation. Nowadays, it is possible to adjust the frames per second (fps) rate and the resolution of the multimedia data generated by the sensor cameras. The fps and resolution parameters can be adjusted to maintain QoS support by transmitting a ratio for the number of packets in the multimedia traffic queue to the application layer. TSM performs several steps, at every time interval. It monitors the URT queue and gets the number of packets Pc. It calculates the queue rate Qr as follows. Qs is the packet capacity of the URT queue: Qr=PcQs (1) TSM sends Qr value to application layer and ADM adjusts data rate adaptively by using this value. The flow diagram of TSM and ADM providing cross-layer interaction is presented in Fig. 2. Figure 2. View largeDownload slide Flow diagram of TSM and ADM. Figure 2. View largeDownload slide Flow diagram of TSM and ADM. 3.3. Urgency-based contention window size adaptation (UCA) In the contention-based medium access schemes, the node’s energy source is mostly consumed during send-receive period, contention period and collision resolution. Collisions and retransmissions affect QoS metrics such as throughput, latency and energy efficiency. The urgMAC reduces the number of collisions and allocates the medium by adjusting the CW size adaptively according to the dynamic network traffic conditions and keeps the CW smaller to decrease unnecessary idle listening time. The CW is defined as non-overlapping windows for the UT class and subclasses of the NUT. Varying CW sizes according to traffic types are presented in Fig. 3. The CW size varies according to the increment and decrement coefficients determined between the minimum and maximum values. Figure 3. View largeDownload slide CWs according to traffic types. Figure 3. View largeDownload slide CWs according to traffic types. Algorithm 1. CW size adaptation algorithm 1: CWcur=CWmin 2: EveryδsecondmonitorNt 3: if(Nt)<ϕ gotostep2 4: ComputePfas 5: Pf=NfNf+Ns 6: ifPfγdown(NUT). CW size CWcur starts from the minimum value of the traffic class CWmin. The urgMAC monitors the transmission attempts Nt at every time interval δ. If the number of attempts are higher than a threshold ϕ, it calculates the probability of failure Pf by NfNf+Ns. Nf is the number of failures and Ns is the number of successfully sent packets. If probability of failure is lower than the previous one, decreases the CW size and increases otherwise. 3.4. Traffic type adaptive duty cycle (TDC) The sensor nodes have working modes as transmission, reception, idle listening and sleep. The energy consumption in the idle listening mode is about the same as the consumption in the reception mode, while the consumption in the sleeping mode is much lower. TDC adjusts the node’s active time according to the dominant traffic class and avoids unnecessary energy consumption during idle listening. While nodes with RT are less likely to sleep and transmit QoS-required packets faster, nodes with NRT and BE become less active; thus the packets of RT are prioritized. 3.5. Multimedia message passing (MMP) Unlike wired networks, wireless networks are more prone to communication errors. WMSN nodes produce large data packages of image, video or audio. Large data packets tend to be more error-prone than small packets. Large data packages are divided into smaller chunks; these chunks are sent as a burst without contenting until the whole burst is sent by the MMP mechanism. Thus, the effect of re-sending in packet losses is relatively low. 4. SIMULATION AND PERFORMANCE EVALUATION The performance of the urgMAC was evaluated by using Riverbed Modeling and Simulation Software (OPNET). An example network environment is setup to perform performance evaluation of the urgMAC including TSM, ADM, UCA, TDC and MMP mechanisms. Whereas the total performance of a sensor network depends on the application scenario used, a WMSN scenario with urgency situations has been chosen. A wide range of application scenarios could be considered, for the urgMAC, a critical environment monitoring and urgency situation response scenario was taken into account. In this scenario, the main goal is to ensure rapid transmission of urgent multimedia traffic class. When an urgency situation occurs, all subclasses of UT are prioritized according to other traffic classes. The urgency decision can be made by the monitoring software or by the nodes themselves according to the sensed data on the application layer. The mission of the urgMAC starts after the urgency is detected. Different traffic classes and values determined