CMPT 886 Presentation

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CMPT 886 Presentation

• From chaining to P2VoD using clients outbound
  bandwidth to distribute media
• Savio Lau (saviol_at_cs.sfu.ca)
• June 8, 2004

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Outline

• Introduction
• Queuing policies
• Chaining standard and extended
• Chaining performance and issues
• P2VoD
• P2VoD performance and issues
• Conclusion

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Introduction

• Network I/O bandwidth is VoDs main operational
  constraint
• Queuing requests results in reneging
• Broadcasting is not always possible
• One solution is to use pipelining, by using
  client outgoing bandwidth to distribute media
• Sheu, Hua and Tavanapong introduced a pipelining
  idea called Chaining in 97

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Outline

• Introduction
• Queuing policies
• Chaining standard and extended
• Chaining performance and issues
• P2VoD
• P2VoD performance and issues
• Conclusion

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Queuing policies

• FCFS (First Come First Serve)
• Release video stream according to longest wait
  time
• MQL (Maximum Queue Length First)
• Choose first batch with largest number of clients

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Queuing policies

• FCFS-n
• Reserve fraction of server capacity for n most
  popular videos
• Other videos uses FCFS scheme
• MFQ (Maximum Factored Queue Length First)
• Stream released according to queue length
  weighted by best factor
• Best factor (associated access freq)-1/2
• MFQ is most fair amongst all schemes

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Outline

• Introduction
• Queuing policies
• Chaining standard and extended
• Chaining performance and issues
• P2VoD
• P2VoD performance and issues
• Conclusion

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Chaining terminology

• Video is divided into segments called R-blocks
• Numbered 1 to n
• v(i)i-th block of video v
• Clients are denoted Dm and Dn, where client Dm
  and Dn are playing back v(i) and v(j)
• Playback distance d(m,n) equals j-i, assuming jgti
• bd is the buffer size of clients

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Standard chaining

• Chains are formed from the server to a client,
  then from this client to the next and so on,
  similar to a waterfall
• A chain is closed when the first block is
  removed from buffer of the youngest child
• New clients join an open chain if the one is
  available, where d(m,n)ltbd
• Else new clients starts new chain, or enters
  queue if no bandwidth available

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Standard chaining
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Standard chaining
bd4 d(a,b)1 d(b,c)2
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Standard chaining
bd4 d(a,b)1 d(b,c)2 d(c,d)1 d(d,e)6
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Standard chaining
bd4 d(a,b)1 d(b,c)2 d(c,d)1 d(d,e)6 d(e,f)1
d(f,g)1
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Extended chaining

• Adds minimal wait time Wmin, time which each user
  has to wait
• Additional wait time follows exponential
  distribution (not used in algorithm)
• Uses Heuristic Extended Chaining (HEC) algorithm
  to determine when a client joins the chain
• HEC prolongs time until chain closure
• HEC is called for each new client arrival

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HEC algorithm terminology

• tnarrival time of nth client
• Tcurrent time
• keptnumber of clients retained
• keptmaxmaximum number of clients retained

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HEC algorithm

• ttnWmin
• if (t ? T) then return (kept0, tT)
• kept1
• while (kept lt n) and (kept lt keptmax)
• t min (tn-kept Wmin, t - t(bd))
• if (t ? T)
• t tprev
• return (kept, t) //end if
• else kept kept 1
• tprevt //end while
• if kept n then kept kept 1
• return (kept,t)

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HEC algorithm

• Case 1 ttnWmin ? T
• All clients waited past Wmin, all released
• Case 2 Some clients are kept
• Up to a maximum of keptmax clients are kept
• Increase kept until t ? T where tmin(tn-kept
  Wmin, t - t(bd))
• New chain starts at 2nd to last steps tt(bd)

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HEC algorithm example
Wmin4 t(bd)2
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Extended Chaining
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Batching, standard and extended chaining

