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

1. Distributed Storage Management of Evolving Files in Delay Tolerant Ad Hoc Networks Eitan Altman, Philippe Nain, Jean-Claude Bermond

2. Outline • Paper Information • Motivation • Problem Statement • Results • Main Contribution • Strengths, Weakness and limitations • Future Works Paper Summary- WINC- Nile University

3. Paper Information Paper Summary- WINC- Nile University

4. Outline • Paper Information • Motivation • Problem Statement • Results • Main Contribution • Strengths, Weakness and limitations • Future Works Paper Summary- WINC- Nile University

5. 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 Paper Summary- WINC- Nile University

6. Outline • Paper Information • Motivation • Problem Statement • Results • Main Contribution • Strengths, Weakness and limitations • Future Works Paper Summary- WINC- Nile University

7. 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. Paper Summary- WINC- Nile University

8. 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) Paper Summary- WINC- Nile University

9. Problem Statement N3 N1 N4 N2 S Non- Cooperative Nodes Only the source transmit a copy of the file F Paper Summary- WINC- Nile University

10. Problem Statement N3 N1 N4 N2 S Cooperative Nodes Any node could transmit a copy of the file F Paper Summary- WINC- Nile University

11. Problem Statement Node State • 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 Paper Summary- WINC- Nile University

12. Problem Statement File management Policy • 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 Paper Summary- WINC- Nile University

13. 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 Paper Summary- WINC- Nile University

14. Non Cooperative nodes • 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 Paper Summary- WINC- Nile University

15. Non Cooperative nodes Performance Metrics • Expected number of copies • Expected age of the copies Power Consumption (Q) Expected number of transmission during a slot Paper Summary- WINC- Nile University

16. Non Cooperative nodes 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 Paper Summary- WINC- Nile University

17. Non Cooperative nodes System Utility U(k) is having file F of age k in the system Paper Summary- WINC- Nile University

18. 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) Paper Summary- WINC- Nile University

19. Results • Proposition 2 • Under the assumption that the utility function U: {1,…,L}→ R+ is non-increasing there exists an optimal threshold policy Paper Summary- WINC- Nile University

20. 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) Paper Summary- WINC- Nile University

21. Numerical Results U(k) =1 N = 100 V =20 K = 5 U(k) =1 N = 100 V =10 K = 5 Paper Summary- WINC- Nile University

22. Numerical Results U(k) =1/k N = 100 V =20 K = 5 U(k) =1/k N = 100 V =10 K = 5 Paper Summary- WINC- Nile University

23. 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 Paper Summary- WINC- Nile University

24. 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 . Paper Summary- WINC- Nile University

25. 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) Paper Summary- WINC- Nile University

26. Outline • Paper Information • Motivation • Problem Statement • Results • Main Contribution • Strengths, Weakness and limitations • Future Works Paper Summary- WINC- Nile University

27. Main Contribution • Discuss static and dynamic policies to distribute single file and one source to N nodes Paper Summary- WINC- Nile University

28. Outline • Paper Information • Motivation • Problem Statement • Results • Main Contribution • Strengths, Weakness and limitations • Future Works Paper Summary- WINC- Nile University

29. 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 Paper Summary- WINC- Nile University

30. Strengths • Logical Sequence in discussing the problem • Begin with non cooperative static case then dynamic cast till reaching cooperative dynamic case Paper Summary- WINC- Nile University

31. Weakness Page 7, Second Paragraph in Quantitative performance, mistake in condition k ≥ 1 Which may confuse the reader Paper Summary- WINC- Nile University

32. Outline • Paper Information • Motivation • Problem Statement • Results • Main Contribution • Strengths, Weakness and limitations • Future Works Paper Summary- WINC- Nile University

33. 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) Paper Summary- WINC- Nile University

34. Thank You • Any Questions? Paper Summary- WINC- Nile University