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The lack of centralised infrastructure in ad hoc network makes it vulnerable to various attacks. MANET routing disrupts if participating node do not perform its intended function and start performing malicious activity. A specific attack called Wormmhole attack enables an attacker to record packets at one location in the network, tunnels them to another location, and retransmits them into the network. In this paper, we present a protocol for detecting wormhole attacks without use of any special harware such as directional antenna and precise synchronised clock and the protocol is also independent of physical medium of wireless network. After the route discovery, source node initiates wormhole detection process in the established path which counts hop difference between the neighbours of the one hop away nodes in the route. The destination node detects the wormhole if the hop difference between neighbours of the nodes exceeds the acceptable level. Our simulation results shows that the WHOP is quite excellent in detecting wormhole of large tunnel lengths I. INTRODUCTIONAn ad-hoc network is inherently a self-organized network system without any infrastructure. Typically, the nodes act as both host and router at the same time i.e each node participates in routing by forwarding data for other nodes and deciding which nodes forward data next based on the network connectivity Most previous ad hoc networks research has focused on problems such as routing and communication, assuming a trusted environment. However, many applications run in untrusted environments and require secure communication and routing such as military or police networks, emergency response operations like a flood, tornado, hurricane or earthquake. However, the open nature of the wireless communication channels, the lack of infrastructure, the fast deployment, and the environment where they may be deployed, make them vulnerable to a wide range of security attacks.A particularly severe security attack, called the wormhole attack, has been introduced in the context of ad hoc networks. During this attack, a malicious node captures packets from one location in the network and "tunnels" them to another malicious node at a distant point which replays them locally. The tunnel can be established in many ways e.g. in-band and out-of-band channel. This makes the tunneled packet arrive either sooner or with a lesser number of hops compared to the packets transmitted over normal multi hop routes. This creates the illusion that the two end points of the tunnel are very close to each other. However, it is used by malicious nodes to

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In this article, the effect of four-wave mixing (FWM) and amplified spontaneous emission (ASE) noise on WDM optical star networks has been investigated. Analysis for the evaluation of probability of error has been carried out (a) when only FWM is present and (b) when both FWM and ASE noise are present. Numerical results are presented in the graphical and tabular forms for the practical values of parameters.Finally, optimal location of the amplifier in the network has been identified as being before the star coupler preceding the receiver.

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SUMMARYSession Initiation Protocol (SIP) has a retransmission mechanism to maintain the reliability for its real time transmission. But these real time transmissions cause overload in the server and creates redundant messages. SIP does not offer sufficient mechanisms for handling overload situations. In this paper, we study the SIP system behavior by separating signaling traffic in two different classes (I nvites and Non-invites) and creating a cut-off priority queueing model. SIP retransmission mechanism with timeout is modeled as a queueing system with impatient customers. Using this model, the effect of unnecessary retransmissions is studied, and delay distribution and loss probability (P b_loss) are calculated. The proposed analytical model is verified with simulations that demonstrate that the inclusion of timeout gives better delay performance. Using P b_loss, an algorithm is developed to control the overload in hop-by-hop transaction as described in RFC 6357. The simulation results for the proposed model with overload control and the standard SIP as per RFC 3261 are compared. The results demonstrate that the server utilization factor of an overloaded server always remains less than one and hence avoids system collapse. Further, the redundant messages in the system are reduced by 30% as compared with the standard SIP network.

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