摘要:Any node can receive a lot of information about the network by placing its interface into promiscuous mode. The information the node can receive can be used to build trust levels for different modes.
ckets. These weights have a discrete range from 1 to +10 representing the significance of a particular event from unimportant to most important. The trust values for all the events from a node can then be combined using individual weights to determine the aggregate trust level for another node. We denote this trust by T, and is given by the following equation:
T = [ Wx(i) x Tx(i) ]
Where Wi is the weight of the ith trust categoryand
Ti is the situational trustin the ith trust category.
5.3 Extension to OLSR:
In previous section our trust model is presented. This is a general model which can be extended to any protocol. But in our work we apply it to OLSR protocol.
5.3.1 OLSR Protocol
The Optimized link state routing Protocol (OLSR) protocol is a pro-active routing protocol. OLSR is an extension to LSR protocol. The most interesting feature about OLSR protocol is that each node has a set of Multi Point Relays (MPRs) and can only forward all its packets through MPRs.
5.3.2 Trust Derivation
In OLSR, we use the following two features to build up trust categories for our model:
1) Forwarded Packets (Acknowledgments)
A node can get information about the successful transmission of any packet that it sent, through the following two methods:
Link-Layer
Acknowledgements
Using Link-Layer acknowledgments the underlying MAC protocol provides feedback of the successful delivery of the transmitted data packets.
Network Layer
acknowledgements
This method permits the sender to explicitly request a network layer acknowledgement from the next hop.
All of the above methods provide information about the successful transmission of a packet.
The method acknowledgment is further classified into two categories.
Data packets acknowledgements
Control packets acknowledgements
The number of these acknowledgements occurring with respect to every node are maintained and tabulated as shown in Table. For every packet transmitted the appropriate counter in the table for success or failure is incremented, depending if the selected MPR node has correctly forwarded it or not.
2) Received Packets
The accuracy of received data and routing packets offers a measure to compute trust levels. For instance, if routing packets are received that are found to be correct and efficient, then the originator can be allotted a higher trust value along with the set of nodes provided in that packet. The above method can be further categorized into data and control packet types and allocated different trust values as shown in Table. Counters are maintained for every received packet that are incremented based upon the accuracy or inaccuracy of the packet.
5.3.3 Trust Quantification
The events recorded in the tables during the trust derivation process are quantized and assigned weights so as to compute the situational trust values for different nodes.
Trust Category Forwarded (Acknowledged) Packets
The trust category PA derived from the events recorded in Table 5-1 is based upon Packets acknowledged. The events are quantized as per the following equations to provide trust levels:
Dpa = (Dps – Dpf)
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