World Applied Sciences Journal 30 (7): 870-886, 2014ISSN 1818-4952© IDOSI Publications, 2014DOI: 10.5829/idosi.wasj.2014.30.07.1465

Correspoding Author: Mohammad Siraj, PSATRI, College of Engineering, King Saud University, P.O. Box: 800, Riyadh 11421870

A Survey on Routing Algorithms andRouting Metrics for Wireless Mesh Networks

Mohammad Siraj

PSATRI, College of Engineering, King Saud University, P.O. Box: 800, Riyadh 11421

Submitted: Nov 30, 2013; Accepted: Feb 10, 2014; Published: Feb 23, 2014Abstract: Wireless Mesh Network (WMN) is an emerging wireless technology for various futuristicapplications like video on demand, healthcare systems, disaster and emergency, modern intelligent transportsystems, public security systems, broadband internet for home and campus networking. Routing is an importantfactor for forwarding a data packet from source node to destination node.Wireless routing is totally differentthan routing in a wired network. Routing metrics are a crucial part of routing protocols affecting the performanceof wireless mesh networks (WMN). When the routing protocols are implemented, the routing metrics areallocated to various paths. Their job is to compute the best routing path. They are assimilated in routingprotocols to enhance WMNs efficiency in terms of reliability, latency, throughput, error rate and cost. Thispaper presents a survey of important routing protocols and routing metrics for WMNs.

Key words: Interference Routing protocol Routing metric Wireless Mesh Network

INTRODUCTION Generally, the mesh routers are static. Figure 1 shows anarchitecture of WMN.

IEEE 802.11 Multi Hop Wireless Mesh Network Routing metricsare very essential for calculation of(WMN) [1, 2] is a promising technology, seen as a the best quality path. It does so by capturing anpromising potential for Internet Service Providers (ISPs) accurately good quality link. Due to the presence of staticand other end-users to deliver a consistent wireless nodes and common wireless medium in WMNs designingbroadband service access and a robust network at a a good routing metric is challenging.To study the impactrational cost. They are now being seen as last few miles of a good routing metric design is a challenge forconnectivity. Wireless networks differ from wired researchers. To understand these challenges the currentnetworks. They can organize and configure themselves routing metrics which have been presented for WMNdynamically. i.e., establishment and maintenance of the protocols are analyzed and a comparison of theirnetwork is done automatically by the mesh nodes. This prominent features have been done for their advantagesautomatic establishment and maintenance has numerous and drawbacks.benefits for the end-users. Service coverage becomes The remainder of this paper is organized as follows.dependable and network is robust. Deployment and In section 2 important design requirements of an efficientmaintenance of WMN is easy and economical. Mesh mesh routing protocol are discussed. In section 3, thenetworks comprises of mesh clients and mesh routers. review of important routing protocols for WMNs haveThe end users can use WMN to access the internet by been discussed. Section 4 discusses the designconnecting to any of the routers.The client could be a requirements and characteristics of routing metrics.notebook, PDAs, desktop PCs or a mobile phone whereas Section 5 describes a review of important routing metricsmesh routers are a part of backbone. They differ from for WMNs followed by a conclusion.mobile ad-hoc network (MANET), as the problems inMANETs are caused by the absence of infrastructure and Requirements of an Efficient Mesh Routing Protocols:nodes mobility [3]. In WMNs connectivity between the An efficient mesh routing protocol should have themesh clients and mesh routers are through multiple hops. following features.

World Appl. Sci. J., 30 (7): 870-886, 2014

871

Fig. 1: Wireless Mesh Architecture [4]

Distributed: The protocol should be a distributed, as network size. This requires that control overhead shouldcentralized routing involves higher control in order to be minimized and routing protocol should be able to adapthave improved reliability. As node mobility is very to the network size. In [5, 6] researchers showed thatminimal, therefore, mesh networks prefer the decentralized scalability declines with the large number of users.routing protocol. Gupta and Kumar [7] computed per node capacity. The

Adaptable to Topology Changes: The algorithm should would be able to scale or not [8-10]. The networkadapt to minimal changes in the topology caused by coverage area results in an increase of load. In [11-13],node's mobility. This is a substitute to the uniformly showed how to keep the deterioration to a minimum level.distributed traffic within the network and needs The effect of physical layer on scalability was shown inmaintenance of the routing paths of all the nodes [14]. It was seen thatdirectional antenna increasescontinuously. performance and scalability [15-16]. Other researchers

Loop-Free: This is a fundamental requirement of any WMN.routing protocol to avoid unnecessary wastage ofbandwidth. In the mesh network, due to node mobility, Quality of Service (QoS): In WMNs, the quality ofloops may be formed during the route establishment. service (QoS) features requires a great amount ofSo a routing protocol should eliminate such loops. A challenge due to resource limitations and node movement.routing protocol should be loop-free in order to avoid Therefore, it is essential that QoS metrics are incorporatedwastage of bandwidth. in WMN routing protocols for route discovery and

Security: If the security doesn’t exist, then the routing is on end to end delay, bandwidth, Packet delivery ratioprotocol issusceptible to different types of attacks such and energy and mechanism overheads. Hence, it isas spoofing and redirect messages. To prevent such mandatory for WMNs to have a proficient routing andvulnerabilities, security schemes are required. QoS mechanism for supporting various applications.Cryptographic mechanisms are utilized to solve security The routing protocol should ensure the required level ofissues and prevent such attacks. quality of service and that too should also be in real time

Scalability: Scalability is the protocol capability to have focused their work to study and improve QoS inmaintain its performance with an increase of users and WMN.

topology of the network decides whether the network

[17-20] have also studied the effects on scalability on

maintenance to support end-to-end QoS. QoS main focus

to support current traffic. Some of the researchers [21-28]

World Appl. Sci. J., 30 (7): 870-886, 2014

872

Routing Protocols: The routing protocols can be number of hops for every destination. To avoid loops,categorized into proactive routing, reactive routing and DSDV uses sequence numbers. The routing updates arehybrid routing protocols. Some of the important protocols either event driven or time driven. Each node transmitsin these categories have been discussed below. routing table updates and its routing information to its

