Wireless Pers Commun (2012) 62:201–214DOI 10.1007/s11277-010-0048-y

Cross Layer Secure and Resource-Aware On-DemandRouting Protocol for Hybrid Wireless Mesh Networks

Shafiullah Khan · Jonathan Loo

Published online: 9 June 2010© Springer Science+Business Media, LLC. 2010

Abstract Secure routing is one of the challenges offered by hybrid wireless mesh networks(WMNs). Researcher are implementing different approaches for mesh routing, but still needmore efforts in terms of security, efficiency, deployment and capability with different sce-narios and applications. Cross layer secure and resource-aware on demand routing (CSROR)protocol for hybrid WMN is designed to ensure routing security and fulfil different appli-cations specific requirements for multimedia delivery and real-time transmissions. CSRORselects an optimum route on the basis of route security taking in consideration the differentcross layer parameters. CSROR is not only resource aware approach but also resilient todifferent packet dropping attacks. It is evaluated in diverse range of hostile hybrid WMNscenarios.

Keywords Routing protocol · Cross layer · Wireless mesh networks · Resource aware ·Security

1 Introduction

Hybrid WMN is the combination of infrastructure less and infrastructure based [2] multi-hop wireless networks. Infrastructure less WMN is the form of mobile ad hoc networks(MANETs) having no fixed routers. Every node has mobility capability and the overallarchitecture is dynamic in nature with all the nodes have routing ability. Infrastructure based

S. Khan (B) · J. LooSchool of Engineering and Design, Brunel University, Uxbridge, UKe-mail: Shafiullah.khan@brunel.ac.uk

J. Looe-mail: Jonathan.loo@brunel.ac.uk

S. KhanKohat University of Science and Technology (KUST), Kohat, Pakistan

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WMN is similar to multi-hop WLAN having fixed routers or access points, and the nodescan be either static or mobile.

Many routing algorithms have been designed for ad hoc networks. Due to different char-acteristics and requirements of hybrid WMNs, such algorithms may not perform well andconsequently demands different routing strategies [28]. Existing routing protocols such asad-hoc on demand distance vector (AODV), dynamic source routing (DSR), link qualitysource routing (LQSR), optimized link state routing (OLSR) are proposed for homogeneousad hoc network, and cannot be adapted in heterogeneous WMN. Furthermore, most of exist-ing routing mechanisms for multi hop environments lack security consideration by assumingnon-hostile environment where nodes are cooperative and non-malicious [16].

Secure routing is the basic and critical aspects of any wireless network especially multihop heterogeneous wireless networks. The range of security threats increases in multi hopwireless networks as compared to single hop wireless networks due to decentralized archi-tecture and large scale mobile nodes with routing capability. Implementation of appropriatesecure routing protocol in hybrid WMN is a challenging task. Along with security, the routingprotocol must have the capability to handle the unpredicted dynamic topological changes andthe multi-hop data transfer in which the source-destination route may involve many inter-mediate access points and nodes. Such multi hop paths may have many security threats suchas packets dropping, selectively forwarding, altering and route modifications. Secure hybridWMN routing protocol is difficult to design due to the characteristics of both MANETs andmulti hop WLANs.

Cross layer secure and resource-aware on demand routing (CSROR) protocol is designedkeeping in view the limitations and requirements of hybrid WMN. CSROR is based oncross-layer information exchange scheme in which routing protocol makes use of differentparameters from different layers across the protocol suite for decision making at the net-work layer. In CSROR, the route selection is done at destination node on the basis of pathsecurity, bandwidth and battery life. The route request (RREQ) packet contains three fields,which are updated along the path. These three fields capture the values of total threat levelof the route, lowest bandwidth and battery life. CSROR always maintains an alternate routein case of path failure due to topological changes. The security mechanism of CSROR istaken from our previous published work [19]. CSROR is resilient to packet dropping attackssuch as blackhole grayhole [4,23] and packet misdirecting attacks such as wormhole attacks[10,15,29,30].

In this paper, we present a cross layer secure and resource-aware on demand routing(CSROR) protocol, which is based on cross layer parameters such as data rate, delay andsecurity considerations. CSROR is resilient to many multi hop security attacks such as packetdropping, selective forwarding, looping and misdirecting.

The rest of the paper is organized as follows. Section 2 discusses relevant related work.Overview of protocol design considerations and parameters are briefly covered in Sect. 3.Our cross layer secure routing protocol is discussed in detail in Sect. 4. Section 5 describesthe evaluation and simulation results. Section 6 concludes the paper.