for the simulation environment are shown in Table 1 and the simulation parameters are shown in Table 2. Table 1. The traffic classes. RT NRT BE Frame rate (fps) Interarrival time (s) Interarrival time (s) Interarrival time (s) Type 1 2 0.500 12 12 Type 2 4 0.250 10 10 Type 3 6 0.166 8 8 Type 4 8 0.125 6 6 Type 5 10 0.100 4 4 Type 6 12 0.083 2 2 RT NRT BE Frame rate (fps) Interarrival time (s) Interarrival time (s) Interarrival time (s) Type 1 2 0.500 12 12 Type 2 4 0.250 10 10 Type 3 6 0.166 8 8 Type 4 8 0.125 6 6 Type 5 10 0.100 4 4 Type 6 12 0.083 2 2 View Large Table 1. The traffic classes. RT NRT BE Frame rate (fps) Interarrival time (s) Interarrival time (s) Interarrival time (s) Type 1 2 0.500 12 12 Type 2 4 0.250 10 10 Type 3 6 0.166 8 8 Type 4 8 0.125 6 6 Type 5 10 0.100 4 4 Type 6 12 0.083 2 2 RT NRT BE Frame rate (fps) Interarrival time (s) Interarrival time (s) Interarrival time (s) Type 1 2 0.500 12 12 Type 2 4 0.250 10 10 Type 3 6 0.166 8 8 Type 4 8 0.125 6 6 Type 5 10 0.100 4 4 Type 6 12 0.083 2 2 View Large Table 2. The simulation parameters. Parameter Value Surveillance area 400 × 400 Network size 100 nodes Simulation time 30 min Camera frame rate 2 to 12 fps Video frame size 1 to 10 kbits RT packet size 1 kbit NRT/BE packet size 200 Bits Packet interarrival time 2–12 s Bandwidth 250 kbps RT buffer size 50 kbits NRT/BE buffer size 4 kbits Queue weights (RT/NRT/BE) 0.7/0.2/0.1 Sleep rates (RT/NRT/BE) 5/40/60 % CW slot values (w1/w2/w3/w4/w5) 4/12/18/24/36 Parameter Value Surveillance area 400 × 400 Network size 100 nodes Simulation time 30 min Camera frame rate 2 to 12 fps Video frame size 1 to 10 kbits RT packet size 1 kbit NRT/BE packet size 200 Bits Packet interarrival time 2–12 s Bandwidth 250 kbps RT buffer size 50 kbits NRT/BE buffer size 4 kbits Queue weights (RT/NRT/BE) 0.7/0.2/0.1 Sleep rates (RT/NRT/BE) 5/40/60 % CW slot values (w1/w2/w3/w4/w5) 4/12/18/24/36 View Large Table 2. The simulation parameters. Parameter Value Surveillance area 400 × 400 Network size 100 nodes Simulation time 30 min Camera frame rate 2 to 12 fps Video frame size 1 to 10 kbits RT packet size 1 kbit NRT/BE packet size 200 Bits Packet interarrival time 2–12 s Bandwidth 250 kbps RT buffer size 50 kbits NRT/BE buffer size 4 kbits Queue weights (RT/NRT/BE) 0.7/0.2/0.1 Sleep rates (RT/NRT/BE) 5/40/60 % CW slot values (w1/w2/w3/w4/w5) 4/12/18/24/36 Parameter Value Surveillance area 400 × 400 Network size 100 nodes Simulation time 30 min Camera frame rate 2 to 12 fps Video frame size 1 to 10 kbits RT packet size 1 kbit NRT/BE packet size 200 Bits Packet interarrival time 2–12 s Bandwidth 250 kbps RT buffer size 50 kbits NRT/BE buffer size 4 kbits Queue weights (RT/NRT/BE) 0.7/0.2/0.1 Sleep rates (RT/NRT/BE) 5/40/60 % CW slot values (w1/w2/w3/w4/w5) 4/12/18/24/36 View Large In the simulation scenario, each node is able to generate RT, NRT and BE traffic. RT, NRT or BE packets which are generated according to the urgency situation have been added to the URT, UNRT and UBE queues. Each simulation was carried out 10 times with different seed values and the averages were taken. The simulation results of the urgMAC under varying network loads are presented in Fig. 4–7. Figure 4 presents the effect of TSM and ADM when no urgency occurs, Fig. 5 shows the effect of UCA and Fig. 6 presents the effect of TDC. In Fig. 7, comparative results are seen in the urgency scenario of the mechanisms developed when each node generates 10% urgent traffic. The average end-to-end delay results on the cluster head are given in comparison to the packets generated based on the parameters presented in Table 1. Figure 4. View largeDownload slide The effect of TSM and ADM. Figure 4. View largeDownload slide The effect of TSM and ADM. Figure 5. View largeDownload slide The effect of UCA. Figure 5. View largeDownload slide The effect of UCA. Figure 6. View largeDownload slide The effect of TDC. Figure 6. View largeDownload slide The effect of TDC. Figure 7. View largeDownload slide Transmitting urgent and non-urgent traffic together. Figure 7. View largeDownload slide Transmitting urgent and non-urgent traffic together. The average end-to-end delay results for the RT, NRT and BE traffic types as a result of the addition of TSM and ADM components in the WMSN MAC model based on the basic CSMA/CA scheme are presented in Fig. 4. The aim of TSM and ADM is to provide QoS support for the RT even if there is no urgent traffic. When the generated video traffic is at its maximum, the RT is transmitted with an average end-to-end