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Proxy-Assisted Techniques for Delivering Continuous Multimedia Streams
Lixin Gao, Zhi-Li Zhang, and Don Towsley
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Agenda
Related work Proxy-Assisted Video Delivery Architecture Proxy-Assisted Catching Proxy-Assisted Selective Catching Simulation results Conclusion
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Related WorkMulticast Techniques
Client pull Server-push
Batching Patching
Server-push
-> Typically designed for “hot” (frequently requested) objects
-> Fixed number of multicast channels
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Limitations of current technology
Server and network resources (Server I/O bandwidth and network bandwidth) are major limiting factors in widespread usage of video streaming over the internet
Need techniques to efficiently utilize server and network resources
Service latency and popularity of video object should be considered
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Advantages of proxy-assisted video delivery Latency reduction without increasing demand
on backbone network resources Need to store only the initial frames hence
feasible with large data volume I/O bandwidth requirement on proxy server is
insignificant, since responsible for limited number of clients
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ClassificationProxy-assisted video delivery architecture
Proxy-assisted catching
Proxy-assisted Selective catching
Proxy-assisted catching : Suited for “hot” video objects
Proxy-assisted selective catching : Even suited for “cold” (less frequently requested) video objects
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Advantages of proposed architectures
Reduce the resources requirements at central server
Reduce service latency experienced by clients
Assumptions
Client can receive data from 2 channels simultaneously
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Proxy-Assisted Catching Reduces service
latency by allowing clients to join an ongoing broadcast
Clients catch-up by retrieving initial frames using unicast channel from proxy
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Optimizing
Server and network bandwidth are major bottleneck. Hence reducing total number of channels required
Trade-off between -> Number of dedicated channels by server -> Storage space required by proxy
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Terms involved
N : No. of video objects on central server L : Length of video λ : Request rate (Poisson distribution) K : Server channels to broadcast video K* : Optimal number of server channels i : Video object no. j : Broadcasting frame
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Calculation
No. of proxy channels required :
Total no. of channels required :
Tradeoff between number of server channels and expected number of proxy channels required for catch-up
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Calculation contd..
Optimization problem :
Expected number of channels :
Optimal no. of server channels
Optimal no. of proxy channels
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Controlled Multicast Client pull technique Allows client to join the ongoing multicast if it requests with a
certain threshold time Ti
Else a new multicast channel is allocated
Proxy-assisted Controlled Multicast Proxy pre-store the initial Ti frames of video Missing portion of video is send separately through a
unicast channel Good technique for “cold” video objects
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Comparison with Proxy-Assisted Controlled Multicast Total no. of channels required for controlled
multicast is : For large value of λ no. of channels
required by proxy-assisted catching is less Verified using following setup :
L : 90 min. video object
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Proxy-Assisted Selective Catching
Combines Proxy-Assisted Catching and Controlled Multicast
Broadcast most frequent videos using Proxy-Assisted Catching and less frequent videos using Controlled Multicast
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Classifying “Hot” and “Cold” videos
Hot video if
Total no. of channels required using catching
Total no. of channels required using controlled multicast
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Simulation results
Simulation settings N : No. of video objects on central server λ : Request rate (Poisson's distribution) Simulates 150 hours of client requests Ki* : Broadcasting channels for “hot” video
objects Remaining channels for controlled multicast First-come-first-serve basis
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Assumptions
Sufficient proxy resources to store prefixes for all videos
Proxy server has 40GB of storage space and I/O bandwidth of 88 Mb/s
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Total no. of channels vs. arrival rate
100150
Performance of selective catching and catching same
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Waiting time vs. Server channels
460 700
36% saving in number of channels required at central server
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Waiting time vs. Server channels
Advantage of proxy-assisted selective catching does not critically depend on availability of proxy storage space
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Conclusion
Approach is proved using quite realistic simulations without any major assumptions
If the arrival rate exceeds beyond certain assumptions then the service latency will increase