Proactive Routing Protocols: Proactive routing of updates are possible. The first one is full dump and anbroadcasts periodic HELLO messages, like traditional incremental update. In the full dump, the complete routingrouting in the internet, in order to determine the global information is carried and may require the number ofview of the network topology, which is useful when route Network Protocol Data Unit (NPDU). In contrast, onlyestablishments are needed. However, established routes, entries of available destinations with recent changeswhich are cached in each node might never be used. from the routing table are sent in the incremental update.This leads to wastage of network bandwidth, especially in When the nodes are relatively static, incremental updatehigh node density. In addition, in proactive routing avoids extra traffic compared to the full dump update.protocols, there is a trade-off between the freshness of However, the full dump update is more efficient in thecached routes and the frequency of message broadcasts. network with high speed mobile nodes. In both updateFrequent broadcast messages are useful in order for the mechanisms, the route update packet is sent with apacket carrier node to calculate efficient routes to the unique sequence number with the routing information.specified destination. However, this is at the expense of During the selection, the path having the greatesthigh bandwidth consumption, which grants the channel sequence number is selected as the current path. If twofor broadcast traffic. On the other hand, this type of paths have the same sequence number, the shortest pathrouting is suitable for real time applications (delay is selected. sensitive services) since the route between a pair ofsources and destinations is created beforehand. In other Optimized Link State Routing Protocol (OLSR):words, the source does not need to flood route discovery Optimized Link State Routing Protocol is built over therequests on demand as the route is established in the link state algorithm. In this protocol, information about thebackground. In spite of the low end-to-end latency of link state of every node is broadcasted to every otherpacket forwarding, the recovery of unused cached routes node of the network. In OLSR, all nodes keep a track ofwastes massive bandwidth, especially in high mobile the information of their two hop neighbors. HELLOenvironments. Few key examples of proactive routing messages are used by OLSR to get the information aboutprotocols are Destination-Sequenced Distance Vector the links. Multi Point Relays (MPR) is a vital feature of theRouting (DSDV) [29], Fisheye State Routing (FSR) [30], OLSR protocol to minimize broadcasting. Each nodeOptimized Link State Routing (OLSR) [31], Source Tree selects a set of MPR among its one hop bidirectional linkAdaptive Routing (STAR) protocol [32], HEAT Protocol neighbors to all other nodes those are two hops away.[33], Wireless Routing Protocol (WRP) [34], Mobile Mesh This set can change with timeand is specified by theRouting Protocol (MMRP) [35], Linked Cluster selecting nodes in their HELLO messages.Architecture (LCA) [36], Hierarchical State Routing Whenever a node transmits a message, all of itsprotocol (HSR) [37], Topology Dissemination based on neighbors receive the message. Only that MPR whichReverse-Path Forwarding routing protocol (TBRPF) [38], receives the message for the first time, transmits theDirection Forward Routing (DFR) [39] and Distributed message. Due to this, the overhead due to flooding isBellman-Ford Routing Protocol (DBF) [40]. In this paper minimized.only a few important proactive protocols are discussed. Two types of control messages are used by OLSR.

DestinationSequencedDistance Vector Routing Protocol messages are periodically sent. The TC messages can be(DSDV): Destination Sequenced Distance Vector Routing forwarded only by MPR hosts.Protocol is proactive unicast routing protocol. DSDV is The major advantage of OLSR over other proactivebased on traditional Bellman Ford algorithm. In DSDV, protocols is that it broadcasts its link state informationevery node maintains a routing table. Each entry in the rather than routing tables and messages can be deliveredrouting table keeps information of all likely node in any order due to the sequence number. This protocoldestinations in the network. It also keeps a record of the is good for large and dense networks.

adjacent neighbor nodes periodically. In DSDV, two types

They are HELLO and TOPOLOGY CONTROL (TC). TC

World Appl. Sci. J., 30 (7): 870-886, 2014

873

Fig. 2: MRP route establishment message sequence [9]

Mesh Networking Routing Protocol (MRP): Mesh Fish-Eye State Routing Protocol (FSR): In [30], theNetworking Routing Protocol (MRP) is a proactive authors developed an efficient link state algorithm thatprotocol. In this protocol, to connect to the internet every maintains the global knowledge of the network topologyclient chooses a gateway. In the eventuality of the node at each node and disseminates the local information tomoving away or breaking down of the gateway node a the direct neighbor nodes instead of the whole network.different gateway is selected. The entire traffic movement In FSR protocol, the updates of link state information varyto the internet is through the gateway. One of the with the distance.versions of Mesh Protocol is MRP On-Demand. Towards the destination. Figure 3 shows the basic

MRP on-demand (MRP-O) [41] is a purely on-demand operation of FSR. That is, every node defines a boundaryprotocol. This protocol uses the messages like Route around itself. The inner boundary is formed by the closerDiscovery Message (RDIS),Route Advertisement nodes and they receive the link state information with the(RADV), Registration Request (RREG), Route Check highest frequency, whereas the further nodes broadcastPackets (RCHK) and Registration Acknowledgment the update with lower frequency. Thus, the FSR protocol(RACK). The node which is intended to join the network exchanges the link state information frequently with thewill send RDIS to its neighboring user nodes to find the vicinity nodes and with lower frequency for the furtherway to the closest gateway. Here only the source node nodes. In this way, the nodes can get up-to-date link stateone-hop neighbors gets the message. The nodes information about the nearby neighbor nodes.receiving the RDIS message respond by sending a RADV Apparently, there is a trade-off between the reduction ofpacket containing the information about their current overhead and the staleness of the link state information,routes metrics. All the neighboring nodes will send the leading to suboptimal route selection.RADV packets with some random delay to avoidcollisions. If a new node joins the network, then all RADV Reactive Routing Protocol: The basic operation ofpackets will be stored by it. Once all the RADV’s have reactive routing protocols [42-44] is route discovery frombeen received, it will choose one or more upstream route source node to destination node and works in reverse toto perform routing. Figure 2 showsthe MRP route the on demand Topology-based routing. This routingestablishment message sequence. The metrics used for solution establishes a route when a node makes a requestthis protocol are hop-count, route stability, minimum to transmit packets to another node in the network.delay, maximum bandwidth and minimum packet loss. At this time, the node re-broadcasts the requested routeThe metrics used for this protocol are hop-count, route establishment to find the intended destination. When thestability, minimum delay, maximum bandwidth and destination receives the query (or the en-route nodesminimum packet loss. know the path to it), it responds to the source for route

World Appl. Sci. J., 30 (7): 870-886, 2014

874

Fig. 3: FSR protocol basic operation are forwarded hop-by-hop. Unlike other on-demand

establishment between source and destination. Whenever for neighbor detection, or link status detection in DSR.the source node wants to transmit data packets towards Therefore, DSR operates truly on demand to minimize thethe destination, it floods the network with route request routing overhead. The route maintenance mechanism ispackets. The destination sends a route reply message, initiated when a node cannot deliver packet to itsafter which the source sends the data packet to the next-hop node as shown in Figure 6. This node thendestination. The advantage of this approach is that it generates route error messages towards the source nodedoes not maintain unused routes and reduces bandwidth to find the most viable route as shown in Figure 7. Hence,overhead in the network. the broken link is removed from the route cache of the

Some of the important examples of reactive protocol source node.are Ad Hoc on Demand Distance Vector (AODV)protocol, Temporarily Ordered Routing Algorithm (TORA) Ad-Hoc On-DemandDistance Vector Routing Algorithmprotocol [45], Dynamic Source Routing (DSR) protocol (AODV): AODV is a reactive unicast routing protocol.[46], ABR (Associativity Based Routing) protocol [47], AODV protocol doesn’t deploy flooding. AODV does notLink Quality Source Routing Algorithm (LQSR) protocol store routing information of all the nodes, instead it just[48], Dynamic MANET on Demand (DYMO) [49], keeps information about the nodes falling on the activeLightweight Mobile Routing protocol (LMR) [50], route.Load-Balancing Curveball Routing (LBCR) [51], Scalable In AODV when a source node has data packets andLocation Update-Based Routing Protocol (ScrRR ) [52] intends to communicate with another node, it initiates theand Interference-Aware Load-Balancing Routing (IALBR) route discovery process in the network. As the source[53]. has no suitable route for the destination, it broadcasts the