2 Related Work

Research community is trying to test ad hoc routing in hybrid WMN environment, however,due to variation in characteristics, such efforts are not fruitful [25,28,27]. Some researchershave proposed specialized routing protocols for wireless mesh networks such as AODV-CGA [5], orthogonal rendezvous routing protocol (ORRP) [9], RingMesh [20], destination

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sequence distance vector (DSDV) routing protocol [24], ad-hoc on demand distance vectorspanning tree (AODV-ST) [25], hybrid on demand distance vector routing (HOVER) [22],optimal routing with varying traffic demand [11], resilient and opportunistic mesh routing(ROMER) [31], SrcRR [1] and HEAT [6]. All these existing routing protocols for mesh net-works are without security considerations and are based on assumption of non-hostile andnon-malicious mesh environment.

Multipath secure hybrid routing is presented in [26], in which the backup mechanism usesthe multipath. It uses both table driven and demand driven approaches with more routingoverheads. A secure intra-mesh routing protocol (SIMRP) [18] is resistant to fabrication,replay and most of the common security attacks, but it is unable to respond to collaborative,blackhole, grayhole and wormhole attacks. JANUS [8] is a framework for secure routing inWLANs and cellular networks, which are single-hop in nature, so this mechanism may notperform well in a multi-hop wireless networks.

Secure routing protocol for mesh (SRPM) is proposed [19] for infrastructure based WMN,although it ensure the security of packet transmission by calculating unreliability value ofroutes between source and destination, but it is not suited for hybrid WMN due to ad hocnature of nodes at lower end.

3 Protocol Design Considerations and Parameters for Hybrid WMN

The routing protocols for hybrid WMN must capable to handle variety of hosts and ensureintegration of different nodes with different resources such as bandwidth, data rates andenergy. Path selection of most of existing routing protocols such as link state protocols anddistance vector routing protocols, is based on either Bellman-ford algorithm [7] or Dijkstra’salgorithm [13].

The hybrid routing techniques combine the proactive and reactive path formation to over-come delay and control overhead [14,17]. Different routing protocols use different nodes fordecision and route selection such as source node, intermediate node or destination node. Thedecision and route selection is based on routing metrics such as hop count, link quality, datarate, node life or reliability [12,21].

Hybrid WMN have the following features that are necessary to be considered while sug-gesting or designing solutions for this type of networks.

• Hybrid WMN is the combination of multi hop WLAN consisting of backbone of accesspoints and decentralized MANET at lower end as given in Fig. 1.

• The multi hop backbone of WLAN have more bandwidth capacity as compared to decen-tralized MANET.

• Power limitation is not an issue in multi hop WLANs region, however in MANETs region,energy is a critical factor.

• Security is one of the concern in multi hop wireless networks especially hybrid WMN. Inhybrid WMN, multi hop access points can be accessed by end user nodes from anywhere.Similarly, MANET region is not secured from threats such as denial of service attacks.

• In multi hop WLANs region, the network topology is almost static, however in theMANET region, the topology is dynamic and the nodes change their position randomly.

• The size of routing table in WLANs region is not so vital; however, it is desirable to keepthe routing table small in MANETs nodes to avoid large link overheads [3].

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Fig. 1 Architecture of hybrid WMN

4 Proposed Routing Protocol

This section provides detail of the proposed CSROR routing protocol in terms of routediscovery, maintenance, packets format, cross layer exchange of parameters and securityprovision.

4.1 Packets Format

CSROR uses two types of control packets for route discovery process i.e. a broadcast routerequest (RREQ) packet from source to destination, and a unicast route reply (RREP) packetfrom destination to source in reverse direction.

The RREQ packet consists of fields such as source ID, intermediate ID, destination ID,cross layer parameters and threat level (TL) of the route as shown in Fig. 2.

The source node broadcast the RREQ, and certain fields of the packets are updated at everyintermediate node till it reaches the destination. The source node fills some fields such as thesource ID and destination ID. When an intermediate node receives RREQ packet, it insert its

Fig. 2 Route request (RREQ) packet

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ID. It selects the lowest value of bandwidth and node battery along the route. Route TL valueis sum of drop values (DV) of entire route from source to destination. Every node calculatesthe DV value of all the one hop away neighbours. Security mechanism and computation ofTL value is discussed in more details in Sect. 4.2.

The destination node unicast the RREP packet consists of fields such as source ID, inter-mediate IDs and destination ID. The route selection decision is done by the destination nodeafter receiving one or many RREQ on the basis of the information such as node battery,bandwidth and TL value.

