Moreover, the simulation results show how incorporating WEMPPs improved the performance of different routing protocols. It has at least two interfaces: a wired one and a wireless one. In order to understand how WEMPP works, we differentiate its operation under the following circumstances:. By setting the previous procedures in the WEMPP nodes, our solution promotes using a wired segment even for connecting two wireless nodes in the same network. The wired segment is more reliable and provides a higher bandwidth than wireless links. Here, mesh node 1 sends a frame to mesh node 2 without knowing any wireless route to mesh node 2.
One of the biggest advantages of using WEMPP is that it allows a WMN to reduce the number of hops between the source and destination while the interferences supported by the wireless medium can be decreased. As mentioned earlier, the number of interferences, contentions and collisions increases as the number of hops between two nodes increases.
Thus, the WEMPP framework reduces the number of lost packets and, in turn, allows a better video quality on mesh nodes, for instance. With WEMPP communications are supported by shorter paths, therefore, it is possible to increase the network density without significantly increasing the interferences in the system. The convenience is determined by the routing metric so no all intra-traffic necessarily traverses the Ethernet.
Another advantage of the proposed solution is that it can be implemented without any changes in the upper OSI Open System Interconnection layer protocols.
Furthermore, WEMPP allows nodes in different sub-clusters to communicate with each other and move from one sub-cluster to another without requiring any reconfiguration in the node. The proposed solution does not modify the functions of the IP layer. WEMPP was carefully implemented in the simulator to show how it can improve the performance of the existing routing protocols without changing their algorithms or functions.
Changes in a routing protocol are costly and they often bring along new challenges. It was originally designed for building network simulators including wired and wireless communication systems, queuing networks, on-chip networks and so on. The simulation parameters and results are presented and discussed in the following sub-sections. Specifically, we evaluate how different routing protocols perform when WEMPPs are incorporated into the wireless mesh networks.
The simulation parameters and their values are summarized in Table 1. A video server, placed as a node, distributes seconds of live video stream [ 33 ] to the network. The red areas represent the obstacles, and the lines represent the pathways. WEMPPs, marked by ellipse, are connected to each other using solid lines wired links. When a node reaches a border, it stops, turns and continues in the opposite direction.
We assume that mesh nodes are in high speed vehicles such as cars and motorbikes with their movements restricted by the road Fig. Moreover, the assumption is that all pedestrians i.
All STA nodes, i. In addition, some MSNs request video traffic from the video server. MSNs are randomly selected from the pool of existing mesh nodes. As shown in Table 1 , the number of MSNs changes based on the number of existing mesh nodes in the network. The goal of simulation was to examine how some well-known routing protocols intended for wireless mesh networks cope with WEMPPs. We disabled the path accumulation feature in DYMO in its reactive mode. Therefore, its behavior is similar to that of AODV which is a reactive routing protocol. Moreover, DYMO has been employed as the basis to model a spanning tree routing protocol.
In this case, the root sends a Route Request packet which will be broadcasted by the intermediate nodes and will be immediately answered with a Route Reply. Table 2 provides detailed information about the routing protocols used for simulation. These routing protocols run in the link layer.
This is done by examining the following five variables:. The video stream has a G16B1 structure in which each Group-of-Pictures includes 16 frames. The frame frequency is 30 per second and the rate of MSN changes from 10 to percent of mesh nodes in increments of To examine the efficiency of WEMPP in live video streaming, we ran the simulation 5 times and calculated the average values of each variable of interest Figs.
In these figures, no aggregation means that each packet includes only one or a part of one video frame while aggregation mode means each packet can contain more than one video frame.
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Similarly, MSN showed These results clearly show how WEMPP increases video quality on nodes, because they can buffer more number of video packets before their playback times. HWMP routing protocol cannot provide good performance when there are mobile nodes in the network [ 7 ].
As the result, these nodes can receive the required video packets in proper time which leads to less video distortion. MSN also showed Node mobility can noticeably affect the performance of proactive protocols. However, WEMPP addresses this problem by efficiently routing the video packets among nodes using a wired segment which is not degraded by mobility Fig. In summary, Figs. Although Figs. In other words, STA and mesh nodes averagely experience When a node receives more video frames, the probability of playback skip due to frame dependency sharply decreases [ 37 ].