Dynamic Source Routing Algorithm (DSR): Dynamic RREQ packet contains the address of the source node,Source Routing Algorithm (DSR) is the source based address of the destination node and broadcast id.routing protocol where the source records the sequence Broadcast id is an identifier that contains the most-currentof intermediate nodes in a data packet which is sent to the sequence number of the source and the destination node.destination. The basic operation of the protocol consists Each RREQ begins with the least Time to Live (TTL)of two phases, namely the path discovery and path value. The TTL value increments by 1 if the destinationmaintenance process. In DSR, a path discovery phase is node is not found.HELLO messages, are used to notifybegun when the source node without a valid path intends adjacent neighbor nodes.to transmit a data packet to the destination node. DSR Routing tables keep records for a specific period.applies the source routing strategy to broadcast a route A cache is maintained by each node. The cache keeps therequest message. This includes source id, destination id, entries of the received RREQs. The RREQ with thea route record with an empty list of addresses of all greatest sequence numbers is accepted and others areintermediate nodes and a unique request id towards the rejected. The cache also saves the return path. RREPdestination node. On receiving route request, an message is generated and is transmitted back to theintermediate node caches the route record. Figure 4 shows source node provided the sequence number of thethe construction of route cache during node discovery. destination node is equal to or larger. This can be seenA route reply message may be replied if the destination from Figure 9.

node is arrived. The destination node cache stores theroute record. Then it uses the cached path in the routerecord for the propagation of route reply back to thesource node as shown in Figure 5. Otherwise, if this nodeis not in the route cache of route request, it appends itsaddress to the route record and broadcasts the routerequest messages. To avoid the overhead, DSR optionallydefines the unique request id for each message in theroute discovery mechanism. In addition, these messages

driven algorithms, there are no proactive periodic probes

Route request (RREQ) message as shown in Figure 8.

World Appl. Sci. J., 30 (7): 870-886, 2014

875

Fig. 4: Constructing route cache during node discovery

Fig. 5: Route Reply

Fig. 6: Route Error between Node 5 and Node 8

Fig. 7: Route Error sent from N5 to N1

Link Quality Source Routing Algorithm (LQSR): Link LQSR allocates comparative weights to the linksQuality Source Routing Algorithm was designed by between the wireless meh nodes after the nodes haveMicrosoft Research Group for their Mesh Connectivity been detected. Besides allocating weights, for everyLayer (MCL). Through LQSR, the computers are probable link the bandwidth, loss and the channel areconnected to form a mesh network using WiMax or Wi-Fi. calculated. All the nodes are conveyed this information.The LQSR protocol is built on Dynamic Source Routing Depending on this information, LQSR uses Weighted(DSR). Cumulative Expected Transmission Time (WCETT)

World Appl. Sci. J., 30 (7): 870-886, 2014

876

Fig. 8: Broadcasting RREQ Packets

Fig. 9: Route of the RREP to the Source

routing metric to find the best routing path from source to Generally, TORA offers several routes from source tothe destination node. The path between two nodes may destination. TORA functions can be broadly classifiedbe one hop or more depending whether intermediate into three types, which are a) 1) route creation, 2)nodes exist or not between the source and the destination maintaining route and 3) removal of route. It uses heightnode. The route is amended accordingly if the optimal metric during route creation and maintenance to form apath between source and destination is modified. Directed Acrylic Graph. (DAG) fixed at destination.This amendment is done without interruption of the link Links are allocated on the basis of relative height of theamong the nodes. The LQSR protocol does not require neighboring nodes. Timing is very crucial in TORA asvery little administration like DSR protocol to function the height metric relies on link failure logical time.automatically. When TORA wishes to delete the routes, it broadcasts a

In LQSR, after a node gets a RREQ packet, a link clear (CLR) packet flooding the entire network to deletequality metric is appended for the link over which the the invalidated paths.packet is received. When the source node gets a RREP The messages move in a downward flow that is apacket, it contains information about link quality and from a higher height node to a lower height node.node. To get the information about link state, adjacent Discovery and updating of routes is through Query (QRY)nodes are broadcasted HELLO messages by LQSR. and Update (UPD) packets. The QRY packet circulatesThese messages are utilized to find out the quality of the over the network until it finds a node which is either thelink over which the message was got. destination node or has route information. A UPD packet

containing the node’s height is then broadcasted.Temporally-Ordered Routing Algorithm- (TORA): On getting the UPD packet each node sets its heightTemporally Ordered Routing Algorithm (TORA) is an on larger than the height mentioned in the UPD message.demand routing protocol. It is a distributed routing After setting its height higher, this node broadcasts itsprotocol. It is designed to reduce the communication own UPD packet resulting in many routes.overhead involved in adjusting to the changes whichoccur whenever there is a change in network topology. Hybrid Routing Protocol: Hybrid routing protocolsTORA's control messages are generally restricted to a combines the advantages of both reactive and proactivevery minor group of nodes. It ensures loop free routes. routing protocols for performance and scalability.

World Appl. Sci. J., 30 (7): 870-886, 2014

877

It provides a mechanism such that it implements proactive Zone Routing Protocol (ZRP): ZRP falls in the categoryrouting for the nearby and frequently used routes. The of a hybrid protocol having reactive and proactive routingreactive routing technique is used for far away nodes and characteristics. It creates routing zones based on theseldom used for data relay. They minimize proactive neighbor nodes hopping distance. There are two zonesrouting protocol control overhead and reduces the delay created by it. One is the inside zone also called Intra Zonein reactive routing protocol during the route discovery where the packets are sent to the peripheral nodes fromprocess. Examples of hybrid routing protocols are Hazy- the originating node and the other zone which is outsideSighted Link State Routing (HSLS) protocol [54], Zone zone also called Inter Zone from where the packet isRouting Protocol (ZRP) [55], Hybrid Ad-Hoc Routing delivered to the sink node. This is shown in Figure 10Protocol (HARP), Hybrid Routing Protocol for Large Scale below. The zones are formed from the origin node at twoAd-Hoc Networks with Mobile Backbones (HRPLS) [56] hops away.and Zone-based Hierarchical Link State routing (ZHLS) ZRP is created by two routing protocols, which are[57]. In this section only a few important hybrid protocols Intra-Zone Routing Protocol (IARP) [57], a proactiveare discussed. routing protocol used for intra zone and a reactive routing

Hazy-Sighted Link State Routing Algorithm (HSLS): used for Inter Zone, respectively. The path from origin toHazy-Sighted Link State Routing Protocol (HSLS) is one sink node is made by IARP. Generally, all the currentof the most efficient hybrid routing protocol for mesh proactive routing algorithms can be used as the IARP fornetworks. Cowing Foundation is involved in the ZRP. For the inter zone paths, it uses IERP to find thedevelopment of HSLS. Researchers at BBN Technologies route. The originating node generates a route request tocreated the HSLS routing protocol. The network is not peripheral nodes. Peripheral nodes check their zone forflooded by HSLS. HSLS features are built on reactive, the sink node. If the destination node is not a part of thisproactive and suboptimal routing methodology. By zone, the peripheral node appends its own address to therestricting link state updates in time and space domain, route request packet and forwards the packet to itsthe updates are combined and sent once thereby saving peripheral nodes. If the sink node is a member of its zone,transmission capacity. it generates a route reply packet on the reverse path back