4.2 Route Parameters

CSROR relies on three different parameters for determining a shortest optimum route basedon available bandwidth, node battery power and threat level (TL).

To determine the available bandwidth, cross layer information exchange is used betweennetwork and MAC layers. In simulation software, the bandwidth or data rate is usually imple-mented at the MAC layer. The computed value of available bandwidth is passed to the CSRORprotocol via a cross layer interface.

In mobile nodes, battery power is an important metric for selection of an appropriate route.A random function is used to get random values of available power. We assign weights tointerpret the battery powers as shown in Table 1.

Another important parameter is the computation of TL of entire route in CSROR. TL canbe computed by adding the drop value (DV) of all the nodes in the route as below:

TL = DVn1 + DVn2 + DVn3 + DVn

where n1, n2, and so on are the intermediate nodes between source and destination. DV isthe computation of next hop dropping behavior. In CSROR, all nodes keep drop values forone hop neighbors. Higher drop values mean the node is more selfish and unreliable. TheDV is computed on the basis of a passive acknowledgement mechanism adopted from ourprevious work [19], and shown in Fig. 3.

Source S sends packets to n1, but receives passive acknowledgement from n2 to validatethe reliability of n1. Similarly, n1 forwards packets to n2, but receive passive acknowledge-ment from n3. The reason of this arrangement is to ensure the path reliability. In this scheme,n1 calculates DV of n2 as:

DVn2 = No. of packets forward to n2 − No. of Passive acknowledgements from n3

Table 1 Node battery power

Battery power More than 70% 50–70% 30–50% Less than 30%

Weight 1 2 3 4

Fig. 3 Packet transmission and two hop passive acknowledgement mechanism

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The more DV, the less secure is the node. Similarly, node n2 calculates DV of n3 and so on.The TL value field in RREQ packet is incremented along the path, if the next node has DV.

The two hop passive acknowledgement mechanism is resilient to blackhole, grayhole andwormhole attacks. In a blackhole attack, the compromised node presents itself as the shortestroute to the target node so it can drop the entire traffic flow passing through it. In a greyholeattack, a malicious node selectively forwards the packets toward the destination. In a worm-hole attack, the adversary captures the packet at one end and then forwards through a wormlink to another distant malicious node in order to create serious routing disruption [19].

In CSROR, if node n3 is compromised and acts like a greyhole by selectively forwardingpackets (drops some packets), the node n2 is constantly calculating the DV of node n3. Insuch a case, node n2 will not receive some passive acknowledgement (of lost packets) fromnode n4, which shows that the intermediate node n3 is compromised and it is acting as greyhole. In case, no passive acknowledgement is received, then node 3 is black hole.

4.3 Crosse Layer Information Exchange

The exchange of cross layer information is to use many parameters from different layersfor overall optimization of protocols across the communication stack and can be used totune various aspects of the wireless communication such as enforcing QoS support, powersaving, efficient scheduling, better application performance and better utilisation of networkresources.

The CSROR protocol uses information from both the MAC layer and application layer.Such an interaction is only possible with a cross layer information exchange. In CSROR,application layer conveys the reading of remaining battery life and MAC layer informs itabout the available bandwidth. The selected route of CSROR routing protocol is based onbandwidth, more battery life and less TL.

4.4 Route Discovery Process

CSROR uses the on-demand principle of route discovery as the routes are discovered onlywhen they are needed. The destination node selects the optimal route after receiving RREQpacket(s). The source node broadcasts RREQ packet to search available paths to destination.The fields in RREQ packets are updated at each intermediate node. The bandwidth and nodebattery fields capture the lowest reading along the path, while the route TL field is incre-mented to find the total drop value of the route. The destination node unicasts RREP afterevaluating the optimal path as given in Fig. 4.

In Fig. 4, the available routes from source to destination are as follow:

Route 1 {N1, N2, N3}Route 2 {N1, N4, N9, N3}Route 3 {N1, N4, N10}Route 4 {N5, N8, N10}Route 5 {N6, N7, N10}Route 6 {N6, N7, N11, N13}Route 7 {N6, N12, N13}

The destination node (DES) receives seven RREQ packets, in which the values of threeimportant fields (lowest bandwidth, low node battery and TL) are presented as:

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Fig. 4 Route discovery process of CSROR

RREQ of route 1: [2, 2.5, 115]

Where 2 represent the lowest node battery along the path, 2.5 represents the lowest avail-able bandwidth of the route, and 115 represents the total TL, which is the sum of DV alongthe route (which is 75+ 40).

