Geo Location Service CS218 Fall 2008

1. Geo Location ServiceCS218 Fall 2008 Yinzhe Yu, et al : Enhancing Location Service Scalability With HIGH-GRADE , MASS 2004, Oct 2004

2. What is a Location Service? • A pre-requisite of Position-Based Routing is a Location Service • Allows a source node to obtain the location of a destination before data traffic follows • Location Service is a cooperative service • Each node in the MANET stores the current locations of some other nodes in the network, serving as their location server • A node updates its location servers as it moves around • A node trying to communicate with another node queries that node’s location servers to get its current location

3. Basic Problem For a node B wishing to communicate with another node A, how to discover current location of A? • How does A choose a set of nodes as its location servers, and how to update these servers as A moves around? (Location Server Organization) • What exact information about A’s location are stored on its location servers? (Location Information Granularity) • How does B find appropriate server(s) of A to obtain its location?

4. Proposed : HIGH-GRADE • HIerarchicalGeographicalHash with multi-GRainedAddressDElegation • A better scheme that incorporates good design choices, and provides better scalability • Possible application: geo-routing in the urban vehicular grid

5. HIGH-GRADE divides a network area recursively into levels of “squares”. Each node chooses location servers around some hash points, one in each level of square. Each location server stores the information of “which next level square does A resides in ?”. A HIGH-GRADE Location Update

6. Location Info at Hash Points E G F D H C When there is no node at the exact location of the hash point, the update packet travels around the “perimeter” of the hash point and the location information is stored on all nodes on the perimeter.

7. B HIGH-GRADE Location Query • A querying node B uses the same hash functions to try potential location servers • Once a location server is found, it follows a series of servers at smaller and smaller area to pin-point A’s location • The total distance traveled by a location query message is proportional to the side length of A and B’s least common square A

8. Analysis: Model assumption • A common set of assumptions to analyze costs of maintaining and using a location service • A network with N nodes in an area of A • constant node density . • Average progress towards the destination point in each packet forwarding step is z. • Simplified random way-point mobility model with no pause time. Average node speed is v.

9. Metrics • Location Update Cost • Number of forwarding operations each node needs to perform in a second to handle the location update packets. • Location Query Cost • Number of forwarding operations each node needs to perform in a second to handle the location queries. • Storage Cost • Number of location records a node needs to store as a location server.

10. Summary of Results • Observations: • Design of a location service involves tradeoffs among all three metrics. • Not all schemes exploit the benefits of a localized traffic equally well. • For localized traffic HIGH-GRADE achieves impressive asymptotic scalability.

11. Main Innovation in High Grade • In an urban environment, the frequency of queries is orders of magnitude smaller than the frequency of updates - thus, updates dominate the cost • Update cost in High Grade is O ( vlog N ) because only the lowest level location server in the hierarchy is updated • In GLS the update cost is because the servers at all levels (from bottom to top) are updated. • Thus , High Grade scales to N, while GLS does not • This is the main innovation of the High Grade paper

12. Simulation • Compare GLS and HIGH-GRADE • Confirm analytical results • ns2 with CMU Monarch extensions • N = 100 ~ 600 • Node density fixed at 100/km2 • Transmission range is 250 m • Mobility model: random waypoint (w/o pause) • Maximum speed 10~30 m/s • Load • Each node generates 15 location queries for random destination nodes during a 300 sec simulation time

13. Location Update Cost vs. N and v