“Survivable Routing in Multi-hop Wireless Networks” by Dr. Srikanth Krishnamurthy

Today we listened to Dr. Krishnamurthy give a talk on “Survivable routing in multi-hop wireless networks.” Multi-hop wireless networks have more than one node along its path to send a packet wirelessly from one point to another. This is much more cost effective than running cable because it consists of cheap hardware, it is quickly and easily extendable, it is easily manageable and reliable, and it is built rapidly. Many test beds are in use currently at MIT, U of Utah, UCR, and Georgia Tech. There are also public deployments being run in such places as Singapore.
Even though there is much research and work done with wireless multi-hop networks there are still many issues remaining. The issues are routing quality, reliability and security.
Dr. Krishnamurthy talked about ETX(Expected transmission count) routing metric. This is used to measure the quality of a path between two nodes in a wireless packet network. Facts that need to be considered when looking at this are order matters and the security. This metric does not take into account switching link positions would equals different costs. And it also doesn’t account for a finite number of retransmissions where a packet is dropped changes costs. These all degrade the reliability and quality of the transmission. ETX was designed to improve transmission but it does not cover security.
Dr. Krishnamurthy introduced ETOP. This takes into account all the issues that ETX does not cover; node order, dropped packets and security. The estimated cost of n-hop path is expected to be the number of transmissions plus the retransmissions required to deliver a packet over that particular path. Performance results give a 65% improvement over ETX routing for paths that are separated by 3 or more hops. TCP behavior with ETOP gives higher reliability with ETOP allowing TCP to be more aggressive and ramp up its congestion window. TCP transmission time improves.
But there are security issues that need to be address with ETOP. Dr. Krishnamurthy addresses the issues of vulnerable attacks on the system paths. Some solutions would be when sending out probes that each carry a message. Then the reply to the probes would not only be the probe number but the message value. Another is to respond on only certain channels in the system. These solutions would throw off attackers who were trying to fake link quality metrics to attack routes.
All in all Dr. Krishnamurthy feels that ETOP is a better, more reliable and secure than ETX.