Similarly, RREQ of route 2: [3, 2.5, 220]

RREQ of route 3: [2, 4, 200]RREQ of route 4: [4, 2, 230]RREQ of route 5: [3, 3, 190]RREQ of route 6: [3, 2.2, 217]RREQ of route 7: [3, 2.2, 132]

The destination node selects the most optimal route {N3, N2, N1} and unicasts RREP packetto source node.

In CSROR, route maintenance is done at destination node. Once the route is selected(as route 1 in Fig. 4), the destination node starts a timer to make sure the availability ofselected route. If the destination do not receive packets from source, and the timer expires,it is assumed that the route is broken, and the destination node selects another most optimalroute and again unicasts RREP to source node.

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5 Performance Evaluation

We conducted extensive simulations to analyze the performance of CSROR in both normaland malicious conditions, and compare it with SAODV (Secure ad hoc on demand dis-tance vector) and AODV routing protocols using NS-2. We used AODV-UU for SAODVsimulations.

The nodes used in the simulations were based on IEEE 802.11 with different data ratessuch as 1, 2, 5.5 and 11 mbps. The application traffic consists of constant bit rate (CBR)with a radio range of 100 m. The source and destination nodes were randomly selected. Thepacket size used is 512 bytes. The random waypoint mobility model is used. The differentparameters used are presented in Table 2.

Figure 5 shows the packet delivery ratio against maximum speed for CSROR, AODV andSAODV. AODV has low packet delivery ratio as compared to CSROR and SAODV, as bothCSROR and SAODV have multiple routes from source to destination and if any route isbroken due to mobility, they can still operates. The packet delivery percentage is more than85 in CSROR for all the node speeds. This shows effectiveness of CSROR in discoveringand maintaining routes in high mobility for delivering data packets.

Table 2 Simulation parameters Number of the nodes Random initial topology

Total simulation time 600 s

Packet size 512 bytes

MAC protocol IEEE 802.11b

Wireless node Data rate Variable 1, 2, 5.5, 11 mbps

Radio transmission range (m) 100

Mobility model Random waypoint

Area size 1,000 m×1,000 m

Maximum route request timeout 30 s

Protocols CSROR, SAODV, AODV

Fig. 5 Packet delivery ratio in mobility

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Fig. 6 End to end delay

Fig. 7 Routing overheads comparison

The average end to end delay for a network of 60 nodes in shown in Fig. 6. Small-est end-to-end delay is observed in case of CSROR. The end-to-end delay is increasedquickly with increasing node mobility in AODV due to lack of alternate path. When an activeroute is broken, AODV initiates route discovery procedure again. SAODV has slight moreend-to-end delay as compared to CSROR due to involvement of cryptographic operations inroute discovery.

The comparison of routing overhead for AODV, SAODV and CSROR is given in Fig. 7.CSROR has the lowest routing overheads due to the fact, that it can discover many alter-nate routes during route discovery process, which in turn reduced the rediscovery overheads.AODV has higher routing overheads due to frequent breakdown of active routes during highmobility, which triggered the route discovery process again.

The packet delivery ration in the presence of malicious node is shown in Fig. 8. Thesource node sends packets to destination, in which the malicious node is located near the

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Fig. 8 Packet delivery ratio in the presence of malicious node near the source

Fig. 9 End-to-end delay in the presence of malicious node near the source

source node. In AODV, the packet delivery is reduced to 15%, while in SAODV; the packetdelivery ratio is dropped to 60%. Here the packet delivery ratio of CSROR is above 85% inthe presence of malicious node near the source.

The end-to-end delay in the presence of malicious node near the source node is shownin Fig. 9. In AODV, the end-to-end delay is gradually increasing. However, the end-to-enddelay remains the same in case of SAODV and CSROR as in Fig. 6.

The packet delivery ratio of CSROR, SAODV and AODV with varying pause time in thepresence of malicious nodes is given in Fig. 10. In the presence of 25% malicious nodes ina network, the packet delivery ratio of CSROR is more than 85%. It is due to the fact thatCSROR is capable to calculate the TL of entire route, and the destination node selects themost optimal route of data transmission. The performance of AODV significantly decreasesgradually and reduces to 10% delivery rate.

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Fig. 10 Packet delivery ratio with varying pause time (25% malicious nodes)

Fig. 11 Average end-to-end delay with varying pause time (25% malicious nodes)

The average end-to-end delay of CSROR, SAODV and AODV with varying pause time inthe presence of 25% malicious nodes in a network is given in Fig. 11. CSROR has relativelyless end-to-end delay as compared to SAODV.

