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Distributed Dynamic Replica Placement and Request Redirection in Content Delivery Networks

This paper explores a distributed scheme for dynamically placing and removing replicas in Content Delivery Networks (CDNs) to satisfy user requests while minimizing costs. It also discusses redirecting user requests based on replica load thresholds. Future work includes comparing different settings and observing distance constraints.

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Distributed Dynamic Replica Placement and Request Redirection in Content Delivery Networks

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  1. Distributed Dynamic Replica Placement and Request Redirection in Content Delivery Networks Advisor : Ho-Ting Wu Student : Yu-Chiang Lin Date:2011/5/30

  2. OUTLINE • CDN introduce • Distributed Dynamic Replica Placement • Cloning of a replica • Replica removal • Redirection • Future work • Reference  Page 2

  3. OUTLINE • CDN introduce • Distributed Dynamic Replica Placement • Cloning of a replica • Replica removal • Redirection • Future work • Reference  Page 3

  4. CDN Introduce Fig:Server Farm(source from EBU technical review)  Page 4

  5. CDN Introduce • Consider TCP transmittion，throughput may affect by latency or packet lost。  Page 5

  6. CDN Introduce • The Content Delivery Networks (CDN) paradigm is based on the idea to transparently move third-party content closer to the users • content is replicated on CDN servers which are located close to the final users so that users perceive a better content access service.  Page 6

  7. CDN Introduce Fig:Content Delivery Network(source from EBU technical review)  Page 7

  8. CDN Introduce Fig:Content Delivery Network  Page 8

  9. CDN Introduce • Four Important technique • 1.Content route • 2.Content distribution • 3.Content store • 4.Content management  Page 9

  10. CDN Introduce • CDN issue • 1) Deciding the kind of content that should be hosted (replica placement) • 2) selecting the best replica for a given user • 3) designing mechanisms for transparent redirection of the users requests to the best replicas  Page 10

  11. OUTLINE • CDN introduce • Distributed Dynamic Replica Placement • Cloning of a replica • Replica removal • Redirection • Future work • Reference  Page 11

  12. Distributed Dynamic Replica • Distributed scheme to allocate and deallocate replicas, so that the user requests are satisfied while minimizing the CDN costs in a dynamic scenario • This scheme always accounts for the current replica placement,adding replicas or changing replica location only when needed. • Each site j ∈ VRautonomously decides on whether some of the replicas it stores should be cloned or removed.  Page 12

  13. Problem Formulation • VA: access nodes • VR: CDN servers sites • d(i, j): user (access node) i to a replica j • dmax: distance threshold • xi,c: the volume of user requests originated at node i ∈ VAfor content c ∈ C • Umax, Umid, Ulow: load threshold  Page 13

  14. Cloning of a replica • Function add_replica(j, c) • 1: lj,c=i∈VA αij,c · xi,c • 2: whilelj,c/rj,c− Umax > 0 • 3: best_served = 0 • 4: best_distance = ∞ • 5: best_vr = undefined • 6: for all j’ ∈ ρ(j) s.t. rj,c < VmaxRdo  Page 14

  15. Cloning of a replica • 7: l’j,c=i∈α(j’) αij,c · xi,c • 8: total_distance =i∈α(j’)αij,c · xi,c · di,j’ • 9: if (l’j’,c < best_served) ∨ • 10: (l’j’,c= best_served ∧ • 11: total_distance < best_distance) then • 12: best_distance = total_distance • 13: best_served = l’j’,c  Page 15

  16. Cloning of a replica • 14: best_vr = j’ • 15: end if • 16: end for • 17: if best_vr = undefined then • 18: exit • 19: end if • 20: ask best_vr to add a replica  Page 16

  17. Cloning of a replica • 21: compute l’’bestvr,c= min(i∈α(bestvr) αij,c · xi,c, 1) • 22: lj,c= lj,c − l’’bestvr,c • 23: remove from the set of requests those that can be offloaded • 24: end while  Page 17

  18. Replica removal • A replica can be removed if (and only if) it serves no requests • A replica is removed only when it has not been serving requests for a time long enough to bring the exponential average down to zero.  Page 18

  19. Redirection • Based on this feedback users requests are directed away from a replica in response to threshold events (if the replica load exceeds Umaxor falls below Ulow) • As an example, an underloaded replica informs the redirection system which then tries to offload requests to some other replicas (if possible) • A perfect load balancing may be impossible due to the distance constraint  Page 19

  20. Redirection Fig. A model for the redirection scheme  Page 20

  21. OUTLINE • CDN introduce • Distributed Dynamic Replica Placement • Cloning of a replica • Replica removal • Redirection • Future work • Reference  Page 21

  22. Future Work • comparison of different settings of the Umid • observe dmax and add remove replica relationship  Page 22

  23. Reference • [1] N. Bartolini, F. Lo Presti, and C. Petrioli, “Optimal dynamic replica placement in Content Delivery Networks,” in Proceedings of the 11th IEEE International Conference on Networks, ICON 2003, Sydney, Australia, September 28–October 1 2003, pp. 125–130. • [2] F. Lo Presti, C. Petrioli, and C. Vicari, “Dynamic replica placement in content delivery networks,” in Proceedings of MASCOTS 05, September 2005. • [3] F. Lo Presti, C. Petrioli, and C. Vicari, “Distributed Dynamic Replica Placement and Request Redirection in Content Delivery Networks ,” in Proceedings of MASCOTS 07, 2008.  Page 23

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