A tunneling approach to routing with unidirectional links in mobile ad-hoc networks

Mobile ad hoc networks (MANETs) consist of a set of similar mobile nodes, communicating with each other using wireless links. As a node may not be able to directly reach every other node, a packet may need to traverse multiple wireless links from its source to its destination. Unidirectional links can occur in such networks. Several existing routing protocols implicitly assume bidirectional links when making their routing decisions. Not using unidirectional links can lead to sub-optimal routes. A tunneling solution to allow efficient operation in ad hoc networks with unidirectional links is presented. The tunneling solution uses information gathered by the routing protocol to tunnel packets from the end-point of the unidirectional link to its source. A naive implementation of tunneling could lead to loops in the system and a deluge of packets. This is because when ACKs (acknowledgments) for link layer messages are tunneled across unidirectional links, ACKs for them may end up being generated recursively. The solution presented here prevents such a packet explosion from occurring.