Routing overhead is improved by On the other hand, routing overhead is increased by Proactive imposes higher routing overhead, because there are more nodes that are neighbors when WEMPP is used. In fact a greater number of neighboring nodes translates to larger OLSR packets.
So smaller messages in size are exchanged. Video distortion is an important indication of the quality of live video streaming. Based on Fig. Given its importance, we measured video distortion in two cases. In the first case, aggregation was not used in the network, i. In other words when aggregation method was not used in the network, WEMPP reduced video distortion by The aforementioned results mean that on average video distortion was reduced by The fact is more packets can be generated and exchanged in the network when aggregation method is not used.
With more packets in the network, the traffic and in turn the number of collisions will increase too. In this study, we introduced WEMPP as an efficient engineering solution to resolve some of the most significant problems in WMNs, namely reduced bandwidth, poor communication and low scalability. WEMPPs are special elements with wireless and wired interfaces that promote the use of wired links even for intra-traffic where the source and destination of the traffic within the same network.
Particularly, WEMPPs are connected through an Ethernet, which is characterized by a higher bandwidth than the wireless medium. WEMPPs are carefully designed so that they can be employed by other elements of the network without the need for any change in their functionality. We showed that regardless of the used routing protocol and the type of distributed video stream, WEMPP improves the network performance by reducing the end-to-end delay, the packet delay variation, and the routing overhead.
The aforementioned changes increase the total number of successfully received video packets TSRP and, consequently, reduce video distortion. Moreover, WEMPP attenuates the detrimental effect of having multiple mesh source nodes on the perceived video quality. Our results clearly show that employing WEMPP keeps the system in a more stable condition, and improves the dynamic behavior of the network due to the higher mobility rates of the nodes.
As a result, the perceived video quality on both STA and mesh nodes considerably improves. Furthermore, there is no need to change the functions of IP layer and routing protocols. In fact, WEMPP is an engineering solution that effectively improves the performance of the existing routing protocols without imposing additional costs. In our future work, we plan to implement a test-based experiment. We will measure the dynamic performance of the proposed solution e. Browse Subject Areas?
Click through the PLOS taxonomy to find articles in your field. Abstract Wireless Mesh Networks WMNs cannot completely guarantee good performance of traffic sources such as video streaming. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited Data Availability: All relevant data are within the paper.
Introduction A Wireless Mesh Network WMN consists of mesh routers and nodes that communicate by means of multiple wireless links [ 1 ]. Related Work In this section, we first analyze the limitations of the current transmission technologies. Technology Overview The purpose of our study is to connect two wireless nodes within the same network through wired links to provide a better performance than that offered by the wireless medium. Download: PPT.
Proposals supporting wired links for connecting wireless nodes Ariza-Quintana et al. Efficient Transmission of Broadcast Video Traffic Data communication using only wireless infrastructure leads to poor network performance due to the high number of interferences and collisions common to the wireless medium [ 17 , 18 ]. Problem Statement In the previous sections, we discussed some of the existing challenges in WMNs and the recently proposed approaches to address them. The most important challenges to exploit the wired links for intra-traffic can be classified as follows: The effects of using the multi-hop technique on the perceived video quality on receivers in WMNs are considerable [ 25 ].
In fact the probability of packet loss, interference and collision increases as the number of hops between the source and destination increases [ 26 ]. It is worth noting that the packet loss considerably affects the performance of wireless networks [ 27 ], especially in video streaming applications.
Suppose L e is the packet loss probability on link e in a wireless network. In this equation the assumption is that there is no correlation among the losses in adjacent links. For simplicity, the probability of packet loss is considered to be the same in all links. Such simplification helps us to see that the probability of packet loss thoroughly depends on the number of hops. A simple method to reduce the number of hops between the source and destination is to increase the transmission power of nodes, and therefore, extend their coverage area [ 28 ].
However, the problem is that L e in a receiver node is correlated with the interferences provoked by other nodes.
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Interferences can be computed by: 2 where P i is the transmission power of node N i , U represents the set of nodes which can transmit in the same interval as node N i receives a packet, and A represents power attenuation and is a function of the distance between the nodes. Thus, incrementing the transmission power leads to greater interference which in turn results in higher probability of packet loss. For free space propagation, Equation 2 can be written as follows [ 29 ]. Mesh networks can relay messages using either a flooding technique or a routing technique.