• Number of I-gtQ transitions relates to server
  stress
• Extended chaining has least number of I-gtQ
  transitions

Standard chaining
Batching
Extended chaining
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Outline

• Introduction
• Queuing policies
• Chaining standard and extended
• Chaining performance and issues
• P2VoD
• P2VoD performance and issues
• Conclusion

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Chaining performance

• 2 Performance studies examined effects of
• FCFS and MFQ queuing with and without standard
  chaining
• MFQ queuing with extended chaining retaining 1 or
  2 clients
• Standard chaining with no queuing
• Network has 1 server and 220 clients connected
  as a 20-dimensional hypercube

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Chaining performance

• Negligible difference between standard chaining
  of MFQ and FCFS queuing
• Negligible difference between Extended chaining
  retaining 1 or 2 clients
• Extended chaining performs better than standard
  chaining
• Chaining with queuing performs better than
  without queuing

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Chaining performance

• Throughput (gt means higher throughput)
• extended chaining (MFQ)gt standard chaining (MFQ)
  gt chaining (no queuing) ? MFQ gt FCFS
• Fairness (gt means more fair)
• At high bandwidth extended chaining (MFQ)gt
  chaining (no queuing) or standard chaining (MFQ)
  gt FCFS
• At low bandwidth chaining techniques is least
  fair, even worst than MFQ

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Chaining performance

• Latency (lt means less latency)
• Extended chaining (MFQ) lt standard chaining (MFQ)
  lt MFQ lt FCFS
• Skew factor
• Chaining performance increases as the popularity
  of videos becomes more skewed

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Effects of communication bandwidth
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Effects of communication bandwidth
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Effects of communication bandwidth
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Effects of communication bandwidth
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Effects of storage I/O bandwidth
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Effects of storage I/O bandwidth
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Effects of storage I/O bandwidth
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Effects of request rate
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Effects of request rate
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Effects of request rate
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Effects of client storage size
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Effects of client storage size
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Effects of client storage size
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Effects of skew factor
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Issues with Chaining

• Not fault-tolerant
• Clients quitting the chain cause chain to be
  broken
• No recovery mechanism
• Affects extended chaining more than standard
  chaining
• P2VoD (Do, Hua and Tantaoui) addresses these
  issues 7 years later

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Outline

• Introduction
• Queuing policies
• Chaining standard and extended
• Chaining performance and issues
• P2VoD
• P2VoD performance and issues
• Conclusion

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P2VoD

• Similar to chaining where media stream is
  pipelined
• Introduces the concept of Generations
• Each client from chaining techniques becomes a
  group of clients, forming a video session
• Clients from each generation holds the same
  oldest R-block
• Provides joining, recovery and control

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P2VoD terminology

• MBmaximum cache in R-blocks for each client
• abXactual storage buffer used by client X
• tjXJoining time of client X
• addXIP address of client X
• G(X)generation client X belongs to

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P2VoD generations

• Clients in generation G(X)g will have the same
  oldest R-block in their cache
• Not all clients use the full size of the cache
• Client cache usage is determined by the time
  difference between the arrival time of client Y
  and the arrival time of client X which is the
  oldest member in a generation
• abXabY tjYtjX
• First generation G(X)1 has at most K members

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P2VoD generations
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P2VoD control protocol

• Each client
• Keeps IP address list of siblings
• Sends IP address of self and siblings to child on
  connection
• Sends IP address of self to parent
• Sends addX, G(X), texp to server upon joining

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P2VoD joining

• Case 1 No open video session
• Starts new video session if server has bandwidth
  available
• Rejected otherwise

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P2VoD joining

• Case 2 at least 1 open session
• 1. Contacts a random member of youngest
  generation GY to obtain list of GYs super
  generation GX
• 2. If GXs texp gt tjC then 3, otherwise 4
• 3. If possible, selects parent from GX, conform
  to cache rule of GY and receive stream
• 4. Form new generation below GY and select parent
  from GY if possible, otherwise try other video
  session. If failed-gtcase 1