6 Conclusions

In this paper, various aspects of the CSROR protocol are presented in detail such as the routediscovery process, route maintenance, packets format for route request (RREQ), route replypacket (RREP) and route security mechanism used within route discovery. CSROR is basedon a cross-layer information exchange with security considerations. Comparison of CSRORwith two different well known routing protocols such as AODV and SAODV is done usingns-2. The comparison covers most of the scenarios such as the packet delivery ratio, average

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Table 3 Compariso 2n of CSROR, AODV and SAODV

CSROR AODV SAODV

On-demand route selection Yes Yes Yes

Alternative route Yes No Yes

Network size Small/medium/ large Large Medium/small

Routing path Adaptive Fixed Fixed

Link reliability Yes No Yes

Network load Low High Medium

Routing overhead Low High Medium

Application required adaptively Yes No No

delay and routing overheads with and without malicious nodes. The performance of the pro-tocol is analyzed according to varying pause time and velocities. CSROR is very effectiveagainst packet dropping attacks such as blackhole, grey hole and wormhole. Our future workintends to be in the direction of analyzing the protocol in a very large network with very highmobility in nodes and adapting this protocol for hybrid wireless mesh networks susceptibleto packet modification attacks.

References

1. Aguayo, D., Bicket, J., & Morris, R. (2004). ScrRR: A high throughput routing protocol for 802.11mesh networks.

2. Akyildiz, I. F., & Wang, X. (2005). A survey on wireless mesh networks. IEEE Commun Mag, 43(9),23–30.

3. Ali Ahmed, T. H. (2005). Modeling and simulation of routing protocol for ad hoc networks combingqueuing network analysis and ANT colony algorithms. PhD Thesis, University of Duisburg Essen,April.

4. Andel, T. R., & Yasinsac, A. (2007). Surveying security analysis techniques in MANET routingprotocols. IEEE Communications Surveys & Tutorial, 9(4),70–84.

5. Baumann, R., Heimlicher, S., Lenders, V., & May, M. (2007). Routing packets into wireless meshnetworks. In Third IEEE International Conference on Wireless and Mobile Computing, Networkingand Communications. (WiMOB).

6. Baumann, R., Heimlicher, S., Lenders, V., & May, M. (2007). HEAT: Scalable routing in wirelessmesh networks using temperature fields. In IEEE International Symposium on a World of Wireless,Mobile and Multimedia Networks (WoWMoM).

7. Bellman, R. (1958). On a routing problem. Quarterly of Applied Mathematics, 16(1), 87–90.8. Carbunar, B., Ioannidis, I., & Nita-Rotaru, C. (2008). JANUS: A framework for scalable and secure

routing in hybrid wireless networks. IEEE Transactions on Dependable and Secure Computing.doi:10.1109/TDSC.2008.14.

9. Cheng, B.-N., Yuksel, M., & Kalyanaraman, S. (2006). Orthogonal rendezvous routing protocol forwireless mesh networks. In Proceedings of the 14th IEEE International Conference on NetworkProtocols (ICNP).

10. Choi, S., Kim, D., Lee, D., & Jung J. (2008). WAP: Wormhole attack prevention algorithm in mobileAd hoc networks. In IEEE International Conference on Sensor Networks, Ubiquitous, and TrustworthyComputing.

11. Dai, L., Xue, Y., Chang, B., Cao, Y., & Cui, Y. (2008). Optimal routing for wireless mesh networkswith dynamic traffic demand. Mobile Networks and Applications, 13(1–2), 97–116.

12. De Couto, D. S. J., et al. (2003). A high-throughput path metric for multi-hop wireless routing. InProceedings of 9th ACM International Conference on Mobile Computing and Networking (Mobi-Com’03). San Diego, CA, Sept.

123

Hybrid Wireless Mesh Networks 213

13. Dijkstra, E. W. (1959). A note on two problems in connexion with graphs. Numerische Mathematik ,1,269–271.

14. Haas, Z. J. (1997). The routing algorithm for the reconfigurable wireless networks. In Proceedingsof 6th International Conference on Universal Personal Communications ICUPC, 2, 562–566, Oct.

15. Hu, Y.-C., Perrig, A., & Johnson, D. B. (2003). Packet leashes: A defence against Wormhole attacksin wireless networks. In 22nd Annual Joint Conference of the IEEE Computer and CommunicationsSocieties (INFOCOM).

