KAIST

On the problem of placing On the problem of placing Mobility Anchor Points in Wireless Mobility Anchor Points in Wireless

Mesh NetworksMesh Networks

Lei Wu & Bjorn Lanfeldt,

Wireless Mesh Community Networks Workshop, 2006

므리나 September 18, 2007

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OutlineOutline

Introduction

Problem description

Related work

Analysis of the problem in mathematical modeIdentification of the most important factors

Proposed approach

Simulation validation

Future work & conclusion

IntroductionIntroduction

Wireless mesh networks (WMN)Multi-hop wireless networks

Consist of wireless routers and mesh clients

Mobility of mesh clients in WMNLow mobility as compared to mobile ad-hoc networks

WMN Vs current fixed mobile networks

Unplanned topology

Wireless connection between mesh routers

Two geographically neighboring nodes can be very far from each other

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A Quick OverviewA Quick Overview

Mobile IPMN moves from a network coverage cell to another cell

Gets a CoA from the visited network

Registers the association between the CoA and the HA by sending a binding message

Hierarchical Mobile IPLocalized mobility management style to reduce the signaling overhead

Manages local and global mobility separately

To deal with local movement managementMAP is introduced

Entity that deals with the MIP handoffs

Local and global binding updates

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Problem DescriptionProblem Description

Mobility management techniques for seamless connectivityMobile IP – MIP

Inefficient in the cases of frequent migrations

Hierarchical mobility model schemes- Hierarchical mobile IP (HMIP)Provides faster handover for frequent migrations

Use of mobile anchor points (MAP) to group access points into different subnets

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*Traditional Hierarchical

Networks

Topology is structured like a tree

Placement of MAPs are predetermined to be at

the root nodes

Wired and stable links

Problem DescriptionProblem Description

Hard to use hierarchical mobility management schemes in WMN

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Where to place the MAPs ?

6 and 13 6 hops away13 and 5 4 hops away

Might be good for MAPBut . . . .

High delay due to 5 neighbors

MAPs placement is a

challenging problem

in WMN

Related WorkRelated Work

Not much research regarding the placement of MAPsFairly easy problem – place at the root node

Two different MAP placements of MAPs [13]Difference in handover delay

Research on other issues similar to the MAP placement problem

Placing different servers at different locations for better performances [14][15]

Focus is on maximizing the network capacity

In WMN, focus minimize the latency

Centrality type of problem [16][17][18]Based on central indices, the centrals of the networks can be determined

First used in social network analysis

Ex- co-citation networks most important and famous scientists

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Mathematical Modeling (1/4)Mathematical Modeling (1/4)

Mathematical definition of anchor point placementWMN as a simple undirected graph G= (V,E)

Edge delay

Shortest path from source to destination

Problem of selecting a set of nodes from V

and a set of sub-graphs from G so that each

acts as a root of to give minimum possible average delay

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1 2{ , ,....., }map map mapnv v v

1 2{ , ....., }nG G G mapiv

iG

Selection in 2 parts

*Formation of sub-graphs *Selection of the root nodes

,D De vi vjd

p es

D D

Mathematical Modeling (2/4)Mathematical Modeling (2/4)

Mathematical ApproachHandover delay calculation broken down into four parts

Movement detection delay

Router advertisement delay

Address configuration delay

Binding update delayLocal binding update delay

Global binding update delay

Total Handover Delay

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Local delays - not affected by the placement of MAPs Assumed to be constant const lreg procD D D

globaHO const BUL BUGD D D D

localHO const BULD D D

,4 4 2MAP HA

globalHO MN AR e e constAR MAP

D DD D D

,2 2MAP

localHO MN AR e constAR

DD D D

Mathematical Modeling (3/4)Mathematical Modeling (3/4)

Case 1 : only one MAP in the graph

Case 2 : If each AR is a MAP

Case 3 : Selecting g MAPs from graph topology

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Analysis

•Major part of the formula depends upon the average round trip time (RTT)

• Can be as small as 50% for the MAP in the centre of a graph rather than at the edge

• (a) shows the registration delay and the transmission delay between MN and AR

• (b) depends upon the transmissi-on delay between AR and MAP

• (c) is affected by the transmission delay between any MAP and any HA

•Avg. delay using 6MAPs is 12.2 and using MIP is 15 -> 18% reductionGood selection of MAP can

greatly reduce the delay

Mathematical Modeling (4/4)Mathematical Modeling (4/4)

Most important factors for the placement of MAPs

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Some Facts

• a good MAP selection can reduce the delay upto 50% in a simple graph

• HMIP with well selected MAP can reduce the handover delay as compared to MIP

• Local handover possibility m is the most important factor

Proposed IdeaProposed Idea

ApproachSteps:

Gather user mobility information

Based on this information, group mesh nodes into subnets

Size of the subnet > the max. one hop degree and < than max .two hop degree

Estimate the average local movement possibility m and record the number

of subnets g

Calculate the combine closeness centrality value

Select the node with largest combined closeness centrality in each subnet as the MAP

Forming benchmark for the provided solution-Select the MAPs randomly

Once the subnet is determined, a mesh node can be randomly selected as the MAP

Has only possibilities to find the best combination of MAPS

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Simulation ValidationSimulation Validation

Simulation ParametersOMNeT ++ with INET framework

Comparisons with random selection approach

Randomly positioned 15 mesh nodes

Possibility of a node to move to a different subnet is 30%

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Future Work & ConclusionFuture Work & Conclusion

Future WorkDistributed scheme to dynamically orm subnets

Not always possible to group meseh nodes together based on the mobility pattern

Dynamic MAP registration scheme Traffic thru MAPs

High delay when the # of visiting nodes becomes high

ConclusionMAP problem forming a tree structure in a random unplanned graph to minimize the handover delay

Hierarchical tree structures are easy to organizeChose the important nodes as root nodes

Transform the graph into a hierarchical tree structure

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QUESTIONS??

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