1、ECE 5970 02/24/2005,A Survey on Position-Based Routing in Mobile Ad-Hoc Networks,Alok Sabherwal,ECE 5970 02/24/2005,Overview,Introduction Location Services Distance Routing Effect Algorithm for Mobility Quorum-Based Location Service Grid location Service Homezone Forwarding Strategies Greedy Packet
2、Forwarding Restricted Directional Flooding DREAM LAR Hierarchical Routing Terminodes Routing Grid Routing Comparisons,ECE 5970 02/24/2005,Routing in MANET,Static vs. Mobile Flooding-based routing Reactive vs. Proactive Source routing vs. Table driven routing Flat vs. Hierarchical routing Non-locatio
3、n based vs. Location based routing,ECE 5970 02/24/2005,Position-based routing,Position-based routing algorithms eliminate some of the limitations of topology-based routing by using additional information. A location service is used by the sender of a packet to determine the position of the destinati
4、on and to include it in the packets destination address. Position-based routing thus does not require the establishment or maintenance of routes. (Forwarding Strategy),ECE 5970 02/24/2005,Location Services,In order to learn the current position of a specific node, the help of a location service is n
5、eeded. Difficult to get the position of location server! (Egg & Chicken) No guarantee for one position server in each ad hoc network. Location services can be classified according to how many nodes host the service Some-for-some Some-for-all All-for-some All-for-all,ECE 5970 02/24/2005,Location Serv
6、ices,Distance Routing Effect Algorithm for Mobility (DREAM)Quorum-Based Location ServiceGrid Location Service (GLS)Homezone,ECE 5970 02/24/2005,Distance Routing Effect Algorithm for Mobility (DREAM),Proactively disseminate location information Distance Effect : Closer nodes are updated more frequent
7、ly “age” field in location update Mobility Effect : rate of location update controlled by mobility No bandwidth wastage for no movement Routing policy If no entry for destination in table, flood Otherwise forward data to m neighbors in the direction of destination,ECE 5970 02/24/2005,* All for all a
8、pproach,ECE 5970 02/24/2005,Quorum Based Location Services 1 of 3,Known from information replication Update and request performed on different node subsets If subsets intersect up to date information can always be found,ECE 5970 02/24/2005,Quorum Based Location Services 2 of 3,A some-for-some scheme
9、 Node subset hosts position databases Virtual backbone between those nodes (non-position-based routing algorithm) Send position update and query to the nearest backbone node Backbone node contacts the nodes of a (usually different) quorum Timestamps to choose most current information Tradeoff: Quoru
10、m size(communication cost and resilience against unreachable backbone nodes),ECE 5970 02/24/2005,Quorum Based Location Services 3 of 3,How to deal with the movement of backbone node? The topology of the backbone will be rearranged If a backbone node has been disconnected from the network for more th
11、an a threshold amount of time, a new node will be chosen as the replacement,ECE 5970 02/24/2005,Grid Location Service (GLS),Geographic Forwarding- Each node maintains its position using GPS and broadcast HELLO packet to its neighbors,ECE 5970 02/24/2005,Geographic Forwarding more,Each node maintains
12、 a routing table for all nodes within two hops Forward a packet to the neighbor node closest to the destination* All for some approach,ECE 5970 02/24/2005,An Example of Grid,ECE 5970 02/24/2005,The Grid Location Service (Cont.),Three main activities Location server selection Location query request L
13、ocation server updateHandling Failures,ECE 5970 02/24/2005,Selecting Location Servers,Unique ID using hash function Select nodes with ID “closest” to its own ID “Closest” means the least ID greater than the nodes ID ID space is circular,ECE 5970 02/24/2005,Location Server Organization,ECE 5970 02/24
14、/2005,Location Query Request,The query request packet is forwarded to a node that is closest to the destination, within the order-2 square The packet is forwarded through the higher order grid square until it reaches the location server of the destination The destination responds directly with its d
15、estination to the source node,ECE 5970 02/24/2005,Location Server Update,Each node maintains two tables- A location table- A location cache Update packet is sent to location servers Update distance threshold,ECE 5970 02/24/2005,Location Query Failures,Two types of failures- A location server has out
16、-of-date informationSolution: use the old location information- A node moves out of its current gridSolution: forwarding pointers,ECE 5970 02/24/2005,Homezone,A virtual homezone where position information for a node is stored The position C of the homezone for a node can be derived by applying a wel
17、l-known hash function to the node identifier All nodes within a disk with radius R centered at C have to maintain position information for the node If the homezone is sparsely populated, R may have to be increased,ECE 5970 02/24/2005,Comparisons of Location Service,ECE 5970 02/24/2005,Forwarding Str
18、ategies,Greedy Packet ForwardingRestricted Directional FloodingHierarchical Routing,ECE 5970 02/24/2005,Greedy Packet Forwarding,MFR Most Forward within R It tries to minimize the number of hops a packet has to traverse in order to reach D NFP Nearest with Forward Progress The packet is transmitted
19、to the nearest neighbor of the sender which is closer to the destination Better than MFR Compass routing It selects the neighbor closest to the straight line between sender and destination,ECE 5970 02/24/2005,Greedy Routing Strategies,ECE 5970 02/24/2005,Greedy Routing Failure,ECE 5970 02/24/2005,Re
20、stricted Directional Flooding,DREAM Sender will forward the packet to all one-hop neighbors that lie in the direction of destination Expected region is a circle around the position of destination as it is known to source The radius r of the expected region is set to (t1-t0)*Vmax, where t1 is the cur
21、rent time, t0 is the timestamp of the position information source has about destination, and Vmax is the maximum speed that a node may travel in the ad hoc network The direction toward destination is defined by the line between source and destination and the angle ,ECE 5970 02/24/2005,DREAM,ECE 5970
22、 02/24/2005,Location-Aided Routing (LAR),Each node knows its location in every moment Using location information for route discovery Routing is done using the last known location + an assumption Route discovery is initiated when: S doesnt know a route to D Previous route from S to D is broken,ECE 59
23、70 02/24/2005,LAR - Definitions,Expected Zone S knows the location L of D in t0 Current time t1 The location of D in t1 is the expected zone Request Zone Flood with a modification Node S defines a request zone for the route request,ECE 5970 02/24/2005,LAR,ECE 5970 02/24/2005,Hierarchical Routing,Ter
24、minodes Routing TLR (Terminode Local Routing) It uses a proactive routing scheme if the destination is close to the source node. TRR (Terminode Remote Routing) TRR allows data to be sent to non-TLR-reachable destination,ECE 5970 02/24/2005,Terminodes Routing,ECE 5970 02/24/2005,Grid Routing,It is si
25、milar to Terminodes Routing A proactive distance vector routing is used at local level Intermediate Node Forwarding (INF) is used for long-distance routing,ECE 5970 02/24/2005,Comparisons of Forwarding Strategies,ECE 5970 02/24/2005,Work done,How to discover the position of the destination ? How to
26、forward the packets based on above ?,ECE 5970 02/24/2005,Results,All for some services like GLS in combination of greedy packet forwarding is the most promising in general position based routing. DREAM & LAR could be useful in situations where a small number of packets need to be transmitted very reliably.,ECE 5970 02/24/2005,References,Martin Mauve, et al, “A Survey on position based routing in ad-hoc networks “, IEEE Network Magazine 15 (6), pp. 30-39, November 2001.,ECE 5970 02/24/2005,Thank you!,