delay of about 2 s lower than NRT and BE traffic. The average end-to-end delay results for the RT, NRT and BE traffic types as a result of the addition of TSM and ADM components as well as UCA is presented in Fig. 5. The aim of UCA is provide QoS support to RT adaptively by changing the CW value between the minimum and maximum values as shown in Fig. 3. With the addition of the UCA, the average end-to-end delay result of the RT has decreased slightly, but no significant difference has occurred since urgent traffic is not generated in this scenario. Figure 6 presents the average end-to-end delay results measured on the cluster head for RT, NRT and BE traffic types as a result of the addition of TSM, ADM, UCA components as well as TDC in the WMSN MAC model. The aim of the TDC is to provide QoS support to the RT traffic by changing the sleep–listen schedule according to the dominant traffic type on the node and also schedule more sleep time if the BE and NRT are dominant on the node to provide more channel usage chance to neighboring nodes with RT traffic. Even when the video traffic generated by the node is the largest, the RT is transmitted with a lower average end-to-end delay about 3 s from the NRT and about 8 s from the BE traffic. With the inclusion of the TDC and the sacrifice of package generation in the sleep period, a significant difference was found at the average end-to-end delay result of the RT. Figure 7 presents the average end-to-end delay results for RT, NRT, BE, URT, UNRT and BE traffic types as a result of the addition of TSM, ADM, UCA TDC and MMP components in the WMSN MAC model. Ten percent urgent traffic is generated in all nodes. Prioritization of urgent traffic classes and provision of QoS support in URT traffic have been observed in this scenario where all mechanisms are used together. When urgent traffic is generated, all of the urgent traffic classes are transmitted with relatively lower end-to-end delay values, as can be clearly seen in Fig. 7. However, the average end-to-end delay result value of URT is kept approximately constant in the range of 1.2–1.6 s. URT traffic is transmitted faster than RT. The URT also appears to have a lower average end-to-end delay result value of about 2.5 s from the UNRT and 3.49 s from the UBE. Performance of the urgMAC is evaluated and compared with SMAC, Diff-MAC and XL-WMSN. SMAC is the earliest contention-based WSN MAC protocol to adopt sleep–listen schedules and message passing mechanism, and Diff-MAC is the closest protocol to the urgMAC. MAC layer of the XL-WMSN framework has a duty cycle adjustment mechanism. It has a multi-queue packet classifier but does not provide any CW size adaptation scheme to prioritize these traffic classes. SMAC is used with a fixed duty cycle (DC) of 50% in comparisons. Since reducing average end-to-end delay result is the main goal of a QoS supported MAC protocol, Fig. 8 presents the average end-to-end delay results of real-time traffic classes for each protocol. The urgMAC, XL-WMSN and Diff-MAC prioritize the traffic classes and deliver the high-priority class with lower average end-to-end delay result. As the traffic load of the network increases, all UT classes of the urgMAC’s average end-to-end delivery performance become better owing to the use of UCA. NUT classes are too closed to the XL-WMSN’s and Diff-MAC’s results while ADM adjusts the data rate and UT classes maintain their stability. SMAC’s average end-to-end delay is acceptable but packet drop rate is high because of the static DC and single-queue architecture as seen in Fig. 9. Figure 8. View largeDownload slide Comparative average end-to-end delay results. Figure 8. View largeDownload slide Comparative average end-to-end delay results. Figure 9. View largeDownload slide Comparative average received traffic rate. Figure 9. View largeDownload slide Comparative average received traffic rate. Figure 9 presents the average received traffic-rate at the sink for the protocols. All protocols, except XL-WMSN, have MMP features. XL-WMSN, Diff-MAC and the urgMAC have traffic adaptation mechanisms but the urgMAC has ADM to maintain a nearly stable average received traffic-rate. The urgMAC achieves higher channel utilization rate. Figure 10 presents the average comparative energy consumption of the protocols for increasing traffic loads. In light traffic scenarios, energy consumption of the urgMAC is lesser than all protocols whereas it is lesser than the others except SMAC in heavy traffic scenarios. In a lighter traffic scenario, SMAC has the