In HSLS, two proactive algorithms are integrated. to the source. The originating node saves this path andThe algorithms are Near-Sighted Link-State Routing sends the route reply to the sink nodes.(NSLSR) and Discretized Link-State Routing (DLSR).NSLSR restricts the number of hops for the Design Requirements and Characteristics of Routingcommunication of routing information. DLSR restricts the Metrics: There are four key requirements of routingnumber of times a routing information may be metrics for ensuring a good performance. First of all, therecommunicated. The reactive routing is needed due to a should be route stability to guarantee that the network isfailed attempt in the usage of a nearby link. This causes stable. It means that the routing metrics should notthe expiry of the next timer, maybe to recover the change the route frequently. Secondly, WMNinformation in finding a substitute route. The reactive characteristics can be captured by the metric for ensuringrouting takes place when there is a failure to use a good performance is on the paths having least weights.neighboring link which causes the expiry of the next timer. Thirdly, for computing, the routing metrics should haveIt then tries to find another route. proficient algorithms with polynomial complexity to

The main aim is to measure the global network compute paths having the least weight. Lastly, the routingwastage. It includes transmitting route updates of metrics should precisely capture quality links and help ininefficient transmission routes. Researchers used calculating efficient paths while ensuring that routingarithmetical optimization technique to compute how much protocols do not create forwarding loops. For creating atime link state updates take to transmit and what is the routing metric some important components required arecoverage of nodes link state updating. Whenever there is number of hops, channel diversity and link quality. In aa broken connection, a local routing cache update is WMN, a good routing metric should address therequired. This is the reactive portion of the algorithm. following criteria. HSLS provides good scalability properties and createsgood routes in real time. The data transfer and routing Intra-Flow Interference: Intra-flow interference takesinformation are distributed, so it provides good reliability place due to the interference of adjacent nodes on theand performance. same routing path. They compete against each other for

protocol called Inter-Zone Routing Protocol (IERP) [57],

P

O

SOriginating Node

Sink Node

Intra ZoneInter Zone

Peripheral Node

World Appl. Sci. J., 30 (7): 870-886, 2014

878

Fig. 10: An example of ZRP Protocol

Fig. 11: Intra-flow interference [58]

utilizing the channel. This intra-flow interference causes Figure 12 shows inter-flow interference because of thethroughput to degrade severely due to the consumption two paths namely 1 4 3 and 5 6 7. A good inter-flowof the flow bandwidth across every node on the same aware metric should assign a low weight 1 2 3 then torouting path. The Hop-Count of the flow increases with 1 4 3 as path 1 2 3 has less inter-flow interference.an increase in the end to end delay. This causescongestion. For example, in Figure 11, it is shown that the Load Balancing: It is defined as the capability of a routingpath 1 2 3 causes intra-flow interference because of the metric to balance the traffic load so that overloading ofreuse of channel 1 on the flow 1 2 and from 2 3. So the gateways in wireless mesh networks can be avoided andpath 1 4 3 does not have intra-flow interference as two the network resources are used fairly. WMNs are differentdifferent channels are assigned between 1 4 and 4 3. than other wired and wireless networks. The environmentIt can be said, that 1 4 3 is a better path in comparison to of the shared channel, presence of stationary mesh node,1 2 3. So a good intra-flow aware interference metric traffic routing pattern from the user to gateway node andshould assign 1 4 3 a lower weight than 1 2 3. In other the usage of multi radios distinguishes them from otherwords, a good routing metric reduces inter-flow networks. This unique characteristics and unbalancedinterference by selection of different channels for load in WMN causes load balancing problem. Loadneighboring nodes coming on the same path. balancing problem becomes an important issue in WMN

Inter-Flow Interference: Inter-flow interference occurs the traffic in WMNs is directed towards the Internetdue to the other flows operational on one particular gateway. This may result in an increase in traffic load onchannel and nodes are contending for that channel. some path which are connected to the internet gateway.This is caused by the multiple flows between different Due to the unbalanced load, channel overloading,routing paths as shown in Figure 12. This consumes the gateway overloading and center loading may occur.bandwidth of the nodes which are on this route. Channel overloading occurs when some of the channelsFurthermore, it competes for bandwidth occupation with are overloaded as compared to other channels. Centerthe neighboring nodes. In comparison to intra-flow loading occurs when the nodes at the centre of theinterference, inter-flow interference is harder to control network topology are used more during the traffic flowdue to the involvement of multiple flows and routes. as they fall on the shortest path. The traffic is oriented

as the volume of the network traffic is very high. Most of

World Appl. Sci. J., 30 (7): 870-886, 2014

879

Fig. 12: Inter-Flow interference [59]

towards the gateways as the traffic is routed through Routing Metrics: It is a recognized fact that routingthem. Due to the heavy traffic volume, congestion may metrics are a crucial part affecting the performance ofoccur. The focusing of traffic on gateway causes a drop wireless mesh networks (WMN). When the routingin the packets due to the overflow in the buffer. This protocols are implemented, the routing metrics aredropping of packets is unfavorable for the network to be allocated to various paths. Their job is to compute theefficient. This is called gateway overloading. best routing path. They are assimilated in routing

Thus, there is a critical need to avoid congestion due protocols to enhance WMNs efficiency in terms ofto the unbalanced load. This can be done by load reliability, latency, throughput, error rate and cost.balancing at different gateways and on the paths leading Routing metric is very essential for calculation of theto the gateway. Congested links should be avoided by best quality path. It does so by capturing ansegregating congested links from the new paths to have accurately good quality link. To study the impact of aload balancing. Load balancing and interference are good routing metric design, is a challenge for researchers.related. So to solve the problem of unbalanced load, To understand these challenges the current routinginterference problem should also be examined. metrics which have been presented for WMN

Isotonicity: It is defined as the characteristic of the prominent features have been done for their advantagesrouting metric by which it ensures that the order relation and drawbacks.between the weights of any two paths is conserved ifboth are preceded by a third path which is common to the Hop-Count Metric: The most common metric used in thetwo paths. For example, if W (p) is the weight which is the multi-hop routing protocols is Hop-Count metric. It isfunction along the path p and W (q) is the weight which used in protocols like DSDV, DSR and AODV. Hop-Countis the function of path q, isotonicity can be defined as: A metric finds route having the minimum number of hops.routing metric is isotonic if the quadruplet (A, , W, ) is Hop-Count can outclass other metrics, which areisotonic and if W (p) W (q) implies W(r p) W(r q) dependent on load in high agility situations. This showsas shown in Figure 2.10. its agility. The metric is very stable and also has the

Isotonicity is a very crucial requirement of a routing isotonicity characteristic. As a result, least weight pathsmetric for the efficiency of routing protocol. can be discovered proficiently. The weakness of this

Besides these characteristics, it is essential for a metric is that it does not address interference, channelmetric to find routes with the maximum throughput diversity, varying load of the link and capacity of the load.constantly. They should have a low packet delivery ratio These are the factors that are experienced by the links.during the transmission of the packet. It treats all the links identical. It finds path having poor

The next section will discuss the current routing throughput and high packet loss ratio. This is because themetrics deployed by WMN routing protocol for their links which are slower, take a lot of time to transmitstrengths and drawbacks. packets.

