Location-Based Routing Algorithm with Cluster-Based Flooding (LORA-CBF) employs two location services: Simple and Reactive. A Simple Location Service has been implemented for neighbors nodes, and for faraway nodes, a Reactive Location Service is employed. In LORA-CBF, the source node includes the location of its destination in each packet. The packet moves hop by hop through the network, forwarded along via cooperating intermediates nodes. At each node, a purely local decision is made to forward the packet to the neighbor that is geographically closest to the destination. However, location information by itself does not guarantee the transmission between neighboring nodes in vehicular ad-hoc networks. Mobility and contention of wireless media may cause loss of packets being transferred, and this is very important aspect to consider in the development of wireless routing algorithms. Here, the authors have addressed this problem by including a predictive algorithm in LORA-CBF.
TopIntroduction
The idea of using geographical information in highly mobile nodes is to improve packet forwarding decisions (Käsemann, et. al., 2002). Before forwarding a packet, a node using location information only needs information about the immediate neighbourhood and the position of the destination. However, as an essential prerequisite for location-based routing, a location service is needed from which a node can learn the current position of its desired communication partner. To preserve location information on other nodes in the network, each mobile node maintains a location table. This table contains an entry for every node in the network whose location information is known, including the node’s own location information. Three location services have been described in (Camp, Boleng & Wilcox, 2002): DREAM Location Service (DLS), Simple Location Service (SLS) and Reactive Location Service (RLS).
DREAM Location Service (DLS)
In the DREAM location service, each location packet updates the location tables containing the coordinates of the source node based on some reference system, the source node’s position, and the time the location packet was transmitted. Each mobile node in the ad hoc network transmits a location packet to nearby nodes at a given rate and to faraway nodes at another, lower rate. The rate a mobile node transmits location packets adapt according to when the mobile node has moved a specified distance from its last update location. Since faraway nodes appear to move more slowly than nearby mobiles nodes, it is not necessary for a mobile node to maintain up-to-date location information on them. Thus, by differentiating between nearby and faraway nodes, the overhead of location packets can be reduced.
Simple Location Service (SLS)
A node using the Simple Location Service transmits a location packet to its neighbours at a given rate. The rate a mobile node transmits location packets adapts according to location change, via a similar procedure used for nearby nodes in DLS. Each location packet in SLS contains up to E entries from the node’s location table and the E entries are chosen from the table in a round robin fashion. As multiple location packets are transmitted, all the location information a node contains is shared with its neighbours.
A node using SLS will also periodically receive a location packet from one of its neighbours. The node will then update its location table, based on the received table entries, in such a manner that location information with the most recent time is maintained.
Reactive Location Service (RLS)
In the Reactive Location Service (RLS), when a mobile node requires a location for another node and the location information is either unknown or expired, the requesting node will first ask its neighbours for the requested location information. If the node’s neighbours do not respond to the requested location information within a timeout period, the node will flood a location request packet in the entire network.
When a node receives a location request packet and does not know the requested location information, the node propagates the flood location request. If, however, a node receives a location request packet and the node’s location table contains the requested location information, the node returns a location reply packet via the reverse source route obtained in the location request packet. In other words, each location request packet carries the full route (a sequential list of nodes) that a location reply packet should be able to traverse in its header.
The advantage of using positional information in vehicular ad-hoc wireless networks (VANET) is that routing can be fully dynamic and distributed and the number of flooding packets observed in dynamic ad-hoc networks compared to non-positional algorithms is reduced.