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

3. Paper Information 3Paper Summary- WINC- Nile University

4. Outline Paper Information Motivation Problem Statement Results Main Contribution Strengths, Weakness and limitations Future Works 4Paper 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 5Paper Summary- WINC- Nile University

6. Outline Paper Information Motivation Problem Statement Results Main Contribution Strengths, Weakness and limitations Future Works 6Paper 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 7

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) 8Paper Summary- WINC- Nile University

9. Problem Statement N4N4 N4N4 N3N3 N3N3 N2N2 N2N2 N1N1 N1N1 S S Only the source transmit a copy of the file F 9Paper Summary- WINC- Nile University

10. Problem Statement N4N4 N4N4 N3N3 N3N3 N2N2 N2N2 N1N1 N1N1 S S Any node could transmit a copy of the file F 10Paper Summary- WINC- Nile University

11. 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 11Paper Summary- WINC- Nile University

12. 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 12Paper 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 a k (i) that source will transmit newest version of F to node “i” Transmission is always successful Node deletes old version when receiving new ones 13Paper Summary- WINC- Nile University

14. Non Cooperative nodes Probability that node “i” receives the newest version of F in a slot p k (i) = q(i) a k (i) Probability that node “i” in state k: k (i) Average number of nodes in state k 14Paper 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 15Paper Summary- WINC- Nile University

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

17. Non Cooperative nodes System Utility U(k) is having file F of age k in the system 17Paper 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) 18Paper 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 19Paper 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 p 1 = (1-q) = (q,…,q) –(b) if Nq/q k +1< V < Nq/q (k-1) +1 for some k =1,…K, the optimal file management policy is p K (q(C-k)) = (q,0…,0,1-q(C-k),q,…,q) –(c) if V ≤ Nq/q (K-1) +1 any file management policy p K ( (C-k))=(p,0,….,0,P K ) 20Paper Summary- WINC- Nile University

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

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

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 23

24. Cooperative Nodes Proposition 4: –Assume Certain assumptions, Then {Y n } n is an homogenous irreducible and aperidoic Markov chain on ɛ. It is positive recurrent if there exist an integer M 0 and ɵ > 0 such that ɵ k (k) ≥ 0 for all k ≥ ɵ for all k ≥ M 0 and i = 1,……,N –Y n is the state of node I just before time t n. Paper Summary- WINC- Nile University 24

25. Cooperative Nodes Proposition 5 As m→∞, ɵ m in “ ɵ m+1 = m ( ɛ m +(MV-Y m ))” converges with probability one to a * the optimal static policy (Proposition 1) Paper Summary- WINC- Nile University 25

26. Outline Paper Information Motivation Problem Statement Results Main Contribution Strengths, Weakness and limitations Future Works 26Paper 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 27

28. Outline Paper Information Motivation Problem Statement Results Main Contribution Strengths, Weakness and limitations Future Works 28Paper 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 29

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 30

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

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

33. Future Work As suggested by the authors –Multi Source – Multi Files Paper Summary- WINC- Nile University 33 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)

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