Outline Paper Information Motivation Problem Statement Results Main Contribution Strengths, Weakness...

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Distributed Storage Management of Evolving Files in Delay Tolerant Ad Hoc Networks

Eitan Altman, Philippe Nain, Jean-Claude Bermond

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Paper Summary- WINC- Nile University

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Outline

• Paper Information • Motivation• Problem Statement • Results • Main Contribution • Strengths, Weakness and limitations• Future Works

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Paper Information

Item Information

Conference IEEE INFOCOM 2009

Date April 19-25, 2009.

Place Rio de Janeiro, Brazil

Authors Eitan AltmanPhilippe NainJean-Claude Bermond

History Previous Research Report they have done

http://www.ieee-infocom.org/

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Outline


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Motivation

• Examine Different ways in distributing files which change dynamically. “In Delay tolerant Network”

• Generic Examples– File change from time to time(weather forecasting)– Backup files– Software update patches

• Example Standard:– RSS– Atom Syndication Format

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Outline


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Problem Statement

• The need to send an updated version of file to N nodes to be stored; these nodes are mobiles and contact time are exponentially distributed.

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Problem Setting

• N nodes • One Source Node• One File That is need to be updated

regularly• Nodes may be cooperative or not • File management policy (Static vs.

Dynamic)

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Problem Statement

N4

N3

N2

N1

S

NON- COOPERATIVE NODES

Only the source transmit a copy of the file F

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Problem Statement

N4

N3

N2

N1

S

COOPERATIVE NODES

Any node could transmit a copy of the file F

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Problem Statement

• Node at state 0; doesn’t have a copy of the file

• Node at state 1; have the resent copy of the file

• Node at state 2,3,4,5,….,K have an older, more older, etc…

• After state K node Return to State 0

NODE STATE

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Problem Statement

• Set of rules specifying whether the source and a node (or two nodes)should communicate.

• Policy is static if decision doesn’t depend on the state of the node

FILE MANAGEMENT POLICY

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Non Cooperative nodes

• Time Slot [t,t+1), t ≥ 0• Probability q(i) that node “i” meets the

source• Probability ak(i) that source will transmit

newest version of F to node “i”• Transmission is always successful • Node deletes old version when receiving

new ones

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• Probability that node “i” receives the newest version of F in a slot

• pk(i) = q(i) ak(i)

• Probability that node “i” in state k: ᴨk(i)

• Average number of nodes in state k

N

ikk KkiX

1

,......,1,0),(

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Performance Metrics – Expected number of copies – Expected age of the copies

Power Consumption (Q)

Expected number of transmission during a slot

1XQ

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Assume nodes are homogenous…

q(i) = q ; ak(i) = ak

Objective 1 FIND AN OPTIMAL FILE MANAGEMENT POLICY WHICH

MAXIMIZES THE SYSTEM UTILITY GIVEN A POWER CONSUMPTION CONSTRAINT

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System Utility

U(k) is having file F of age k in the system

K

kk kUXpC

1

)()(

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Results

• Proposition 1– If Nq ≤ V then p* = q is the optimal solution;

otherwise p* = V/N is the optimal solution or, equivalently, p* = min(q,V/N)

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Results

• Proposition 2– Under the assumption that the utility function

U: {1,…,L}→ R+ is non-increasing there exists an optimal threshold policy

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Results• Proposition 3

– Under the assumption that the utility function U: {1,…,L}→ R+ is non-increasing, the following results hold:

– (a) If Nq < V the optimal file management policy is p1 = (1-q) = (q,…,q)

– (b) if Nq/qk +1< V < Nq/q(k-1) +1 for some k =1,…K, the optimal file management policy is pK (q(C-k)) = (q,0…,0,1-q(C-k),q,…,q)

– (c) if V ≤ Nq/q(K-1) +1 any file management policy pK ( (C-k))=(p,0,….,0,PK)

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Numerical Results

U(k) =1N = 100V =20K = 5

U(k) =1N = 100V =10K = 5

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Numerical Results

U(k) =1/kN = 100V =20K = 5

U(k) =1/kN = 100V =10K = 5

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Cooperative Nodes

• Recap: nodes are allowed to share a copy of file F between each others

• Node may only delete the version of F when it receives a new version so K = ∞

• System with two events– Creation of a new version of F– File transferring

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Cooperative Nodes

• Proposition 4:– Assume Certain assumptions, Then {Yn}n is an

homogenous irreducible and aperidoic Markov chain on ɛ. It is positive recurrent if there exist an integer M0 and ɵ > 0 such that ɵk(k) ≥ 0 for all k ≥ ɵ for all k ≥ M0 and i = 1,……,N

– Yn is the state of node I just before time tn .

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Cooperative Nodes

• Proposition 5

As m→∞, ɵm in “ɵm+1 = ᴨm (ɛm +(MV-Ym ))” converges with probability one to a* the optimal static policy (Proposition 1)

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Outline


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Main Contribution

• Discuss static and dynamic policies to distribute single file and one source to N nodes

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Outline


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Limitations

– Assume perfect environment with successful transmission(no failure)

– Assume that file transmission will go through only one time slot for simplicity.(limited size of file)

– Assume fixed number of node, although he handled briefly the intermittently available of nodes (Remark 2.2)

– Assume one source exist and only one file

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Strengths

• Logical Sequence in discussing the problem– Begin with non cooperative static case then

dynamic cast till reaching cooperative dynamic case

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Weakness

Page 7, Second Paragraph in Quantitative performance, mistake in condition k ≥ 1

Which may confuse the reader

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Outline


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Future Work

• As suggested by the authors– Multi Source – Multi Files

• Other Suggestion• No Perfect transmission in sparse network• Bigger file (More than one time slot)• Dynamic Environment (Dynamic number of nodes) each version

may needed to be distributed to subset or superset of N nodes • Usage of intermediate nodes to only translate file to certain node

(impact in performance) , and then delete file. When delete it? What about security? Do we need this?(DTN natural behavior)

• Do we need to transmit all the file or just the updated portion or just insert new data. (Impact on performance)

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Thank You

• Any Questions?

Outline Paper Information Motivation Problem Statement Results Main Contribution Strengths, Weakness...

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