Scribble: an efficient reliable manycast protocol for ad-hoc networks

The problem of efficient message delivery to multiple nodes has been widely studied for ad-hoc networks, be it sensor or mobile ad-hoc networks (MANETs). We are concerned with deterministic delivery guarantees, i.e. the delivery ratio for any given message is guaranteed not to fall below a threshold specified for that message. This threshold can be considered to take the special case value of 100% when message delivery is guaranteed to all nodes. Guaranteeing delivery to all in a group, however desirable, often involves making a simplifying assumption that no destination node leaves the group nor crashes during an execution of the protocol. However, the nodes that make up an ad-hoc network are prone to failures and are likely to leave the group, something which undermines the validity of the assumption. We outline a protocol, called Scribble, which permits the minimum threshold to be less than 100%, thus allowing a few nodes to depart or crash during the execution. More precisely, it provides what we call k-deterministic delivery guarantees, where delivery is guaranteed to at least k destination nodes. The value of k is chosen by the application is required to be a realistic value. Such a service is called manycast.