Survey of QoS routing protocols in Wireless Multimedia Sensor Networks <s> Quartet-Metric Link/Path Cost-Dependent Routing Protocols. <s> Many new routing protocols have been proposed for wireless sensor networks in recent years. Almost all of the routing protocols considered energy efficiency as the ultimate objective since energy is a very scarce resource for sensor nodes. However, the introduction imaging sensors has posed additional challenges. Transmission of imaging data requires both energy and QoS aware routing in order to ensure efficient usage of the sensors and effective access to the gathered measurements. In this paper, we propose an energy-aware QoS routing protocol for sensor networks which can also run efficiently with best-effort traffic. The protocol finds a least-cost, delay-constrained path for real-time data in terms of link cost that captures nodes' energy reserve, transmission energy, error rate and other communication parameters. Moreover, the throughput for non-real-time data is maximized by adjusting the service rate for both real-time and non-real-time data at the sensor nodes. Such adjustment of service rate is done by using two different mechanisms. Simulation results have demonstrated the effectiveness of our approach for different metrics with respect to the baseline approach where same link cost function is used without any service differentiation mechanism. <s> BIB001 </s> Survey of QoS routing protocols in Wireless Multimedia Sensor Networks <s> Quartet-Metric Link/Path Cost-Dependent Routing Protocols. <s> We investigate image and video transmission in camera-based wireless sensor networks (WSNs). Our objective is to design a mechanism that finds the transmission strategies that maximize the expected reconstruction quality of the transmitted data at the base station while making efficient use of the limited resources of the WSN. Our approach is based on quality-scalable coding and multipath transmission. Unlike conventional approaches where data is sent over the paths regardless of its importance at the destination, we propose a network-adaptive transmission mechanism that decomposes the source bitstream into segments of unequal importance and reserves the most reliable paths to transmit the segments with the highest importance. Moreover, we use unequal segment loss protection with erasure codes of different strengths to maximize the expected quality at the destination and propose a fast algorithm that finds nearly optimal transmission strategies. We also present simulation results using a test video sequence that show that the proposed transmission mechanism provides adaptability to the time and space varying conditions of camera-based wireless sensor networks. <s> BIB002 </s> Survey of QoS routing protocols in Wireless Multimedia Sensor Networks <s> Quartet-Metric Link/Path Cost-Dependent Routing Protocols. <s> The paper investigates the usefulness of multi-path routing to achieve lifetime improvements by load balancing and exploiting cross-layer information in wireless sensor networks. Performance gains in the order of 10-15 % could be achieved by altering path update rules of existing on-demand routing schemes. Problems encountered with concurrent traffic along interfering paths have been identified as a direct consequence of special MAC protocol properties. <s> BIB003 </s> Survey of QoS routing protocols in Wireless Multimedia Sensor Networks <s> Quartet-Metric Link/Path Cost-Dependent Routing Protocols. <s> The main purpose of a sensor network is information gathering and delivery. Therefore, the quantity and quality of the data delivered to the end-user is very important. In this paper, we focus on designing a general energy efficient, fault tolerant, and highly reliable routing protocol that prolongs the network lifetime; we call it SBRR (Score Based Reliable Routing). As the main objectives of this protocol are the reduction of packet loss and packet error, we select the best quality path of the network for highly reliable data transfer. The routing decision is based on a heuristic parameter named ‘Path Score’, which is a combination of four factors. These factors are relevant to hop count, energy level of sensors, error rate of links, and free buffer size of sensors for each path. Also our algorithm utilizes a disjoint backup path for every source; as a result, this reduces the risk of data loss and delivery delay. Simulation results reveal that the proposed algorithm yields a longer network lifetime, less packet latency, and higher delivery ratio than other existing schemes. <s> BIB004 </s> Survey of QoS routing protocols in Wireless Multimedia Sensor Networks <s> Quartet-Metric Link/Path Cost-Dependent Routing Protocols. <s> in this paper we investigate multi-path transmission of video over Wireless Multimedia Sensor Networks (WMSNs). Our objective is to provide a transmission mechanism to improve the video quality perceived at the receiver while considering energy, bandwidth and delay constraints of the network. Our approach is based on packet and path priority scheduling in multipath video transmission over WMSN. Video packets are classified according to their types and more important packets are transmitted through paths with better conditions. Path conditions are evaluated by a score mechanism using variant parameters such as free buffer size, energy, hop count and packet loss. Since path conditions are changed over time, our proposed scheme updates path conditions and adapting packet scheduling accordingly. Simulation analysis of the proposed video transmission scheme shows its efficiency in increasing perceived video quality at the receiver. <s> BIB005 </s> Survey of QoS routing protocols in Wireless Multimedia Sensor Networks <s> Quartet-Metric Link/Path Cost-Dependent Routing Protocols. <s> As a multimedia information acquisition and pro-cessing method, wireless multimedia sensor network(WMSN) has great application potential in military civilian. Compared with traditional wireless sensor network, the routing design of WMSN should obtain more attention on the quality of transmission. This paper proposes a reliable routing based on energy prediction (REP), which includes energy prediction and power allocation mechanism. The introduced prediction mechanism makes the sensor nodes predict the remaining energy of other nodes, which dramatically reduces the overall information needed for balancing energy. based on the predicted result, REP can dynamically balance the energy consumption of nodes by power allocation. The simulation results prove the efficiency on energy equilibrium and reliability of the proposed REP routing. <s> BIB006 </s> Survey of QoS routing protocols in Wireless Multimedia Sensor Networks <s> Quartet-Metric Link/Path Cost-Dependent Routing Protocols. <s> As a multimedia information acquisition and processing method, wireless multimedia sensor network(WMSN) has great application potential in military and civilian areas. Compared with traditional wireless sensor network, the routing design of WMSN should obtain more attention on the quality of transmission. This paper proposes an adaptive reliable routing based on clustering hierarchy named ARCH, which includes energy prediction and power allocation mechanism. To obtain a better performance, the cluster structure is formed based on cellular topology. The introduced prediction mechanism makes the sensor nodes predict the remaining energy of other nodes, which dramatically reduces the overall information needed for energy balancing. ARCH can dynamically balance the energy consumption of nodes based on the predicted results provided by power allocation. The simulation results prove the efficiency of the proposed ARCH routing. <s> BIB007 </s> Survey of QoS routing protocols in Wireless Multimedia Sensor Networks <s> Quartet-Metric Link/Path Cost-Dependent Routing Protocols. <s> Wireless Multimedia Sensor Networks (WMSN) have an increasing variety of multimedia based applications including image and video transmission. In these types of applications, multimedia sensor nodes should ideally maximize perceptual quality and minimize energy expenditures in communication. To obtain the required perceptual quality, quality of service (QoS) support is needed at the network level. However, mapping the network parameters to the end-user's perceptual quality measures during building paths is a challenging task due to incomplete identification metrics. In this paper, we propose Image Quality Aware Routing (IQAR) for WMSN that introduces the concept of image quality awareness by considering energy issue. The proposed approach employs intra-image prioritization and an adaptive path selection scheme that adjusts reliability level during image transmission using a distortion prediction model. <s> BIB008 </s> Survey of QoS routing protocols in Wireless Multimedia Sensor Networks <s> Quartet-Metric Link/Path Cost-Dependent Routing Protocols. <s> The transmission of video and imaging data in Wireless Multimedia Sensor Networks (WMSN) requires both energy efficiency and QoS assurance, in order to ensure the efficient use of sensor resources, an Ant Colony Optimization based QoS routing model is proposed to improve the routing protocol of WMSN. Firstly, a routing model for WMSN QoS was presented and then a routing algorithm ACOWMSN was brought forward, which uses the network restrict condition to update the pheromone concentration. The forward ants collects QoS parameters, and the backward ants carry QoS information to update the local node status during returning to source node. The simulation results show that the algorithm has better performance than the traditional QoS routing protocol and can significantly improve the network lifetime. <s> BIB009 </s> Survey of QoS routing protocols in Wireless Multimedia Sensor Networks <s> Quartet-Metric Link/Path Cost-Dependent Routing Protocols. <s> As a new multimedia information acquisition and processing method, wireless multimedia sensor network (WMSN) has great application potential and attracts more and more attentions. Compared to traditional wireless sensor networks, the routing design of WMSN has higher requirements on the quality of service (QoS). This paper systemically analyzes the similarity between social network and WMSN, then designs a QoS trust estimation model based on social network analysis, which enables each sensor node measuring the service quality by monitoring the behaviors of neighbor nodes. An energy efficient QoS assurance routing based on cluster hierarchy (EEQAR) is proposed to achieve energy efficiency and meet the requirement of QoS. To obtain a better performance, EEQAR routing adopts cellular topology to form the cluster structure and balance the energy consumption by structure movement. The simulation results show the high performance of EEQAR routing in lifetime and quality of service. <s> BIB010 </s> Survey of QoS routing protocols in Wireless Multimedia Sensor Networks <s> Quartet-Metric Link/Path Cost-Dependent Routing Protocols. <s> This paper presents an Adaptive Greedy-compass Energy-aware Multipath protocol (AGEM), a novel routing protocol for wireless multimedia sensors networks (WMSNs). AGEM uses sensors node positions to make packet forwarding decisions. These decisions are made online, at each forwarding node, in