16. Iiyas, M. (2002). The handbook of Ad hoc wireless networks. Boca Raton: CRC Press LLC, ISBN0-84931332-5.

17. Joa-Ng, M., & Lu, I. T. (1999). A peer-to-peer zone-based two-level link state routing for mobile Adhoc Networks. IEEE Journal on Selected Areas in Communications, 17(8), 1415–1425.

18. Kandikattu, R., & Jacob, L. (2007). A secure intra-domain routing protocol for wireless meshnetworks. Springer LNCS, 4812, 37–50.

19. Khan, S., Loo, K. K., Mast, N., & Naeem, T. (2010). SRPM: Secure routing protocol for IEEE802.11 infrastructure based wireless mesh networks. Network and Systems Management, 18(2).doi:10.1007/s10922-009-9143-3, June (in press).

20. Lin, D., Moh, T.-S., & Moh, M. (2006). A delay-bounded multi-channel routing protocol for wirelessmesh networks using multiple token rings: extended summery. In Proceedings of 31st IEEE Conferenceon Local Computer Networks.

21. Manoj, B. S., Ananthapadmanabha, R., & Siva Ram Murthy, C., (2001). Link life based routingprotocol for Ad hoc wireless networks. In Proceedings of 10th IEEE Int’l. Conf. Comp. Commun.(IC3N 2001), Oct.

22. Mir, S., Pirzada, A. A., & Portmann, M. (2008). HOVER: Hybrid on-demand distance vector routingfor wireless mesh networks. In Proceedings of 31st Australasian Science Conference (ACSC).

23. Module 7, routing and congestion control, version 2 CSE IIT, Kharagpur. Available at http://nptel.iitm.ac.in. (Accessed Feb. 2009).

24. Perkins, C., & Bhagwat, P. (1994). Highly dynamic destination sequenced distance vector routing(DSDV) for mobile computers. In Proceedings of the ACM SIGCOMM.

25. Ramachandran, K. N., Buddhikot, M. M., Chandranmenon, G., Miller, S., B-Royer, E. M., & Almeroth,K. C. (2005). On the design and implementation of infrastructure mesh networks. In Proceedings ofthe IEEE Workshop on Wireless Mesh Networks (WiMesh).

26. Siddiqui, M. S., Amin, S. O., Kim, J. H., & Hong, C. S. (2007). MHRP: A secure multipath hybridrouting protocol for wireless mesh network. In IEEE Military Communication Conference (MILCOM)(pp. 1–7).

27. Tsai, J., & Moors, T. (2006). A review of multipath routing protocols: From wireless Ad Hoc tomesh networks. In Proceedings of ACoRN Early Career Researcher Workshop on Wireless MultihopNetworking, Jul. 17–18.

28. Waharte, S., Boutaba, R., Iraqi, Y., & Ishibashi, B. (2006). Routing protocols in wireless meshnetworks: Challenges and design considerations. Multimedia Tools and Applications, 31(3), 285–303.

29. Wang, Y., Attebury, G., Ramamurthy, B. (2006). A survey of security issues in wireless sensornetworks. IEEE Communications Surveys and Tutorials, 8(2), 2–23.

30. Xing, F., & Wang, W. (2006). Understanding dynamic denial of service attack in mobile Ad hocnetworks. In IEEE Military Communication Conference (MILCOM).

31. Yuan, Y., Yang, H., Wong, S. H. Y., Lu, S., & Arbaugh, W. (2005). ROMER: Resilient opportunisticmesh routing for wireless mesh networks. First IEEE Workshop on Wireless Mesh Networks (WiMesh).

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Author Biographies

Shafiullah Khan is currently a Ph.D. candidate in the School ofEngineering and Design, Brunel University, West London, UK. Heis also affiliated with the Institute of Information Technology, KohatUniversity of Science and Technology (KUST), N.W.F.P, Pakistan asa lecturer. His research mainly focuses on wireless broadband net-work architecture, security and privacy, security threats and mitigatingtechniques.

Jonathan Loo received his M.Sc. (Distinction) and Ph.D. at Univer-sity of Hertfordshire, UK in 1998 and 2003, respectively. Thereafter, hejoined the School of Engineering and Design, Brunel University, WestLondon, UK, as a lecturer in multimedia communications. Currently,he serves as a course director for M.Sc. Digital Signal Processing andheads a team of nine active Ph.D. candidates in the area of multi-media communications. His current research interests include visualmedia processing and transmission, digital/wireless signal processing,and wireless/broadband network architecture, protocols and securities.

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