On Cache Prefetching Strategies For Integrated InfostationCellular Network

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On Cache Prefetching Strategies For Integrated
Infostation-Cellular Network

• Jerry Chun-Ping Wang, Hossam Elgindy
• School of Computer Science Engineering
• University of New South Wales, Sydney, Australia
• Justin Lipman
• Intel Asia Pacific Research Development
• Shanghai, China

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Outline

• Infostation Networks
• Integrated Infostation-Cellular Network (IICN)
• Cache prefetching problems
• Our approach Longest Tree Distance Out (LTDO)
• Results
• Conclusion

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What is Infostation

• Infostation is a type of wireless network
  that combines many low cost, limited transmission
  range and high-bandwidth local wireless stations
  over an extended terrain. As mobile clients pass
  through the coverage area of an infostation, the
  information will be delivered to the clients. The
  information delivery process is aimed to be
  automatic and does not require any human
  interaction.
• Types of information an Infostation might
  provide
• - Location-dependent information
• - Non-urgent information
• - Distributive material
• - Informative material

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Features of Infostation

• Advantages
• Using combination of several discontinuous
  wireless LAN as oppose one large ubiquitous
  wireless WAN
• Relatively cheaper equipment and access cost
• Easy to setup
• High data rate access for users in transiently
  close proximity to an infostation
• Disadvantage
• Non-ubiquitous coverage
• Provides only opportunistic service
• Clients have to access information in the absence
  of a network especially in between infostations.

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Comparison between infostation and cellular
networks
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Why integrating infostation and cellular network?

• It became common to see devices to equip with
  multiple radios interfaces due to the
  commoditization of RF transceivers.
• Utilizing multiple radios in an integrated
  manner to accomplish a common task would provide
  significant benefits in terms of functionality
  and performance.
• 3G-WLAN inter-networking is also part of 3G
  system design.

P. Bahl, A. Adya, J. Padhye, and A. Wolman,
Reconsidering wireless systems with multiple
radios, ACM SIGCOMM Computer Communications
Reviews 34(5), 39-46,2004 3GPP. 3GPP system
to Wireless Local Area Network (WLAN)
Interworking Functional and architectural
definition (Release 6). 3GPP TR 23.934 V1.0.0.
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Intergrated Infostation-Cellular Model

• Information could be retrieved from two sources
  infostation and cellular networks.
• Infostation continuously broadcasts data to its
  neighborhood in one direction only.
• Cellular network provides data unicast via
  explicit requests from client.

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Intergrated Infostation-Cellular Model (cont.)

• The integration would effectively reduce the
  number of explicit requests due to broadcast
  advantage.
• It alleviates bottleneck on the server, as well
  as saving the cost from accessing information via
  expensive cellular network.

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Cache prefetching problems

• We need a cache prefetching scheme to utilize
  broadcast well.
• The caching management strategies such as LRU and
  LFU do not work well as they can not cache data
  prior to access.
• FIFO blindly caching information in advance but
  will cause some important data to be thrown out.
• PT calculates the product of access probability
  of item (P) and the time (T) that will elapse
  before that item appears on the broadcast, and
  store items with higher PT value.
• PT calculate PT value on every clock tick, and
  require to obtain information from remote server.
  

S. Acharya, S. Zdonik and M. Franklin .
"Prefetching from a Broadcast Disk ". In
Proceedings of 12th International Conference on
Data Engineering (ICDE96), page 276, 1996
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Requirements

• We need a cache pre-fetching strategy that
• utilizes broadcast by selectively caching data in
  advance.
• uses client-oriented approach
• does not require frequent calculation

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Assumptions

• Clients are browsing through a direct-access
  hierarchy of named catalogues and files from a
  remote server.
• Each catalogue contains not only the relevant
  files to the catalogue, but also the
  sub-catalogues that contains refined information.
• The file system forms a hierarchical data
  structure.
• Every client starts the access from the root of
  tree.

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Tree Distance
We define the Tree Distance (TD) as the
number of edges that is required to reach from
one item to another along the data hierarchy.
H(X) The size of set X A, B The set of
parents from the root to the selected item
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Longest Tree Distance Out (LTDO)

• LTDO evicts data item out of cache if the item
  has highest TD value.
• LTDO is only based the clients access pattern
  and does not require to obtain the knowledge of
  broadcast queue in order to calculate the value.
• It only calculates the TD value whenever the
  client is change its currently accessed item.
• Cache can remain cohesive with the information
  hierarchy, thereby utilize the broadcast channel.

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Simulation Environment

• 4 infostations locates at each corner of a 3km x
  3km terrain, and each provides a non-overlapping
  coverage.
• Each infostation has 6 clients (total of 24)
  within the neighborhood of infostation and each
  accessing information arbitrarily along the data
  hierarchy in a regular time interval.
• Infostations broadcast data in sync according to
  the broadcast sequence provided by broadcast
  sequence generator.

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Broadcast Sequence Generation

• Hierarchical Partition (HPar) is a hierarchical
  formulation of a broadcast disk which is
  derived from index tree proposed by
  Imielinski.
• Using Breadth First Search to traverse on data
  hierarchy and form a broadcast sequence.
• Data Tree will be split into two smaller
  sub-trees. The sub-trees can be recursively
  split into finer sub-trees.
• The degree of partition is defined as the number
  of recursion done on splitting the data tree.

T. Imielinski, S. Viswanathan, and B. R.
Badrinath. "Energy Efficient Indexing On Air". In
Proceedings of ACM SIGMOD Conference, pages 25--
36, 1994. Swarup Acharya, Rafael Alonso,
Michael Franklin, and Stanley Zdonik. "Broadcast
Disks Data Management for Asymmetric
Communication Environments ". In Proceedings of
ACM SIGMOD Conference, pages 199--210, 1995.
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Broadcast Sequence Generation (cont.)
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Simulation Results (FIFO)
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Simulation Results (FIFO) cont.
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Simulation Results (LTDO)
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Simulation Results (LTDO) cont.
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Conclusion

• Introduced Integrated Infostation-Cellular
  Network Model
• Infostation continously broadcast information to
  the clients in the neighborhood, while
  basestation provides unicast through explicit
  request.
• Provided Longest Treed Distance Out (LTDO)
• Evicts the data item that has longest tree
  distance.
• The simulation has shown LTDO has great
  performance improvement than using FIFO.
• Future Works
• A better broadcast scheduling should be provided
  in accordance to client/server interaction.
• Better calculation method for tree distance.

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Thank you