worst performance, but it keeps a low variation since it has a fixed duty cycle of 50%. All protocols, except SMAC, have duty cycle adaptation features. Those features increase active time of the sensor nodes when the offered traffic load is high for QoS provisioning. urgMAC consumes less energy than XL-WMSN and Diff-MAC in every scenario since its ADM adjusts the data rate. Figure 10. View largeDownload slide Average energy consumption comparison. Figure 10. View largeDownload slide Average energy consumption comparison. The proposed urgMAC is a QoS-aware cross-layer WMSN MAC protocol to provide QoS support for applications that contain specific urgency challenges. It takes precautions in order to save energy in non-urgent operating mode. The TDC of urgMAC adjusts the node’s active time according to the dominant traffic class and provides energy-savings during idle listening. The UCA reduces the number of collisions to decrease node energy consumption by adjusting the CW size adaptively. The main goal of urgMAC is rapid transmission of real-time multimedia and other sensed data from the nodes of target area in an urgency situation. As it can be seen from Fig. 10, urgMAC consumes more energy than SMAC in a very heavy traffic scenario. SMAC offers constant sleep–listen periods to increase network lifetime but it does not consider QoS support in a required manner. QoS-aware protocols are less likely not only to sleep but also to deliver QoS-required data packets fast in heavy traffic conditions. Figure 11 shows average energy consumptions and average end-to-end delay results together to highlight energy-delay tradeoff. The urgMAC outperforms Diff-MAC and XL-WMSN both in terms of end-to-end delay and energy consumption. As it is depicted in Fig. 11, urgMAC offers well above twice better performance than that of the SMAC in terms of end-to-end delay, although its performance slightly decreases in terms of energy consumption at high traffic loads. This tradeoff between the node energy consumption and end-to-end delay makes the urgMAC highly preferable for its use in real-time multimedia applications. Figure 11. View largeDownload slide Energy consumption and end-to-end delay results. Figure 11. View largeDownload slide Energy consumption and end-to-end delay results. 5. CONCLUSIONS This paper proposes a new traffic and QoS-aware cross-layer MAC protocol for WMSNs called urgMAC. The urgMAC includes mechanisms called TSM, ADM, UCA, TDC and MMP to provide QoS support for applications such as target detection, target tracking, border surveillance and battlefield monitoring, containing specific urgency challenges. These mechanisms have been developed, especially considering the needs of multimedia applications, in the context of cross-layer interaction and adaptive service quality concepts. The urgMAC has been modeled and evaluated by Riverbed Modeling and Simulation Software (OPNET). It is compared with the SMAC, Diff-MAC and XL-WMSN protocols from the literature, and it achieves better results for end-to-end delay and channel utilization parameters. As the traffic load of the network increases, it has been concluded that the average end-to-end delivery performance of all UT classes are better than NUT classes owing to use of the UCA. The UT classes tend to maintain a stable average end-to-end delay value since ADM adjusts the data rate. The future work will be coupling urgMAC with a QoS-aware routing protocol to test its performance for multimedia content delivery in an urgency scenario. The data rate adaptation coefficient might be further improved by adding more parameters such as collision estimation. ACKNOWLEDGEMENTS The authors would like to thank the editor and anonymous reviewers for their invaluable comments and suggestions. REFERENCES 1 Demirkol , I. , Ersoy , C. and Alagoz , F. ( 2006 ) MAC protocols for wireless sensor networks: a survey . IEEE Commun. Mag. , vol. 44 , 115 – 121 . Google Scholar Crossref Search ADS 2 Yigitel , M.A. , Incel , O.D. and Ersoy , C. 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For permissions, please e-mail: journals.permissions@oup.com This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model) TI - urgMAC: A New Traffic and QoS-aware Cross-Layer MAC protocol for Wireless Multimedia Sensor Networks JF - The Computer Journal DO - 10.1093/comjnl/bxx126 DA - 2018-10-01 UR - https://www.deepdyve.com/lp/oxford-university-press/urgmac-a-new-traffic-and-qos-aware-cross-layer-mac-protocol-for-BahfuzB4ed SP - 1460 VL - 61 IS - 10 DP - DeepDyve ER -