Distance-vector routing protocols for networks with unidirectional link

We first introduce a simple distance-vector protocol for routing in networks having unidirectional links. The protocol can be seen as an adaptation for these networks of the strategy as used in the popular RIP protocol. The protocol comprises two main algorithms, one for collecting "from" information, and the other one for generating and propagating "to" information. However, the traditional RIP approach has been a "busy" one because of the periodic sending of routing information even after the network has reached a stable state. We make further improvements on the simple protocol to get a message-thrifty variant. A routing information message is sent only when there is a change to the topology or when a link changes cost and only those affected entries need to be sent around.