protocols are analyzed and a comparison of their

p

q

p

q

r

11(1 )1

1

k kETX kp pp

k

∞−= − =

−=∑

1*

ETXM Mf r

=

* SETT ETXB

=

World Appl. Sci. J., 30 (7): 870-886, 2014

880

W(p) W(q) W(r p) W(r q)Fig. 13: Isotonicity

Expected Transmission Count (ETX) Metric: The ETX computation of loop free routes and least weight as it ismetric [60] was presented to address the problems faced isotonic. The weakness of this metric is that it is not agileby Hop-Count metric. The ETX is the number of and is meant for single channel only. It does not considertransmissions required to successfully deliver a packet links interference and only captures a link loss ratioover a wireless link at the MAC layer. The ETX of a path thereby compromising link quality affects the link datais the summation of ETX of every link over the path. In rate transmission. It does not calculate traffic loss ratemathematical terms, it can be written: precisely as it doesn’t capture variation in rates of

P= 1-(1-P ) (1-P ) (5.1) network, because it does not consider varying link loadf r

where, minimize intra-flow interference as it is not able toP = Probability of unsuccessful transmission of packet differentiate among diverse channel routes and same

in a link from node a to node b. channel routes.P = Probability of path loss in forward direction.f

P = Probability of path loss in reverse direction. Expected Transmission Time (ETT) Metric: ETT metricr

The expected number of transmissions to account the bandwidth of different links. ETT is the timesuccessfully deliver a packet in one hop can be taken to communicate a packet successfully to the MACrepresented by. layer.

(5.2) (5.4)

The ETX metric for a single link is measured in terms S = Packet size (average) and of forward and reverse delivery ratio. B = Bandwidth of the current link.

(5.3) ETT metric is got by summation of all the ETT values

where, The advantage of ETT is, that it is isotonic andM = Forward delivery ratio is (1-P ) increases the performance of the whole network byf f

M = Reverse delivery ratio is (1-P ) increasing the path throughput by determining linkr r

ETX measures the packet loss rate. Every one is unable to avoid the routing through the nodes and linkssecond, probe packets are sent to all neighboring nodes. which are severely loaded. It does not reduce inter- flowOn getting the probe packet, the neighboring node sums and intra-flow interference as it has not been designed forthe number of packets received. Based on this multi radio networks. information, every ten seconds packet loss rate iscomputed. It finds paths, which have a high throughput Weighted Cumulative Expected Transmission Timewith the minimum hops because a long path will have less (WCETT) Metric: WCETT [61] was presented toenhancethroughput because of intra-flow interference. It indirectly the ETT metric in the multi radio mesh networks by takinghandles inter-flow interference. It allows proficient into account the diversity of the channels.

transmission. It leads to an unbalanced load of the

and routes through heavily loaded nodes. ETX doesn’t

[61] was an enhancement over ETX as it took into

where,

of the different links on the path.

capability. It contains all the same drawbacks of ETX. ETT

(1 ) * *WCETT ETT MaxXp j= − +∑

1n

X ETT j kj ihops on channel j

= ≤ ≤∑

1( )* min( )

MIC p IRU CSCL iN ETTi p i p

= +

∈ ∈∑ ∑

* SETT ETXjk jk B jk=

B jB jkjk

=

1

NRC B gj j jl jl

k

= −

=∑

World Appl. Sci. J., 30 (7): 870-886, 2014

881

The WCETT metric of a path p is defined as follows: (5.7)

(5.5)

where, ETT value X = Summation of links ETT values which are on It consists of components of MIC, IRU (Interferencej

channel j in a system having orthogonal channels. Aware Resource Usage) and CSC (Channel Switching

(5.6)

is a tunable parameter between 0 1 which controls CSC = w2 if Ch Ch , 0 w1 < w2the preferences over the path length versus channeldiversity. N is the group of neighbors’ nodes, which interferes

WCETT is a weighted average of two components. with communications on link I. CH denotes channelThe first term is usually the summation of the individual allocated for i node communication and i-1 denotes thelink ETTs while the second term is the summation of the earlier hop of i node on the path p.ETTs of every link of a given channel. This adds channel MIC addresses both types of interference. Breakingdiversity to the routing metric causing low intra-flow into imaginary nodes through a least weight algorithminterference. Using WCETT, multi radio wireless mesh like Dijkstra's algorithm [64], it can be made isotonic.network's performance is enhanced in comparison to ETX, This metric is based upon the assumption that whateverETT and Hop-Count metrics. WCETT metric is not links are positioned in the interference region for aisotonic and due to this, it can’t be used with link state specific link adds an equal amount of interference. Itrouting protocols. Secondly, the inter-flow interference calculates total interference on a particular link througheffects are not explicitly taken into account by WCETT. the placement of interference creating nodes irrespectiveAs a result of this, sometimes paths are created, which of participating in transmission concurrently or not.have high levels of interference. WCETT is very effective Intra-flow interference is captured in two successive linksin selecting paths having channel diversity as it takes only by the CSC which is the second component.intra-flow interference into consideration. It retains thegains of ETT metric barring isotonicity.Multi-radio Load Aware Expected Transmission Time (LAETTwireless mesh network performance is enhanced after Metric): There are two main aims of LAETT [65]. The aimusing WCETT in comparison to Hop-Count, ETX and is to create a path for fulfilling the flow bandwidth demandETT metrics. It maintains a balance between delay and and to keep a space for the future needs. It is athroughput. combination of load estimation and features of wireless

WCETT does not consider the locality information of access. It comprises of an implementation of ETT metric.the links instead, it considers those links which areoperational on that channel. It assumes that there is an (5.8)interference by the links which are operational on thesame channel which may lead to congested paths. It is notisotonic as it can be seen by the presence of the second ETX = Expected transmission count on the link (j, k)term. As it does not have isotonicity, it is not easy to use S = Size of the packetfor link state routing protocols. This metric has the same B = Bit rate limitations as ETT/ETX metric as it does not estimateactual link presence. Also it does not take into accountinter-flow interference effect. As a result, routes with highinterference may be established.

Metric of Interference and Channel Switching (MIC):MIC metric [62-63] is an isotonic metric and designed toconsider inter and intra-flow interference effects besidesproviding load balancing. For a path p

N = Total nodes and min (ETT) = Network’s least

Cost).

IRU = ETT * N .L L L

CSC = w1 if Ch = CHi i–1 i

i i–1 i

L

ith

th

jk

jk

Where B is the j node communication ratejth

= Link Quality Factorjk

= 1 for a very good linkjk

Remaining capacity (RC ) for every node is. i

*

2

SLAETT ETXjk jk RC RCj kjk

=+

( )i

EETT ETTk ilink IS k

=

∈∑

( )( ) , ( ) ( ) ( )

( )

IL QjkAIL Q N Q N Q N Qjk L j kN QNL L= = ∪∑

1 min( ) * min( ), ( ) 0

1 min( ), ( ) 0

ETT AIL N Ql

ETT N Ql

= ≠

= =

( ) (1 ) * * max11

niAware p iAWARE Xi k l k

i

= − + ≤ ≤=∑

ETTkiAWAREk IRk=

World Appl. Sci. J., 30 (7): 870-886, 2014

882

f is the rate of transmission of current flow Nj that travels MTI metric can be defined by the following equation.jl

across j node. The flow cost on the leftover bandwidthth

is weighted by factor . A superior communication MTI (Q) = ETT (Q) * AIL (Q), N (Q) 0jl

results in a lower usage of bandwidth in comparison to MTI (Q) = ETT (Q), N (Q) = 0inferior communication.

