Opportunistic routing has recently attracted
much attention as it is considered a promising
direction for improving the performance of wireless
ad hoc and sensor networks. With opportunistic
routing, intermediate nodes collaborate
on packet forwarding in a localized and consistent
manner. Opportunistic routing greatly
increases transmission reliability and network
throughput by taking advantage of the broadcast
nature of the wireless medium. In this article we
first illustrate the basic idea behind opportunistic
routing, and then categorize current research
work based on different criteria. We illustrate
how different protocols work, and discuss their
merits and drawbacks. Finally, we point out
potential issues and future directions in opportunistic
routing for wireless ad hoc and sensor
networks.