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Distributed Dynamic Replica Placement and Request Redirection in Content Delivery Networks. Advisor : Ho-Ting Wu Student : Yu-Chiang Lin Date:2011/5/30. OUTLINE. CDN introduce Distributed Dynamic Replica Placement Cloning of a replica Replica removal Redirection Future work

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distributed dynamic replica placement and request redirection in content delivery networks

Distributed Dynamic Replica Placement and Request Redirection in Content Delivery Networks

Advisor : Ho-Ting Wu

Student : Yu-Chiang Lin

Date:2011/5/30

outline
OUTLINE
  • CDN introduce
  • Distributed Dynamic Replica Placement
  • Cloning of a replica
  • Replica removal
  • Redirection
  • Future work
  • Reference

 Page 2

outline1
OUTLINE
  • CDN introduce
  • Distributed Dynamic Replica Placement
  • Cloning of a replica
  • Replica removal
  • Redirection
  • Future work
  • Reference

 Page 3

cdn introduce
CDN Introduce

Fig:Server Farm(source from EBU technical review)

 Page 4

cdn introduce1
CDN Introduce
  • Consider TCP transmittion,throughput may affect by latency or packet lost。

 Page 5

cdn introduce2
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

cdn introduce3
CDN Introduce

Fig:Content Delivery Network(source from EBU technical review)

 Page 7

cdn introduce4
CDN Introduce

Fig:Content Delivery Network

 Page 8

cdn introduce5
CDN Introduce
  • Four Important technique
  • 1.Content route
  • 2.Content distribution
  • 3.Content store
  • 4.Content management

 Page 9

cdn introduce6
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

outline2
OUTLINE
  • CDN introduce
  • Distributed Dynamic Replica Placement
  • Cloning of a replica
  • Replica removal
  • Redirection
  • Future work
  • Reference

 Page 11

distributed dynamic replica
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

problem formulation
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

cloning of a replica
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

cloning of a replica1
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

cloning of a replica2
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

cloning of a replica3
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

replica removal
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

redirection
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

redirection1
Redirection

Fig. A model for the redirection scheme

 Page 20

outline3
OUTLINE
  • CDN introduce
  • Distributed Dynamic Replica Placement
  • Cloning of a replica
  • Replica removal
  • Redirection
  • Future work
  • Reference

 Page 21

future work
Future Work
  • comparison of different settings of the Umid
  • observe dmax and add remove replica relationship

 Page 22

reference
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