Distributed dynamic replica placement and request redirection in content delivery networks
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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

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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


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