LAETT is defined by: when communicating amongst nodes j and kjk

(5.9)

The equation 5.9 consists of two parts. The later partcaptures the leftover bandwidth present on either sides of Il (Q) = Neighbors interfering loadthe node. If there are two paths having identical aggregate N (Q) = Interfering nodes set of neighbors j and k.ETX weight, LAETT gives importance to the path havingthe greatest leftover bandwidth. LAETT advantage is that “Scaling factor is applied to MTI metric forit is isotonic and load aware. It utilizes shortest weighted balancing the difference in magnitude of two componentsrouting path for balancing the network load. It also (MTI and CSC). can be represented as:captures traffic load and quality of links. The weakness ofthis metric is that it does not consider intra-flowinterference and is not considered as it does not considerinter-flow interference.

Exclusive Expected Transmission Time (EETT): EETT Min (AIL) ”= load average and [66] is an innovative routing metric which is interference Min (ETT) = least ETT aware. It finds multichannel routes having minimuminterference to have a high throughput. Multi-channel The estimation of interfering nodes' load is a keypaths are given better valuation by it. The k link EETT is issue in the deployment. th

given by the following equation: ILA takes into account disadvantages of prevailing

(5.10) successfully discovers lower congested and a low level

The path’s weight is the addition of EETTs of packet loss ratio. Inter-flow interference is calculated bycomplete links falling on that route. EEET has all the ILA. The drawback of this metric is that in two successivebenefits of ETT as it has been built over ETT. It is also links only, the second component CSC can captureisotonic. It efficiently takes into account intra-flow intra-flow interference.interference directly and considers inter-flow interferenceindirectly. The drawback of this is that it does not Interference Aware Routing Metric (iAWARE):consider load variation. iAWARE metric [68] can be said as the first metric which

Interference Load Aware (ILA): ILAmetric [67] consists WMN. The iAWARE metric can be illustrated as.of two components: Channel Switching Cost (CSC) andMetric of channel interference (MTI). (5.11)

CSC component can be defined by the followingequation.

CSC = w1 if Ch = Ch value is. j j–1 j

CSCj = w2 if Ch Ch , 0 w1 < w2j–1 j

CH (j) represents channel assigned for node thetransmission and j-1 represents the previous hop of the Ir =Interference ratio among two nodes a and b for anode j along path p. link k.

j jk jk l

j ij l

AIL = Neighbors average load which may interferejk

using channel Q.

jk

L

metrics like WCETT, ETX, ETT and Hop-Count. It

interference path which has high throughput and a low

considers both inter-flow and intra-flow interference in

X is identical to WCETT. For a link k,the iAWAREk

k

min( ( ), ( )( )

( )( )

IR IR a IR bk k kSINR alIR aj SNR al

=

=

World Appl. Sci. J., 30 (7): 870-886, 2014

883

Table 1: Comparison of the existing metrics.

Routing Metrics Inter Intra Link Loss Ratio Over Heads Load Balancing Multi Channel Isoto Nocity Link Data Rate Multi /Single Radio

HOP NO NO NO NO NO NO YES NO SINGLEETX NO NO YES NO NO NO YES NO SINGLEETT NO NO YES NO NO NO YES YES SINGLEWCETT NO YES YES NO NO YES NO YES MULTIMIC YES NO YES YES NO YES YES YES MULTIILA YES YES YES YES NO YES NO YES MULTIiAWARE YES YES YES NO NO YES NO YES MULTIEETT YES YES YES NO NO YES YES YES MULTILAETT NO NO YES NO YES NO YES YES MULTI

CONCLUSION

SNR (a) = for link l node a’s signal to noise ratio protocols and routing metrics proposed for wireless meshi

iAWARE can capture varying transmission rates, the basis of geographical, hierarchical and multi-pathintra and inter-flow interference and varying link loss ratio routing butin this survey only the broadly classifiedeffects. This metric preserves all the features of WCETT routing protocols for wireless mesh networks havebarring the mechanism of countering inter-flow been considered. Also an attempt to present ainterference calculation. Average interference produced comprehensive review of popular routing metrics hasfrom neighboring nodes is directly measured. SINR been done.implementation is a big step forward for minimizinginter-flow interference routing in comparison with metrics ACKNOWLEDGEMENTETX and WCETT. The weakness of iAware is that it doesnot possess isotonicity. If a link has higher IR in The researcher wish to thank the Deanship ofj

comparison to ETT , iAWARE value is lower as a result a Scientific Research, College of Engineering, King Saudj

lower ETT path but having greater interference is chosen. University for supporting this research.The biggest weakness of iAWARE is that it allocatesadditional weightage to ETT in comparison to interfering REFERENCESlinks.

Besides the routing metrics which have been 1. Akyildiz, I.F., X. Wang and W. Wang, 2005. Wirelessdiscussed, other researchers proposed adaptive load mesh networks: a survey. Journal of Computeraware routing metric (ALARM) [69] and a location aware Networks Journal, 47(4): 445-487.routing metric (ALARM) [70] considering inter and 2. Bruno, R., M. Conti and E. Gregori, 2005. Meshintra-flow interferences and load balancing on top of networks: commodity multi-hop ad hoc networks,being isotonic. A round trip time metric (RTT) was IEEE Communications Magazine, 43(3): 123-131.presented which was load dependent but resulted in 3. Chlamtac, I., M. Conti and J. Fr, 2003. Mobile ad hocunstable routes [71]. Medium Time Metric (MTM) [72] networking: imperatives and challenges. Ad Hocconsiders the overhead in Media Access Control (MAC) Networks Journal, Elsevier, 1(1): 13-64.layer. An Adjusted Expected Transfer Delay (AETD) 4. Siraj, M. and K.A. Bakar, 2011. Link establishmentmetric was proposed, which considers delay and jitter of and performance evaluation in IEEE 802.16 wirelesspaths to make a decision, but it falters when there is high mesh networks. Int. J. Phys., 6(13): 3189-3197.interference in the channels [73]. Some other routing 5. Fong, B., N. Ansari, A.C.M. Fong, G.Y. Hong andmetrics presented are Interference-Aware Routing Metric P.B. Rapajic, 2004. On the scalability of fixed(IAR) [74],Success Probability Product (SPP) [75], broadband wireless access network deployment.Expected Multicast Transmissions (EMT) [76] and Link Proceedings of IEEE Radio Communications,Aware Metrics [77-78]. 42(9): S12-S18.

The strengths and weakness of the metrics discussed 6. Held, G., 2005. Wireless mesh networks. Auerbachare summarized in Table 1. Publications, Taylor & Francis Group.

