distributed dynamic replica placement and request redirection in content delivery networks advisor :...
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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
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OUTLINE CDN introduce
Distributed Dynamic Replica Placement
Cloning of a replica
Replica removal
Redirection
Future work
Reference
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OUTLINE CDN introduce
Distributed Dynamic Replica Placement
Cloning of a replica
Replica removal
Redirection
Future work
Reference
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CDN Introduce
Fig:Server Farm(source from EBU technical review)
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CDN Introduce
Consider TCP transmittion， throughput may affect by latency or packet lost。
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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.
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CDN Introduce
Fig:Content Delivery Network(source from EBU technical review)
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CDN Introduce
Fig:Content Delivery Network
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CDN Introduce
Four Important technique
1.Content route
2.Content distribution
3.Content store
4.Content management
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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
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OUTLINE CDN introduce
Distributed Dynamic Replica Placement
Cloning of a replica
Replica removal
Redirection
Future work
Reference
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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 V∈ R autonomously decides on whether some of the replicas it stores should be cloned or removed.
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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 V∈ A for content c C∈
Umax, Umid, Ulow: load threshold
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Cloning of a replica Function add_replica(j, c)
1: lj,c =i V∈ A αij,c · xi,c
2: while lj,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 < VmaxR do
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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
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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
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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
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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.
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Redirection Based on this feedback users requests are directed
away from a replica in response to threshold events (if the replica load exceeds Umax or 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
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Redirection
Fig. A model for the redirection scheme
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OUTLINECDN introduce
Distributed Dynamic Replica Placement Cloning of a replica
Replica removal
Redirection
Future work
Reference
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Future Work comparison of different settings of the Umid
observe dmax and add remove replica relationship
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Reference [1] N. Bartolini, F. Lo Presti, and C. Petrioli, “Optimal dynamic r
eplica 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.