such a way that there is no need for global network topology knowledge and maintenance. AGEM routing protocol performs load-balancing to minimize energy consumption among nodes using twofold policy: (1) smart greedy forwarding, based on adaptive compass and (2) walking back forwarding to avoid holes. Performance evaluations of AGEM compared to GPSR (Greedy Perimeter Stateless Routing) show that AGEM can: (a) maximize the network lifetime, (b) guarantee quality of service for video stream transmission, and (c) scale better on densely deployed wireless sensors network. <s> BIB011 </s> Survey of QoS routing protocols in Wireless Multimedia Sensor Networks <s> Quartet-Metric Link/Path Cost-Dependent Routing Protocols. <s> Wireless Multimedia Sensor Networks (WMSN) are new and emerging networks of wirelessly connected devices, which consist of cameras, microphones, infra-red sensors, scalar sensors and others. These networks are fast gaining popularity due to their potential to be incorporated in various applications, such as, traffic monitoring, border surveillance, smart homes, environment and habitat monitoring, to retrieve heterogeneous data from the environment. However, these networks present many challenges as they are highly sensitive to delay and errors. The paper presents a Cross-layer QoS Routing protocol for WMSNs (CR-WMSN) that is aimed at providing soft end-to-end delay guarantees. Evaluation of this protocol shows that it provides better delay guarantees as compared to minimum hop routing protocol. <s> BIB012 </s> Survey of QoS routing protocols in Wireless Multimedia Sensor Networks <s> Quartet-Metric Link/Path Cost-Dependent Routing Protocols. <s> Wireless Multimedia Sensor Networks (WMSNs) is a novel information acquiring and processing technology which is more competent than traditional sensor networks in transferring and processing of huge amount of multimedia information data, such as audio, video, images and so on. It plays critical role in application in civil, military and commercial fields. In this paper, a Non-control sorting method is used to construct the Pareto optimal routing path set and the multiple attribute decision making method is adopted to search for the best routing path from the Pareto optimal routing path set. The simulation experiment result shows that our method can increase the probability of finding the optimal routing path, the TOPSIS method which is based on the Multiple Attribute Decision Making method obtains the best routing path from the Pareto Optimal routing set. <s> BIB013 </s> Survey of QoS routing protocols in Wireless Multimedia Sensor Networks <s> Quartet-Metric Link/Path Cost-Dependent Routing Protocols. <s> In Wireless multimedia sensor networks (WMSNs), new metrics are required in order to accurately measure and evaluate link quality of nodes residing along a routing path comprehensively considering end-to-end delay, throughput and radio interference. Moreover, it is important to develop a routing algorithm that can find an optimal path to meet a QoS requirement based on the metrics. This study presents a QoS routing method taking into account congestion, which is aimed at minimizing end-to-end delay and increasing throughput. With a use of congestion control technique and least cost-based routing mechanism, the proposed routing method increases packet transmission rate whereas it reduces packet loss and delay. Ultimately, it contributes to longer network lifetime of sensor networks, which could result to offering better reliability of the network. <s> BIB014 </s> Survey of QoS routing protocols in Wireless Multimedia Sensor Networks <s> Quartet-Metric Link/Path Cost-Dependent Routing Protocols. <s> Multipath routing in wireless multimedia sensor network makes it possible to transfer data simultaneously so as to reduce delay and congestion and it is worth researching. However, the current multipath routing strategy may cause problem that the node energy near sink becomes obviously higher than other nodes which makes the network invalid and dead. It also has serious impact on the performance of wireless multimedia sensor network (WMSN). In this paper, we propose a pair-wise directional geographical routing (PWDGR) strategy to solve the energy bottleneck problem. First, the source node can send the data to the pair-wise node around the sink node in accordance with certain algorithm and then it will send the data to the sink node. These pair-wise nodes are equally selected in 360° scope around sink according to a certain algorithm. Therefore, it can effectively relieve the serious energy burden around Sink and also make a balance between energy consumption and end-to-end delay. Theoretical analysis and a lot of simulation experiments on PWDGR have been done and the results indicate that PWDGR is superior to the proposed strategies of the similar strategies both in the view of the theory and the results of those simulation experiments. With respect to the strategies of the same kind, PWDGR is able to prolong 70% network life. The delay time is also measured and it is only increased by 8.1% compared with the similar strategies. <s> BIB015