This paper presents a survey of the routing

networks. Routing algorithms can also be categorized on

World Appl. Sci. J., 30 (7): 870-886, 2014

884

7. Gupta, P. and P.R. Kumar, 2000. The capacity of 19. Chen, Y., G. Zhu, et al., 2008. On the Capacity andwireless networks. IEEE Transactions on Information Scalability of Wireless Mesh Networks, WirelessTheory, 46(2): 388-404. Communications, Networking and Mobile

8. Jovic, A., P. Vishwanath and S. Kulkarni, 2004. Computing, pp: 1-5.Upper bounds to transport capacity of wireless 20. Yonghui Chen, 2011. On the Capacity and Scalabilitynetworks. Proceedings of IEEE Transactions of of Wireless Mesh Networks, Wireless MeshInformation Theory, 50(11): 2555-2565. Networks, In Tech, Available from:

9. Jun, J. and M. Sichitiu, 2003. The nominal capacity of http://www.intechopen.com/books/ wireless-mesh-wireless mesh networks. IEEE Wireless networks/on-the-capacity-and-scalability-of-wireless-Communications Magazine, 10(5): 8-14. meshnetworks

10. Li, J., C. Blake, D.S.J. Couto, H.I. Lee and R. Morris, 21. Pourfakhar, E. and A.M. Rahmani, 2010. A hybrid2001. Capacity of ad hoc wireless networks. In QoS multicast framework-based protocol for wirelessProceedings of 7 ACM International Conference on mesh networks, Computer Communications,th

Mobile Computing and Networking. 33(17): 2079-2092.11. Lam, R.K., D.M. Chiu and J.C.S. Lui, 2007. On the 22. Xue, Q. and A. Ganz, 2002. QoS Routing for

access pricing and network scaling issues of wireless Mesh-Based Wireless LANs, International Journal ofmesh networks. IEEE Transactions on Computers, Wireless Information Networks, 9(3): 179-190.56(11): 1456-1469. 23. Aoun, B., R. Boutaba, Y. Iraqi and G. Kenward, 2006.

12. Leveque, O. and E. Telatar, 2005. Information Gateway Placement Optimization in Wirelesstheoretic upper bounds on the capacity of ad hoc Mesh Networks with QoS Constraints, IEEEnetworks. Proceedings of IEEE Transactions of Journal of Selected Areas in Communications,Information Theory, 51(3): 858-865. 24(11): 2127-2136.

13. Jelenkovic, P.R., P. Momcilovic and M.S. Squillante, 24. Drabu, Y. and H. Peyravi, 2008. Gateway Placement2007. Scalability of wireless networks. Proceedings with QoS Constraints in Wireless Mesh Networks inof IEEE/ACM Transactions on Networking, Proc. of Seventh International Conference on15(2): 295-308. Networking, pp: 46-51.

14. Huang, L.F. and T.H. Lai, 2002. On the scalability of 25. Junhai, L., Y. Danxia, X. Liu and F. Mingyu, 2009. AIEEE 802.11 ad hoc networks. Proceedings of the Survey of Multicast Routing Protocols for MobileThird ACM International Symposium on Mobile Ad Ad-Hoc Networks, IEEE Communications SurveysHoc Networking and Computing (MobiHoc’02), and Tutorials, 11(1): 78-91.173-182. 26. Sun, B. and L. Li, 2006. QoS-aware multicast routing

15. Peraki, C. and S.D. Servetto, 2003. On the maximum protocol for Ad hoc networks, Systems Engineeringstable throughput problem in random networks with and Electronics, 17(2): 417-422.directional antennas. Proceedings of the 4th ACM 27. Tang, J., G. Xue and W. Zhang, 2005. Interference-international symposium on Mobile Ad Hoc aware topology control and QoS routing in multi-Networking & Computing, pp: 76-87. channel wireless mesh networks, MobiHoc.

16. Yi, S., Y. Pei and S. Kalyanaraman, 2003. On the 28. Yong, D., K. Pongaliur and X. Li, 2009. Hybridcapacity improvement of ad hoc wireless networks multi-channel multi-radio wireless mesh networks,using directional antennas. Proceedings of the 4 IWQoS. 17 International Workshop.th

ACM international symposium on Mobile Ad Hoc 29. Perkins, C. and Bhagwat, 1994. Highly DynamicNetworking & Computing, pp: 108-116. Destination-Sequence Distance Vector, Routing

17. Jiang, W., Z. Zhang and X. Zhong, 2007. (DSDV) for Mobile Computers,” in Proc. of ACMHigh throughput routing in large-scale multi-radio SIGCOMM Computer Communication Review,wireless mesh networks. Proceedings of the ECNC, 234–244.pp: 3598- 3602. 30. Pei, G., M. Gerla and T. Chen, 2000. Fisheye state

18. Arpacioglu, O. and Z.L. Haas, 2004. On the scalability routing in mobile ad hoc networks. In Proceedings ofand capacity of wireless networks with the 2000 International ICDCS Workshop on Wirelessomnidirectional antennas. Proceedings of the Networks and Mobile Computing. 10-10 April. Taipei:IPSN’04, Berkeley, California, USA, pp: 169-171. Citeseer, D71-D78.

th

World Appl. Sci. J., 30 (7): 870-886, 2014

885

31. Jacquet, P., P. Muhlethaler, A. Qayyum, A. Laoutit, L. 42. Royer, E.M., 1999. A review of current routingViennot and T. Clausen, 2003. Optimized Link State protocols for ad-hoc mobile Wireless Networks,Routing Protocol (OLSR), IETF RFC 3626, 6(2): 46-55.http://www.olsr.net/,http://www.olsr.org/. J.J. Garcia 43. Park, V.D. and M.S. Corson, 2001. Temporally-and M. Spohn, 1999. “Source-tree routing in wireless Ordered Routing Algorithm (TORA) version 4:networks,” in ICNP, pp: 273-282. Functional specification". Internet-Draft, draft-

32. Baumann, R., S. Heimlicher, V. Lenders and M. May, ietfmanet-TORA-spec-04.txt, July 2001.2007. HEAT: Scalable routing in wireless mesh 44. Johnson, D. and D. Maltz, 1996. Dynamic Sourcenetworks using temperature fields, in IEEE Routing in Ad Hoc Networks. Mobile Computing, pp:International Symposium on World of Wireless, 152-81.Mobile and Multimedia Networks. 45. Toh, C.K., 1997. Associativity-based routing for ad

33. Murthy S. and J.J. Garcia-Luna-Aveces, 1996. An hoc mobile networks, Wireless PersonalEfficient Routing Protocol for Wireless Networks, Communications, 4(2): 103-139.ACM/Baltzer Journal on Mobile Networks and 46. Draves, R., J. Padhye and B. Zill, 2004. Routing inApplications, Special Issue on Routing in Mobile multi-radio, multi-hop wireless mesh networks. InCommunication Networks, 1(2): 183-197. Proc. of ACM MOBICOM.114-128.

34. Grace, K., 2000. Mobile Mesh Routing Protocol 47. Chakeres, I.D. and C.E. Perkins, 2010. Dynamic(MMRP), http://www.mitre.org/ work/tech_transfer/ MANET On-demand (DYMO) Routing.mobile mesh/. http://tools.ietf.org/html/draft-ietf-manet-dymo-21.

35. Gerla M. and J.T. Tsai, 1995. Multicluster, Mobile, 48. Corson M.S. and A. Ephremides, 1995. A DistributedMultimedia Radio Network, Proc. ACM Wireless Routing Algorithm for Mobile Wireless Networks,Networks, 1(3). ACM/Baltzer Wireless Networks, 1(1): 61-81.

36. Iwata, A., C.C. Chiang, G. Pie, M. Gerla and T. Chen, 49. Popa, L., A. Rostamizadeh, R.M. Karp, C.1999. Scalable Routing Strategies for Ad-Hoc Papadimitriou and I. Stoica, 2007. Balancing TrafficWireless Networks, IEEE Journal on Selected Areas Load in Wireless Networks with Curveball Routing,in Communications, Special Issue on Ad-Hoc Proc. Eighth ACM International.Networks, 17(8): 1369-1379. 50. Aguayo, D., J. Bicket and R. Morris, 2003. SrcRR: A

37. Bellur, B., R.G. Ogier and F.L. Templin, High-Throughput Routing Protocol for 802.11 Mesh(2004).Topology Dissemination Based on Reverse- Networks, http://pdos.csail.mit.edu/rtm/srcrr-Path Forwarding (TBRPF), IETF RFC 3684. draft.pdf.

