TARMAC: Traffic-Analysis Reslient MAC Protocol for Multi-Hop Wireless   Networks
  Traffic analysis in Multi-hop Wireless Networks can expose the structure of the network allowing attackers to focus their efforts on critical nodes. For example, jamming the only data sink in a sensor network can cripple the network. We propose a new communication protocol that is part of the MAC layer, but resides conceptually between the routing layer and MAC, that is resilient to traffic analysis. Each node broadcasts the data that it has to transmit according to a fixed transmission schedule that is independent of the traffic being generated, making the network immune to time correlation analysis. The transmission pattern is identical, with the exception of a possible time shift, at all nodes, removing spatial correlation of transmissions to network strucutre. Data for all neighbors resides in the same encrypted packet. Each neighbor then decides which subset of the data in a packet to forward onwards using a routing protocol whose details are orthogonal to the proposed scheme. We analyze the basic scheme, exploring the tradeoffs in terms of frequency of transmission and packet size. We also explore adaptive and time changing patterns and analyze their performance under a number of representative scenarios. 
Ke Liu, Adnan Majeed and Nael B. Abu-Ghazaleh