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HIGHLIGHT - Connectivity-Through-Time Protocol for Wireless Adhoc Mobile Networks

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In a number of applications, remote devices must be deployed as adhoc wireless networks, which must operate under dynamics connectivity conditions. An example is a deployment of a team of mobile robots in remote building suspected of radiation contamination. The team cooperatively scans the building and builds its radiation profile prior to human operators entering the building in suitable protective gear. In this case, the robots must communicate with each other to coordinate their operation and also to communicate with the human operators located away from the scene. The current wireless technologies are inadequate for such operation for a number of reasons. The wireless networks require an infrastructure of access points through which the nodes communicate, and such infrastructure is not feasible to setup such access points in the above application. Without infrastructure the node can only communicate with the ones that are in the wireless range. The current methods based on Internet Protocol treat connectivity changes as error conditions and do not handle network partitions.

To address the class of wireless adhoc mobile networks typified in the above example, we developed a new protocol called the connectivity-through-time protocol. Using this protocol, a set of nodes can form an adhoc network without an infrastructure. The nodes detect one another using User Datagram Protocol (UDP) and compute multihop connectivity between all pairs of reachable nodes, i.e, nodes that are reachable using the paths through other nodes. We also developed software to enable each node to act as a router to relay messages. Thus the reach of the network is significantly enhanced since the communication is no longer limited between pairs that are in direct wireless contact. The Transport Control Protocol (TCP) is used to transfer the messages using other nodes as routers.

The second component of the protocol is based on a novel concept of connectivity. Two nodes are connected-through-time if there is a path via the wireless links and in-time, where each node it connected to itself in-time. Our protocol buffers the message suitably if there is no path to the destination and delivers it as new connections are formed. Using the parameters of time-to-live and connection-time, we proved that the messages will be delivered if there is connectivity-through-time. For example two robots working in areas that are connected at any time can use a third robot to deliver messages using this protocol. To our knowledge ours is the first protocol to achieve this. At present our protocol is implemented in C using sockets under windows and linux/unix environments.

CESAR - Center for Engineering Science Advanced Research Oak Ridge National Laboratory

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