38. Lee, Y.Z., M. Gerla, J. Chen, B. Zhou and A. Caruso, 51. Feng, J., R. Xia and H. Zhou, 2007. Interference-2006. Direction forwarding Routing, Proc. Ad-Hoc & Aware Load Balanced Routing in Wireless MeshSensor Wireless Networks, 2(2). Networks, Proc. International Conference Wireless

39. Bertsekas, D.P. and R.G. Gallager, 1987. Distributed Communications, Networking and Mobile ComputingAsynchronous Bellman-Ford Algorithm, Data (WiCom'07), pp: 1730-1734.Networks, Prentice Hall, Englewood Cliffs, 52. Santivanez, C. and R. Ramanathan, 2003. Hazypp: 325-333. sighted Link State (HSLS) Routing: A scalable Link

40. Jun, J. and M.L. Sichitiu, 200). MRP: Wireless mesh State Algorithm, BBN technical memo BBN-TM-1301,networks routing protocol. Computer BBN Technologies, Cambridge.Communications, 31(7): 1413-1435. 53. Hass, Z.J. and R. Pearlman, 1999. Zone routing

41. Hamma, S., E. Cizeron, H. Issaka and J.P. Guedon, protocol for ad-hoc networks,2006. Performance evaluation of reactive and http://tools.ietf.org/html/draft-ietf-manet-zone-zrp-04.proactive routing protocol in IEEE 802.11 ad hoc 54. Nikaein, N., C. Bonnet and N. Nikaein, 2001. HARP:network, Proc. SPIE 6387 Adhoc and Sensor Hybrid Ad-Hoc Routing Protocol, Proc. InternationalNetworks, Next-Generation Communication and Symposium on Telecommunications (IST'01).Sensor Networks, 638709. 55. Joa-Ng, M. and L.T. Lu, 1999. A peer-to-peer zone-

42. Liu, C. and S. Kaiser, 2005. A Survey of Mobile based two-level link state routing for mobile Ad-HocAd-Hoc network Routing Protocols, Tech. Report networks, IEEE Journal on Selected Areas inand (2003-08). Communications, 17(8): 1415-1425.

World Appl. Sci. J., 30 (7): 870-886, 2014

886

56. Hass, Z.J., R. Pearlman and P. Samar, 2002. The 70. Eiman, A. and S. Roy, 2008. A Location-AwareIntrazone Routing Protocol (IARP) for Ad-Hoc Routing Metric (ALARM) for Multi-Hop, Multi-Networks, Internet Draft, http://www.ietf.org/ Channel Wireless Mesh Networks, WCNCproceedings/ 02nov/I-D/draft ietf-manet-zone-iarp- Proceedings, pp: 2081-2086.02.txt. 71. Adya, A., P. Bahl, J. Padhye, A. Wolman and L.

57. Siraj, M. and K.A. Bakar, 2012b. A Load balancing Zhou, 2004. A multi-radio unification protocol forInterference Aware Routing Metric (LBIARM) for IEEE 802.11 wireless networks, Proceedings of themulti hop wireless Mesh Network Int. J. Phys. Sci., First International Conference on Broadband7(3): 456-461. Networks (BROADNETS’04), pp: 344-354.

58. Siraj, M. and K.A. Bakar, 2012. To minimize 72. Awerbuch, B., D. Holmer and H. Rubens, 2006. Theinterference in multi hop wireless mesh networks medium time metric: high throughput route selectionusing loadbalancing interference aware protocol, in multi-rate ad hoc wireless networks, Mob.World Applied Sciences Journal, 18(9): 1271-1278. Networking. Appl., 11(2): 253-266.

59. De Couto, D.S.J., D. Aguayo, J. Bicket and R. Morris, 73. Wei, Z., Z. Dongbo and D. Qiao, 2006. Comparative2003. A High-Throughput Path Metric for Multi-Hop study of routing metrics for multi-radio multi-channelWireless Routing,” in Proc. of the 9 annual wireless networks, in Wireless Communications andth

international conference on Mobile Computing and Networking Conference, 1: 270-275.Networking, pp: 134-146. 74. Waharte, S., B. Ishibashi, R. Boutaba and D.

60. Draves, R., J. Padhye and B. Zill, 2004. Routing in Meddour, 2008. Interference-aware routing metric formulti radio, multi hop wireless mesh networks. In improved load balancing in wireless mesh networks,proceedings of ACM MOBICOM.114-128. in Proc. of 2008 IEEE International Conference on

61. Yang, Y., J. Wang and R. Kravets, 2005. Designing Communications, pp: 2979-2983.routing metrics for mesh networks, Proc. WiMesh. 75. Roy, S., D. Koutsonikolas, S. Das and Y.C. Hu, 2006.

62. Yang, Y., J. Wang and R. Kravets, 2006. Interference- High-throughput multicast routing metrics in wirelessaware loop-free routing for mesh networks. mesh networks, in Proc. of 26 IEEE International

64. Dijkstra, E.W., 1959. A Note on Two Problems in Conference on Distributed Computing Systems,Connection with Graphs. Numerische Math., pp: 48.1: 269-271. 76. Zhao, X., C.T. Chou, J. Guo, S. Jha and A. Misra,

65. Aiache, H., V. Conan, L. Lebrun and S. Rousseau, 2008. Probabilistically reliable on demand multicast in2008. A load dependent metric for balancing Internet wireless mesh networks, in Proc. of IEEE WoWMoM,traffic in Wireless Mesh Networks," Mobile Ad Hoc 08: 1-9.and Sensor Systems, pp: 629-634. 77. Park, J.C. and S.K. Kasera, 2005. Expected Data Rate:

66. Jiang, W., S. Liu, Y. Zhu and Z. Zhang, 2007. An Accurate High-Throughput Path Metric forOptimizing Routing Metrics for Large-Scale Multi- Multi-Hop Wireless Routing, Proc. IEEERadio Mesh Networks” Wireless Communications, Communications Society Conference on Sensor andNetworking and Mobile Computing, pp: 1550-1553. Ad-Hoc Communications and Networks.

67. Shila, D.M. and T. Anjali, 2007. Load-aware Traffic 78. Kyasanur, P. and N.H. Vaidya, 2006. Routing andEngineering for Mesh Networks. Computer Link-layer Protocols for Multi-channel Multi-Communications and Networks, pp: 1040-1045. Interference Ad-Hoc Wireless Networks, Proc. ACM

68. Subramanian, A.P., H. Gupta, S.R. Das and J. Cao, Special Interest Group on Mobility of Systems,2008. Minimum Interference Channel Assignment in Users, Data and Computing (SIGMOBILE'06). MobileMulti-radio Wireless Mesh Networks, IEEE Computing and Communications, 10(1): 31-43.Transactions on Mobile Computing, 7(12): 1459-1473.

69. Pirzada, A.A., R. Wishart, M. Portmann and J.Indulska, 2009. ALARM: An Adaptive Load-AwareRouting Metric for Hybrid Wireless Mesh Networks,Proceedings of 32 Australasian Computer Sciencend

Conference, pp: 25-34.

th