Transcript Loopback: Exploiting Collaborative Caches for Large-Scale Streaming ,

Loopback: Exploiting
Collaborative Caches
for Large-Scale Streaming
Ewa Kusmierek, Yingfei Dong,
Member, IEEE, and David H. C. Du,
Fellow, IEEE
Outline
Abstract
Related work
Client collaboration with loopback
Loopback analytical model
Local repair mechanism enhancing
reliability
 Conclusion and future work
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Abstract(1/2)
 Two-level streaming architecture
 content delivery network(CDN) to deliver
video from central server to proxy servers.
 Proxy server delivers video with the help of
client caches.
 Design Feature
 Loopback approach
 Local repair scheme
Abstract(2/2)
 Objective
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Reduce the required network bandwidth
Reduce load of central server
Reduce cache space of a proxy
Address client failure problem
Outline
Abstract
Related work
Client collaboration with loopback
Loopback analytical model
Local repair mechanism enhancing
reliability
 Conclusion and future work
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Related work
 P2Cast:
 A session is formed by clients arriving
close in time.
 Application-level forwarding tree.
Server
peer
peer
peer
peer
peer
Related work
 CDN-P2P hybrid architecture:
 Divide data into fractions
 A Client may receive video stream from multiple
peers, A client need to cache an entire video
 Client needs to caches an entire video
server
peer
peer
peer
Outline
 Abstract
Related work
Client collaboration with loopback
Loopback analytical model
Local repair mechanism enhancing
reliability
 Conclusion and future work
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Basic assumption for client
 Each client dynamically caches a portion
of a video and storage space is limited
 Client delivers only one stream at a time
only during its own video playback and
for a short period of time after the
playback ends
 Client may fail or choose to leave while
delivering the video data to its peers.
Basic assumption for proxy
 Storage space is limited.
 Bandwidth is limited.
 The prefix of a video is cached by
proxy server.
Forwarding Ring(1/3)
 Clients arriving close to each other in
time form a forwarding ring
 First client receiving data from a proxy.
 Last client returning data to the proxy.
 First client receives the video prefix
from the proxy and the remaining
portion of a video from the central
server
Forwarding Ring(2/3)
 Next client join on time:
 Streamed to the newcomer.
 The frames that have been already
transmitted are removed from the
buffer.
 If next request arrive not in time
 Oldest frames are passed back to the
proxy and evicted from the buffer.
 The late newcomer starts a new loop.
Forwarding Ring(3/3)
 Proxy does not maintain a copy of a
frame after transmitting to a client.
 If the demand is high:
 There are few long loops containing many
clients.
 The entire video may be cached by the
clients.
 Proxy only need to forward one stream
to each loop and receive one stream
from each loop
Outline
Abstract
Related work
Client collaboration with loopback
Loopback analytical model
Local repair mechanism enhancing
reliability
 Conclusion and future work
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Loopback analytical model
 Analyze the resource usage at the
proxy and the central server load due
to a single video under a given client
arrival process.
 Notation definition:
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:buffer size at each client
:arrival time of the i’ th client.
:storage space of the proxy( 0<
<1)
Aggregate Loop Buffer Space
Data available locally
Proxy Buffer Space Utilization
Proxy I/O bandwidth usage
Central server load
Outline
Abstract
Related work
Client collaboration with loopback
Loopback analytical model
Local repair mechanism enhancing
reliability
 Conclusion and future work
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 Client failure effect:
 Loss data has to be obtained from central server,
incurring delays.
 May affect succeeding clients in a loop.
 The higher the demand, the larger the influence
of a failure on the performance
 Address this issue with redundant caching
schemes.
 significantly reduces server load
  shortens the repairing delay caused by
transmitting missing data
Complete-local and partial-local
repair
Additional loads saved by local
repairs
Outline
Abstract
Related work
Client collaboration with loopback
Loopback analytical model
Loopback performance for multiple videos
Local repair mechanism enhancing
reliability
 Conclusion and future work
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Conclusion
 Loopback mechanism for exploiting
client collaboration in a two-level
video streaming architecture.
 Improve resource usage
 Server Network bandwidth and I/O bandwidth
 Proxy Network bandwidth and I/O bandwidth
 Proxy storage space
 Analyze the effect of client failures and
developed local repair approaches
Future work
 Allow varying amount of resources
committed by each client
 Each client can specify how much disk
space can be utilized
 According to network bandwidth ,
each client can decide how many
clients he want to serve , and for
what period of time