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Dynamic Routing in Mobile Ad Hoc Network. 報告者：呂佐鴻 指導教授：李鴻璋. What is Ad Hoc? In an ad hoc network, a set of wireless stations communicate directly with one another without using an AP or any connection to a wired network.
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Dynamic Routing in Mobile Ad Hoc Network 報告者：呂佐鴻 指導教授：李鴻璋
What is Ad Hoc? • In an ad hoc network, a set of wireless stations communicate directly with one another without using an AP or any connection to a wired network.
Position-based routing protocol use the geographic position of nodes to make routing decisions. • Location information can be obtained through GPS or some other type of positioning mechanism.
Position-based routing can be divided into two distinct tasks： • The location service (discovering the position of the destination) • The actual routing of data packets (based on location information)
Position or geographical routing thus allows radios to operate nearly stateless; nodes neither have to store routing tables nor transmit messages to keep routing tables up-to-date. • One potential weakness of this family of location-aware protocols is the dependence on GPS for obtaining one’s location.
There exist three common routing strategies for position-based routing – greedy forwarding, directed flooding, and hierarchical routing. • A node forwards a given packet to one (greedy forwarding) or more (directed flooding) one-hop neighbors that are located closer to the destination than the forwarding node itself.
Distance routing effect algorithm for mobility (DREAM) • DREAM is based on the observation that the greater the distance separating two nodes. • Source and intermediate nodes calculate the direction of destination D and, based on the mobility information about D, associate an angular range with the routing entry to D.
Distance routing effect algorithm for mobility (DREAM) • The direction toward the destination is determined by means of the so-called “expected region”. • A message is forwarded to all neighbors whose direction belongs to the selected range.
Distance routing effect algorithm for mobility (DREAM) • The neighboring hops repeat this procedure using their view for D’s position. • Nodes in DREAM broadcast position update messages to update the position information by other nodes.
Distance routing effect algorithm for mobility (DREAM) • A node can control the accuracy of its position information available to other nodes by • Modifying the frequency with which it sends position updates • Indicating how far a position update packet is allowed to travel before being discarded.
Distance routing effect algorithm for mobility (DREAM) • The distance effect is a reasonable paradigm when intermediate hops are allowed to update the position information carried in a packet. • DREAM works well in combination with an all-for-all location service that provides more accurate information close to the destination.
Distance routing effect algorithm for mobility (DREAM) • This reduces the size of expected region and thus the area in which the packet is flooded. • DREAM uses directed flooding to limit the flooding to the direction of the destination. • Directed flooding restricts routing redundancy which may prevent the routing protocol from discovering the shortest paths.
Location-aided routing (LAR) protocol • LAR assumes that data source node knows the location and roaming speed of the destination node. • The LAR protocol basically uses restricted flooding to discover routes. • Specifically, only the hosts in the request zone help forward route-searching packets.
Location-aided routing (LAR) protocol • S initiates a route discovery process, it should include the coordinates of the request zone in the packet. • A receiving host simply needs to compare it own location to the request zone to decide whether or not to rebroadcast the route-searching packet.
Location-aided routing (LAR) protocol • When D receives the route request packet, it sends a route reply packet back to S. When S receives the reply, the route is established. • If the route cannot be discovered within a specified time-out period, S can initiate a new route discovery with an expanded request zone.
Location-aided routing (LAR) protocol • One potential weakness of the protocol is that prior knowledge of the destination’s location may not always be available at the source. • The protocol may require mobiles to communicate their location more frequently, or enlist the aid of a distributed location service.
Location-aided routing (LAR) protocol • Furthermore, underlying the location-aided routing protocol is the notion that a route to the destination can be found by search in the general direction of the destination. • Terrain features such as buildings, hills, and foliage are, however, not considered.
