Location Services for Geographic Routing Geographic Routing l

Location Services for Geographic Routing

Geographic Routing l Three major components of geographic routing: Ø Location services (dissemination of location information) Ø Forwarding strategies Ø Recovery schemes

Problem Construct and maintain a location database. l Who keep track of whom? l Ø Some for Some Ø Some for All Ø All for Some Ø All for All

Location Database Distributed Information Structure l Two major operations l Ø Information Inform/Update (write) Ø Information Request/Query (read) l Question Ø Inform set = ? Ø Query set = ?

Inform Set l X stores its location information in every node in Inform-set(x). x Inform-set(x)

Query Set l y consults nodes in Query-set(y) for location information. x y Query-set(y)

Requirement Inform-set(x) ∩ Query-set(y) ≠ Φ for all x, y x Inform-set(x) y Query-set(y)

A Brute-Force Scheme All for All l Inform-set(x) = {all nodes} l Query set(y) = {y} l Example: DREAM l

Quorum-Based Location Database: Basic Idea U = A set of nodes l Quorum: any subset of U l Quorum system: a collection of pair-wise intersecting quorums l Inform-set(x) = any quorum l Query set(y) = any quorum l Design Issues: construction and maintenance of U and a quorum system l

Example Quorum System Quorum = one row + one column 1 4 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

A Quorum-Based Location Service l Zygmunt J. Haas and Ben Liang, “Ad Hoc Mobility Management With Uniform Quorum Systems, ” ACM/IEEE Trans. On Networking, April 1999. l Ben Liang and Zygmunt J. Haas, “Virtual Backbone Generation and Maintenance in Ad Hoc Network Mobility Management, ” INFOCOM 2000.

U=? l l l U = a set of nodes such that every node is within r-hops of U. Called r-virtual backbone. Called dominating set if r = 1.

Backbone Generation Similar to domination set generation l Nodes: Backbone, Bridge, Covered, Uncovered l backbone

Constructing a backbone: basic idea Initially, Backbone contains a single node. l Bridges keep entering Backbone until no more bridges. l Backbone

Required for the algorithm r-zone: the neighborhood within r hops l Every node maintains its r-zone l Ø e. g. using the link-state algorithm.

Maintenance of Backbone l If network topology changes Backbone changes

Quorum-Based Location Database U = {nodes in backbone} l Quorum: a subset of U l Quorum system: a collection of pair-wise intersecting quorums l Inform-set(x) = any quorum l Query set(y) = any quorum l

Maintenance of Quorum System Backbone may change l Quorum system may change l Maintenance of quorum system is nontrivial l

Conclusion Location services based on Quorum Systems seem too complicated. l So? l Probabilistic/Randomized Quorum Systems

Randomized Quorum Systems l l l Malkhi et al. , “Probabilistic Quorum Systems, ” Information and Computation 170, 184– 206 (2001). Also, PODC 1997. Zygmunt J. Haas and Ben Liang, “Ad-Hoc Mobility Management with Randomized Database Groups, ” ICC 1999. Jiandong Li, Zygmunt, J. Haas, and Ben Liang, “Performance Analysis of Random Database Group Scheme for Mobility Management in Ad hoc Networks, ” ICC 2003. S. Bhattacharya, “Randomized Location Service in Mobile Ad Hoc Networks, ” MSWi. M'03. H. Lee, J. L. Welch, N. H. Vaidya, “Location Tracking Using Quorums in Mobile Ad Hoc Networks, ” Aug 2003.

Basic Result [Malkhi et al. , 1997] U = a given set of nodes. l 0 ≤ p ≤ 1. l Random quorum of size k: any randomly selected subset of U of size k. l Given U and p, it is possible to choose k such that for any two random quorums, A and B, of size k, Prob(A ∩ B ≠ Φ) ≥ p. l

Random-Quorum-Based Location Database [Haas and Liang, ICC 1999] l l l U = {nodes in a virtual backbone} Ø These nodes serve as location servers Inform set(x) = any random quorum of size k. Query set(x) = any random quorum of size k. Access strategy: repeat queries until success. Performance studies

Performance Analysis [Li et al, ICC 2003] l l l Update cost Query cost Total cost Ø Ø Ø l l Update rate (λu) Query rate (λq) How does total cost depend on (λq / λu) and quorum size? Optimum quorum sizes Different query strategies

Randomized Location Service [ S. Bhattacharya, MSWi. M'03] l Two schemes for constructing a quorum: Ø Ø l l l 1: randomly choose k nodes 2: randomly choose a path of k nodes Similar accuracy for dense networks. Quorum size: depends on desired accuracy. Lower communication cost and query delay time for scheme 2.

Location Tracking Using Quorums [Lee, Welch, Vaidya, Aug 2003] l l l Comparing three kinds of quorum systems 1 2 3 4 U = {1, 2, …, n} 5 6 7 8 Biquorum system Ø Ø Ø l l l 9 10 11 12 Update quorums 13 14 15 16 Query quorums Update quorum ∩ Query quorum ≠ Φ 9 4 8 10 11 12 13 14 15 16 Traditional quorum system Random-quorum-based performs best

GLS: Grid location Service l l “A Scalable Location Service for Geographic Ad hoc Routing” J. Li, J. Jannotti, D. Couto, D. Karger, R. Morris MIT Mobicom 2000

Model l Dense deployment of nodes in a rectangular area Nodes have unique ID Nodes know their own location information

Geographic Hierarchy of the Network order-2 not order-2 order-3 order-1

Location Servers l Every node maintains its current location in the following location servers: Ø Ø Every node in the same order-1 square One node in every sibling order-2 square One node in every sibling order-3 square, etc.

Who knows whom?

Selecting Location Servers l If node x has a server in an area A, it is: f(x, A) = the node in A whose ID is circularly closest to x from the above. 4, 9, 15 17 11, 19, 35 39, 45, 50, 51

x y

Query: where is x? l l l y asks y’ =f(x, order-1(y)) y’ asks y’’=f(x, order-2(y’)) y’’ sks y’’’=f(x, order-3(y’’)) y’’’ l l Does y know y’? Does y’ know y’’? Does y’’ know y’’’? Answer: yes y’’ y’ x y

Query: where is x? 29 39 49 33 44 17 19 38 55 24 30 28 40 45 41 56 15

x y

How does x update Location Information? l x sends an update message to each area. Who is supposed to know x?

Home-Region Based Location Service l Each node x is assigned a home region H(x). Every node in H(x) serves as x’s location server. H(x) x x

Combining GLS with Home-Region l “A Scalable Location Management Scheme in Mobile Ad-hoc Networks, ” LCN 2001 l “SLALo. M: A Scalable Location Management Scheme for Large Mobile Ad-hoc Networks, ” WCNC 2002

SLALo. M l Unit square, order-1 square, order-2 square, etc.

SLALo. M l Each node has a home region (blue shade) in each order-1 square. y xu z

SLALo. M l x, y, z know of u’s whereabouts to the accuracy of unit square, oder-1 square, order-2 square, respectively. y xu z

SLALo. M l l x: a node in one of u’s home regions If u and x are in the same order-k square, but different order-(k-1) squares, then x knows which order-(k-1) square contain u. x u Order k-1 Order k