Many routing schemes formulate routing decisions based on a combination of four routing metrics. Such schemes which determine link/path cost with the proper blend of four metrics are categorized as quartet-metric link/path cost-dependent routing scheme. Under this category, a comparative summary of routing schemes surveyed is shown in Table 4 . Akkaya and Younis presented energy-and QoS-aware routing support for both real-time and best-effort traffic simultaneously BIB001 . Path selection is based on four metrics, namely, distance, residual energy, link error rate with respect to the neighboring node, and end-to-end delay of an entire path. It can find multiple paths by using first three metrics along with an extended Dijkstra's algorithm. Further, optimal path satisfying an end-to-end delay constraint is selected. To support both real-time and nonreal-time traffic, a class-based queuing model is adapted. According to this model, every node consists of a classifier and a scheduler. The classifier places every incoming packet in an appropriate queue, and the scheduler decides the priority of every outgoing packet based on bandwidth ratio. This protocol maximizes throughput for real-time traffic and guarantees best-effort data traffic. However, in order to explore multiple paths, complete knowledge of network topology is required at the base station. In addition, link bandwidth is not shared after the initial allotment. GEAMS is an online geographic energy-aware multipath stream-based routing protocol  . The forwarding policy at each node is based on four different metrics, namely, remaining energy, the distance between the current node and its neighbor, current stream history, and a number of hops from source to the current node. It consists of two types of forwarding modes: smart greedy forwarding and walking back forwarding. This protocol being online, every sensor node is regularly updated by its neighboring nodes about distance, link status, and remaining energy. In smart greedy forwarding mode, a list of best neighbors is selected based on an objective function. Based on this function score, packets with small and large hop count are forwarded to the worst neighbor node and the best neighbor node, respectively. Walking back forwarding mode is used recursively in the case of unavailability of the closest neighbor node to the sink. GEAMS is further extended in AGEM, which uses an adaptive greedy-compass forwarding policy to select the best neighbor BIB011 . AGEM chooses nodes with the smallest angular offset from a virtual line toward the sink that satisfies a minimum number of nodes ( ≥ 2) to guarantee multipath routing. If the above criteria are not satisfied, then angle ( ) is incremented in small steps toward 180 ∘ . If < 2 at = 180 ∘ , then walking back forwarding mode is executed. Both GEAM and AGEM are ideal choices for WMSNs; they ensure load balancing, delay, and packet loss constraint. However, in less dense network scheme performance is not satisfactory and does not consider traffic priority. S-AOMDV is a multipath video transmission technique which is an extension of previous work BIB002 BIB003 BIB004 . This technique is based on packet priority and path scheduling BIB005 . Packets are given priority based on the type of frame (I, P, or B frame). Path selection depends on path-score, which is calculated from four metrics, namely, residual energy, free buffer size, hop count, and packet loss rate. At each sensor node, three queues are used separately for each type of frame. When the required transmission rate is greater than the available rate, then the source drops a few packets to maintain distortion at a minimum level. Significant packets are transmitted over more reliable paths, resulting in excellent video quality at the receiver. However, S-AOMDV requires higher bandwidth and consumes more energy in case of multiple sources. REP is reliable routing based on a self-adaptive power allocation and energy prediction mechanism BIB006 . Path selection depends upon four metrics, namely, remaining energy of a node, average remaining energy of all nodes on a path, reaching probability, and reliability requirement. The transmission power of a sensor node is varied to eight different levels based on the remaining energy of that node which, in turn, balances network lifetime. In the energy prediction mechanism, every sensor node calculates energy consumption of its own and other nodes. Calculation of energy consumptions of other nodes depends on seven working states, namely, sleep, sense, idle, receive, transmit, process, and access. The entire network is separated into several concentric coronas to ensure that all sensory data reach the sink node. The results show that REP along with energy prediction and power allocation is more reliable and energy efficient. However, at high transmission power levels REP may suffer from intrapath interference. The concept of REP is further explored in ARCH for cluster-based adaptive reliable routing BIB007 . The cluster structure used is a cellular topology consisting of equal-sized virtual cellular cells. The topology supports multihop routing in single clusters and intercluster, whereas multipath routing is supported only in intercluster. Similar to REP, this technique may also suffer from intrapath interference. The results of ARCH are not compared with any other protocols. IQAR is an adaptive routing protocol designed to transmit low-resolution images on WMSNs BIB008 . Based on entropy or edge, every image is assigned a high or low priority before transmission. Next hop selection is based on a cost function, which depends on link quality (PDR), delay, remaining energy, and reliability requirement. The end-to-end delay is maintained with the help of desired delivery speed. Based on average cost and required speed, all neighboring nodes are classified into two categories, namely, high-quality neighbor nodes and low-quality neighbor nodes. From the set of highquality neighbor nodes, it chooses the next hop node with the highest cost and that meets reliability requirements. With respect to energy, delay, and image quality, IQAR shows better performance than