PowerPoint Presentation

Written byWei Shi, Joaquin Garcia-Alfaro, Jean-Pierre Corriveau

Mengfei PengSearching for a Black Hole in Interconnected Networks using MobileAgents and TokensAssumptionAgents: asynchronous, co-located/dispersed, carry a map of the network.Not assume FIFO on either nodes or links (first-in first-out)Network: un-oriented, asynchronous Hypercube, Torus, Complete network.Model: Token model

Agent

Black holeToken model

PortShared memory on a node

agentNode 1Node 2Node 3Token model

PortShared memory on a node

agentHow can we use a token?Cautious walk1,when the agent leaves the port,It puts a token at the port----this means Im going to the next nodeNode 1Node 2Node 3ABCDEF2,when the agent comes back,It picks up the token----that meansI come back safely

This port is dangerous, I dont go into it. I can stay here waiting or go to another way.I come back and the next node is safe.

A piece of software

Maybe A died here, its a dangerous port. I wont go into it.

Whiteboard model

PortShared memory on a nodeagentNode 1Node 2Node 3

Whiteboard model

PortShared memory on a nodeagentHow can we use a whiteboard?Cautious walk1,when the agent leaves the port,It writes Im going to the next node on the whiteboardNode 1Node 2Node 3ABCDEF2,when the agent comes back,It writes--I come back safely

A: Im going to the next nodeA: I come back safely and the next node is safe

Synchronous agents

Lets meet at 11:00OK, 11:00Asynchronous agents

Lets meetWhen?Whenever you can comeSure, I will try to come early

5 kilometers cost 50 minutes.6 kilometers cost 60 minutes.8 kilometers cost 80 minutes.77 kilometers cost 770 minutes.

5 kilometers cost 5 minutes.6 kilometers cost 150 minutes.8 kilometers cost 999 minutes.8 kilometers cost 3 minutes.

1 time unit1 time unit

1 time unit4 time unit100 time units

Co-located agents

Dispersed agents

SSSBypass technique1,use cautious walk to find a safe ring----no black hole in the ring

Dangerous ringSafe ring

SSSS

2,agent A is exploring the dangerous ring, and leave a token at port J2

Dangerous ringSafe ring

SSSS

3,agent B comes and sees As token, and moves As token to a safe port J1.

Dangerous ringSafe ring

SSSS

3,agent B goes to the safe ring and continues exploration.

Dangerous ringSafe ring

SSSS

3,agent B leaves its token at port P3, and explores the next node L

Dangerous ringSafe ring

SSSS

Question 1: what happens if there is an agent C comes?Dangerous ringSafe ring

SSSSS

Answer:Dangerous ringSafe ring

Question:When can we use the bypass technique?In a interconnected network, after finding a safe ring.

Whats the purpose of bypass technique?Allow more than one agent to explore the same ring at the same time.

Main resultsprove that, in the context of the Bhs problem in an asynchronous network with co-located agents, the token model can support the same cost as in the whiteboard modelSolutions to the Bhs problem for asynchronous torus, and complete network using tokens

a complete network, each node is linked to every other node by an edge.complexity2 co-located agents,edge labeled, n nodesDispersed agentsHypercube Algorithm Two Rings, Two tokensO(n)(n) exploringTorus Algorithm Cross Rings, 5 tokensO(n)(n) 3 agents, 7 tokens, oriented torusO(n) k (k > 3) agents,1 token per agent, oriented torusO(k2n2)Complete Networkalgorithm Take Turn,1 token(n) N agents, 1 token per agent ,an un-oriented complete network Kn.O(n2)