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P2VoD joining

• Parent selection
• Round robin
• Smallest delay selection
• Smallest distance selection

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P2VoD joining
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P2VoD joining
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P2VoD joining
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P2VoD failure recovery

• Detect failure through heartbeat
• Recovery starts oldest orphaned client
• 1. Orphan client contacts sibling of parents and
  if one has bandwidth available switchover to that
  parent. Failed-gt2
• 2. Orphan client contacts server and connect
  directly to server if bandwidth exists.
  Otherwise session terminated.
• Repeat for each orphaned client

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P2VoD failure recovery
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P2VoD failure recovery
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Outline

• Introduction
• Queuing policies
• Chaining standard and extended
• Chaining performance and issues
• P2VoD
• P2VoD performance and issues
• Conclusion

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P2VoD performance
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P2VoD performance
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P2VoD performance
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P2VoD issues

• Does parent selection methods affect failure
  recovery and joining performance?
• Only G(X)1 is limited by K
• If bandwidth of clients are gtgt b, then tree width
  increases for each generation
• Failure of one parent can imply many orphans
• Each successive generation will need to contact
  larger number of parents for failure recovery

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P2VoD issues
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P2VoD issues

• Possible solution bandwidth reservation for
  failure recovery
• Allow as most J members per generation such that
  clients of any generation G(X) never exhausts all
  bandwidth
• How would J affect rejection probability? Or
  failure overhead?

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Outline

• Introduction
• Queuing policies
• Chaining standard and extended
• Chaining performance and issues
• P2VoD
• P2VoD performance and issues
• Conclusion

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Conclusion

• Extended chaining with queuing uses bandwidth
  most efficiently than other batching or chaining
  techniques
• A kept value of 1 is sufficient
• Additional retained clients has little
  performance gain
• Queuing method for chaining has negligible
  effects
• Chaining methodology is prone to failure

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Conclusion

• P2VoD addresses chaining issues about fault
  tolerance with the use of the concept of
  generations
• More extensive investigation is needed to examine
  the performance of P2VoD

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References

• S. Sheu, Kien A. Hua, and W. Tavanapong,
  "Chaining A generalized batching technique for
  video-on- demand," in Proc. of the IEEE Int'l
  Conf. on Multimedia computing and System, June
  1997, pp. 110-117.
• S. Sheu, K. A. Hua, and T. Hu, Virtual Batching
  A New Scheduling Technique for Video-On-Demand
  Servers, In Proc. Of Intl Conf. On Database
  Systems for Advanced Applications (DASFAA97),
  Melbourne, Australia, April 1997.
• Tai Do, Kien A. Hua, and Mounir Tantaoui, P2VoD
  Providing Fault Tolerant Video-on-Demand
  Streaming in Peer-to-Peer Environment to appear
  in the Proc. of the IEEE International Conference
  on Communications (ICC 2004), June 20-24 2004,
  Paris, France

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References

• A. Dan, D. Sitaram, and P. Shahabuddin, Dynamic
  batching policies for an on-demand video server,
  Multimedia Systems, Nov 1994. Vol 4. pp.112-121
• C.C. Aggarwal, J.L. Wolf, and P.S. Yu, On
  optimal batching policies for video-on-demand
  storage servers, in Proc. Of IEEE Intl Conf on
  Multimedia computing and System, Japan, June
  1996.
• Y. Guo, K. Suh, J. Kurose, D. Towsley, P2Cast
  P2P Patching Scheme for VoD Service, in WWW
  2003.
• V. Padmanabhan, H.Wang, P. Chou, Distributing
  Streaming Media Content Using Cooperative
  Networking, in NOSSDAV 2002.
• D. Tran, K. Hua, T. Do, A Peer-to-Peer
  Architecture for Media Streaming, in IEEE JSAC
  2003.

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Questions?