Ad hoc Routing: Issues and AlgorithmsMobile Ad Hoc Networking (MANET)Goals for Ad Hoc RoutingGoals for Ad Hoc Routing (contd)Some Architectural ConsiderationsBrief Review on Shortest-path RoutingDesign Options in Ad Hoc RoutingDestination-Sequenced Distance-Vector Routing (DSDV)Slide 9Temporally-Ordered Routing Algorithm (TORA)PowerPoint PresentationAd Hoc On-Demand Distance Vector (AODV)Slide 13AODVDynamic Source Routing (DSR)Slide 16Further DiscussionsNew Trends in Ad Hoc RoutingAd hoc Routing: Issues and Algorithms•Why we study this paperidentify the issues of routing support in mobile ad hoc networksunderstand some design options for ad hoc routing support schemesalgorithm overviews of a few algorithms•New trends in ad hoc routingMobile Ad Hoc Networking (MANET)•No backbone infrastructure, typically operate over a single wireless channel•dynamic topologies: nodes are free to move arbitrarily•bandwidth-constrained, variable capacity links•energy-constrained operation•limited physical security•may have both unicast and multicast/broadcast traffic •typically assume reliable broadcast at the MAC/link layer•in the near term, MANET functions as stub networks (RFC2501): all traffic carried by MANET nodes will either be sourced or sinked within the MANETNOT as transit networks carrying traffic that enters and then leaves MANETGoals for Ad Hoc Routing•Near-term goal (RFC2501):provides for effective operation over a wide range of mobile networking “contexts” (i.e. a set of MANET characteristics)supports connectionless IP service: IP layer mobile routingreacts efficiently to topological changes and traffic demands while maintaining effective routing in a MANET context•Qualitative properties of MANET routing protocols:distributed operation: no centralized solutionloop-freedom: avoid problems such as a small fraction of packets spinning around in the net for arbitrary time periodsdemand-based operation: routing algorithms adapt to the traffic pattern in the net on a demand or need basisproactive operation: flip-side of demand-based operationsecurity, sleep period operation, unidirectional link support.Goals for Ad Hoc Routing (contd)•Network contextnetwork size (# of nodes), network connectivity (avg degree of a node), topological rate of change, link capacity, fraction of unidirectional links, traffic patterns, mobility (more on topological correlation), fraction & frequency of sleeping nodes•Quantitative metrics to assess ad hoc routing protocols:end-to-end data throughput and delayroute acquisition time: of particular concern with on demand routing algorithmspercentage of out-of-order deliveryefficiency: internal measure of its effectiveness•average number of data bits transmitted/data bit delivered•average number of control bits transmitted/data bit delivered•average number of control and data packets transmitted/data packet deliveredSome Architectural Considerations•Link level operationability to detect link appearances & failures in the presence of changing topology:•periodic probing using overhead packets (faster link status sensing)•lack of link-level ACKs of transmitted message packets (slower sensing, no overhead)•shortest path routing: is it worth the cost ?changing topology: slow versus fastcongested network: light versus heavyhow to handle the gray area ? adaptive•hard state versus soft stateBrief Review on Shortest-path Routing•Internet supports shortest-path routing•Properties for shortest path:subpaths of shortest paths are shortest pathsthe weight of a shortest path is the sum of the weights of its subpaths•Dijkstra’s algorithm: builds up a shortest path tree by computing the weighted breadth first tree from the source•Bellman Ford algorithm: builds a shortest-path tree by incrementally expanding the permissible set of nodes that are allowed to be intermediate hops•Distributed Bellman Ford Algorithm•distance vector and link state routingdistance vector: exchange vectors of distance estimates to destinations (e.g. RIP)link state: maintain the entire network topology at all routers (OSPF)Design Options in Ad Hoc Routing•Who serve as routers:every mobile host is a routera subset of the nodes are routers (e.g., due to energy concerns)every host is a router but only a subset of routers are used to generate routes (virtual backbone concept)•what is the neighborhood info to propagatelink state, distance vectors, known routes•metrics for route computationweighted shortest path, interference metrics, congestion metrics, power/energy metrics, throughput metrics •how many routes are maintainedsingle route for a source-destination pairmultiple routes for a src-dest pair•when to generate routesstatic versus on demandDestination-Sequenced Distance-Vector Routing (DSDV)•Based on the Bellman Ford routing algorithm with improvements such as freedom from loops in routing table•each node maintains a routing table recording all of the possible destinations and the distance to each destinationeach entry is marked with a sequence number assigned by the destination node•routing tables are periodically transmitted throughout the network •route updates via two types of packets:full dump packets carrying all available routing infoincremental packets carrying the change only since last full dumpDestination-Sequenced Distance-Vector Routing (DSDV)•Operations using sequence numberassociate monotonically increasing sequence number with the neighborhood update information. When info about a destination is being passed, the latest sequence number generated by that destination is used. This enables source nodes to distinguish fresh info from stale infouse sequence numbers to make routing loop-free•each node generates an even sequence number every time it propagates its neighborhood update•whenever a node detects a loss of connectivity with a neighbor, it creates a neighborhood update, with an odd sequence number that is generated by incrementing the known seq number for the neighborhood by 1•if the destination generates a new neighborhood update, it receives precedence over the loss of connectivity updatereduce the frequency of updates by using some stability heuristics: damping route update propagation by an amount of time it takes for a route to settle once a change has been