MMSPEED. However, in IQAR, prioritization is limited to only images; that is, prioritization is not applicable for scalar data, audio data, or video data. In addition, relatively IQAR performance is not satisfactory when a number of flows are less. ACOWMSN is an Ant Colony Optimization based QoS routing algorithm that considers four QoS metrics during the route discovery process, namely, bandwidth, delay, packet loss rate, and remaining energy BIB009 . Selected link or path should satisfy all four routing constraints. It optimizes the final route based on the hop count of the path. It uses two types of artificial ants, namely, forward ants and backward ants. The source node broadcasts forward ants. Intermediate neighboring nodes that satisfy the requirements of these fourQoS metrics will again broadcast these forward ants. When a forward ant reaches a sink, it converts into a backward ant and returns to the source node in the opposite direction along the same path. A backward ant updates the pheromone concentration value of each node. Though exhibits many properties for WMSNs routing, ACOWMSN generates heavy traffic in the form of ants, which is not suitable for very large networks. However, it is relatively more scalable and reliable than the other ant colony optimization based schemes. EEQAR is energy-efficient QoS assurance hierarchical routing for WMSNs BIB010 . The next relay node is selected based on four metrics, namely, remaining energy, trust value, data correlation coefficient, and hop count of the neighboring node to the cluster head. Based on these four parameters, each node stores an optimization factor table. The concept of trust value metric is derived from social network analysis in which trust value is estimated by monitoring directly or indirectly the current and past behavior of neighboring nodes. A data correlation coefficient is used for data fusion to reduce the amount of data transmission. After every round, the cluster structure is modified by giving mobility to the cluster head which avoids creation of network holes and balances energy consumption. EEQAR improves network lifetime over ARCH BIB007 , but its dependence on high transmission power level may cause interference in the nearby nodes. CR-WMSN is a reactive, cross-layer QoS routing protocol that guarantees end-to-end delay BIB012 . A selection of the next hop is based on four metrics, namely, PST, hop count, channel utilization, and remaining energy of a node. Channel utilization signifies intensity of contention around the node. During route discovery, CR-WMSN selects nodes with a smaller PST and low contention, which reduces congestion and increases throughput. The length of another path should not be more than three hops longer than the shortest path (other path lengths ≤ shortest path length + 3 hops). This constraint on the length of the path restricts further load balancing and the lifetime of the network. Simulation results show that CR-WMSN guarantees end-to-end delay and higher throughput. Work by Dong et al. based on the genetic algorithm finds the best routing path from the set of Pareto-optimal routing paths BIB013 . These paths are found with a multiobjective function that is based on four metrics, namely, bandwidth, delay, jitter, and packet loss rate. A set of Pareto-optimal routing paths is found with the help of a noncontrol sorting method. From this set, the best path is found by using the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS). In TOPSIS, each path is compared with an ideal best solution and worst solution. Compared with previous schemes using genetic approach, this scheme shows an increase in the probability of finding the best optimal path, though optimal path is completely dependent on the construction of Pareto solution set. Another routing scheme by Bae et al. provides congestion control, minimizes delay, and maximizes throughput BIB014 . The optimal path is determined using four metrics, namely, traffic priority, link quality, residual energy, and the distance between nodes. Every node will calculate its priority with respect to sink. Based on this priority and other metrics each node will find two forwarding nodes, namely, main forwarding node and alternate forwarding node. Congestion is identified using buffer occupancy and congestion degree of a node. Alternate node is used when congestion occurs at the main forwarding node. Three types of traffic priorities are defined for packets, that is, green, yellow, and red. The green packet has the highest priority whereas red packet has the lowest priority. Contrary to the claim, results regarding graphs are not shared by the authors. Overhead is more due to two reasons, that is, first, every node that is required to calculate priority with respect to sink and second sharing of buffer and congestion degree information with each other. Pair-Wise Directional Geographical Routing (PWDGR) solves energy bottleneck problem around sink and source BIB015 . Next forwarding node is decided based on a number of hops, 1-hop distance, path contract angle, and included angle. Neighbor Nodes selected in the 360 ∘ scope around sink node are called as pairwise nodes. All pairwise nodes are used to prolong the network lifetime. Similarly, source neighbor nodes known as source cooperative nodes are selected by considering energy consumption problem in optimized order. Multiple paths in PWDGR help fast bandwidth aggregation, load balancing, and better video quality at the sink. Compared to a dense sensor network, performance of PWDGR diminishes in low-density network. This can be attributed to the availability of very few pairwise nodes in low density network.