Mobi-Herald: Alert Propagation for MANETs* Wenbo He, Ying Huang, Klara Nahrstedt, Whay C. Lee (Motorola) wenbohe@uiuc.edu, huang23@uiuc.edu, klara@cs.uiuc.edu, Whay.Lee@motorola.com Illinois Center for Wireless Systems Problem: How to trigger the defense against malicious attacks in the mobile ad hoc network after malicious behavior is detected locally?  Mobility Assisted Alert Propagation System Architecture: Design Goals: Efficiency (2) Reliability (3) Suppression of fake alert messages (4) Robustness (5) End-to-end delay of alert propagation Mobility-assisted epidemic routing: A mobile node retransmits a message periodically - An example (1) t=t0 (2) t=t0+T (3) t=t0+2T (4) t=t0+3T Quorum-based Verification: Resist malicious slander attacks. Assuming k is the number of collusive slanders, a node does not actively forward the received alert message before it received Q (Q>k) copies of the alert message. Alert propagation management: Balance reliability and efficiency A parameter “Times-to-send (TTS)” is attached in the message header, which indicates how many times an alert should be retransmitted by a mobile herald. Large TTS  large message overhead Small TTS  Small coverage of message delivery Balance end-to-end delay of alert propagation and efficiency Period of alert propagation “T” Large T  large end-to-end delay Small TTS  less efficiency of retransmissions Simulation Results: We simulate Mobi-herald alert propagation protocol under Random Waypoint mobility pattern. (1) Message overhead: (2) Coverage of message delivery (3) The protocol can successfully suppress fake alert messages generated by slanderers, if the number of collusive slanders is less than k. (4) Mobi-herald protocol achieves reasonable end-to-end alert propagation delay. * This work is supported by Motorola, and a patent is filled by Motorola