With routing , the message is propagated along a path by hopping from node to node until it reaches its destination. To ensure that all its paths are available, the network must allow for continuous connections and must reconfigure itself around broken paths, using self-healing algorithms such as Shortest Path Bridging.
Self-healing allows a routing-based network to operate when a node breaks down or when a connection becomes unreliable. As a result, the network is typically quite reliable, as there is often more than one path between a source and a destination in the network. Although mostly used in wireless situations, this concept can also apply to wired networks and to software interaction. A mesh network whose nodes are all connected to each other is a fully connected network. Fully connected wired networks have the advantages of security and reliability: problems in a cable affect only the two nodes attached to it.
However, in such networks, the number of cables, and therefore the cost, goes up rapidly as the number of nodes increases. Shortest path bridging allows Ethernet switches to be connected in a mesh topology, and it allows for all paths to be active. Wireless mesh radio networks were originally developed for military applications, such that every node could dynamically serve as a router for every other node.
In that way, even in the event of a failure of some nodes, the remaining nodes could continue to communicate with each other, and, if necessary, to serve as uplinks for the other nodes. Early wireless mesh network nodes had a single half-duplex radio that, at any one instant, could either transmit or receive, but not both at the same time. This was accompanied by the development of shared mesh networks.
This was subsequently superseded by more complex radio hardware that could receive packets from an upstream node and transmit packets to a downstream node simultaneously on a different frequency or a different CDMA channel. This allowed the development of switched mesh networks.
Promoting Wired Links in Wireless Mesh Networks: An Efficient Engineering Solution
With the development of broadband wireless technologies, people expect wireless networks with higher data rate, higher spectrum efficiency, wider coverage, and more extensive service support. Such a continuous bandwidth is not available in existing bands. Higher working frequency and broader bandwidth are helpful for increasing data rate, but the coverage shrinks with the increase of frequency. Consequently, a contradiction arises between data rate and coverage, for which a trade-off is needed to balance them.
For example, in IEEE As a result, to achieve a high data rate in a wide coverage, lots of APs have to be deployed in the wireless networks. However, in practice, deploying a large amount of APs is quite difficult for two reasons: the cost is too expensive; and it is impractical to connect all APs into the wired backbone, especially in the regions without wired services.
They cannot provide services for the users until their central control units are connected to the backbone network. Therefore, to enable the wireless Mesh architecture in the entire network, the first thing is to solve the wireless implementation problem of the backbone . These Mesh nodes can make a full Mesh or a partial Mesh.
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In the full Mesh, any two nodes in the network can be directly connected, while in the partial Mesh, only some nodes can directly communicate with each other. It can be configured with one or several wireless interfaces, which are based on either the same or different wireless access technologies. Compared with traditional routers, Mesh routers can achieve the same coverage with lower transmit powers by way of multi-hops. Moreover, by enhancing its MAC protocol, a Mesh router can obtain a better scalability in the multi-hop Mesh network environment.
A Mesh client not only has a networking function, but also can act as a router, but it cannot play the role of a gateway or bridge. Besides, it can be configured with only one wireless interface and support one wireless access technology. Currently, there are two basic wireless Mesh architectures: infrastructure Mesh and client Mesh. In the hybrid Mesh architecture, clients can be connected to the backbone via Mesh routers, or can directly construct a Mesh network i.
Meanwhile, the routing function of the client can internally enhance the connectivity and coverage of the Mesh network. Cooperative relay is actually an extension of a single path relay. In which, one or several nodes with a common coverage area, called relay node s R, are added between the source node S and the destination node D, and the destination node D can combine the data from both the source node and relay nodes.
In this way, the pressure arisen from multiple antennas unable to be configured at the terminal is alleviated; Figure 3 shows an example in downlink, where the Base Station BS , Relay Station RS and User Terminal UT act as the source node, relay node and destination node respectively. In either type, the destination node combines the signals received in different timeslots to obtain spatial diversity gains. As signal information of multiple paths is used, spatial diversity gain is achieved at the destination node, thus the data rate and reliability of relay links are guaranteed.
But cooperative relaying technologies are implemented in Physical Layer to ensure data rate and reliability of relay links. Figure 4 illustrates the application of cooperative relaying technologies in a fixed wireless Mesh network . As shown in Figure 4, node C can combine the signals from node A and node B to achieve cooperative relaying, and to obtain spatial diversity gain as well. The cooperative relaying technologies can be used in any wireless relay link.