ITR/SI - A Networking Protocol for Underwater Acoustic Networks

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We propose development of a network layer protocol necessary to increase the utility of acousticcommunications in the shallow water environment. Increasing attention has been given to collecting datafrom difficult to access coastal waters for diverse activities, to include scientific research, industrial andcommercial concerns, and military applications. The preponderance of activity has focused ondeveloping reliable methods for transmitting the information collected through the difficult time-varyingshallow water medium. However, current network layer protocols, which are responsible for determiningtraffic routing, do not provide for guaranteed quality of services. Current protocols also may causeunnecessary message delays.The delivery of traffic in an acoustic network is complicated by the excessive propagation delaysresulting from the speed of sound in water. The effect of this propagation speed is to cause an acousticnetwork connected by short hops to perform similar to a wire-based network with links betweenneighboring nodes of over 100,000 kilometers. However, the potential benefits and increased potentialfor application developments that stem from the implementation of wireless underwater networks make itworthwhile to explore means of mitigating the effects of the propagation delays.Central to the problem of route determination for network traffic is the discovery of the networkstopology from which network nodes extract next-hop information upon which to base traffic forwardingdecisions. Two principal methods are used for discovering the route information. Proactive routingmethods pre-compute route data before network traffic is generated, thus when traffic is submitted bynetwork applications the appropriate routes are already known. Reactive routing determines the routeinformation in response to traffic submissions. This method, referred to as on-demand routing, seeks tominimize route discovery traffic by only determining routes necessary to support actual traffic patterns.This routing information is cached to increase responsiveness to submitted traffic and adaptability totopology changes. Both methods have their merits; however, neither adequately supports resourceallocations necessary to assure guaranteed levels of service quality.We proposed a novel network protocol that provides many of the benefits of proactive routing yetretains the adaptability of reactive protocols. Our protocol is based upon a central master node whichperiodically probes the network for active participant nodes. In responding to the probes, the nodesprovide the master node with sufficient information for the master node to determine all possible datapaths through the network. From this information the master node makes all routing decisions for thenetwork and provides irnext-hoply information to each non-master node, thus reducing the workload onnon-master nodes. This information also enables the master node to optimize the allocation of traffic tonetwork paths providing for active management of delays insuring delay variance and data capacity arewithin the established quality of service commitments.Fundamental to this approach is the separation of control traffic from data delivery. This separationallows data to be transmitted without first having to wait for traditional handshake mechanisms to provideaccess to the channel. This separation significantly reduces the expected delay to which traffic issubjected resulting in potentially higher data throughput.Progress in network layer protocols will expand the usefulness of underwater acoustic networksbeyond applications that are limited to very low data rate traffic and non-time sensitive data types.Specific beneficiaries of this research activity include the Deployable Autonomous Distributed System,the SeaWeb Technology Demonstrations, the Autonomous Oceanographic Sampling Network, and theNational Oceanographic partnership Programs Front Resolving Observational Network with Telemetry(FRONT) project.