Wireless Ad Hoc Podcasting
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Transcript of Wireless Ad Hoc Podcasting
Wireless Ad Hoc Podcasting
Ad hoc • ad hoc network typically refers to a system of
network requiring little or no planning• a decentralized type of wireless network• The network is ad hoc because it does not rely
on a preexisting infrastructure
Wireless Ad Hoc Podcasting
• Podcasting used for media content• But inflexible• Based on Delay-Tolerant Network
outline
• Podcasting in the Internet• Delay-tolerant network• Wireless Ad Hoc Podcasting• Solicitation Strategies• Evaluation and simulation• Conclusion and comment
Podcasting• Podcasting: dissemination of streaming
contents over the Internet.• Playback off line.
Podcasting in the Internet
• Fairly simple• Channel to define a feed and make it
accessible on a web server• Feed is an XML file, which contains a list of
entries.• Subscribe to podcast channel by entering feed
URI into Podcatcher
Podcasting in the Internet
• Retrieves and processes data from the feed URI
• Automatically downloads new entries
Podcasting in the Internet
• Atom Syndication Protocol• Based on XML
outline
• Podcasting in the Internet• Delay-Tolerant Network• Wireless Ad Hoc Podcasting• Solicitation Strategies• Evaluation and simulation• Conclusion and comment
Delay-Tolerant Network
• Loosely connected network for asynchronous communication
• Intermittent connectivity
Delay-Tolerant Network
• Every node scans periodically the network neighborhood
• Nodes associate pair wise• IEEE 802.11, Bluetooth• Receiver-driven, No flooding
outline
• Podcasting in the Internet• Delay-Tolerant Network• Wireless Ad Hoc Podcasting• Solicitation Strategies• Evaluation and simulation• Conclusion and comment
Wireless Ad Hoc Podcasting
• Enhancement of podcasting
Wireless Ad Hoc Podcasting
• No means to search for podcast channels• Feed channel should be known priori• Enhancement: discovery channel• List of the feed channel, which may be empty
Wireless Ad Hoc Podcasting
• Entries must update constantly to reflect the latest status
• Entries will reach a node in arbitrary order• Atomic unit• Feed channel is composed of a mixture of
entries of music, news items, weather updates ,etc
Wireless Ad Hoc Podcasting
• Subscribed channel• Public channel
Wireless Ad Hoc Podcasting
• Request for contents:– Any content– Feed channel– Entry– Feed channel + entry• Time• Uniqueness : matches any entry not in a provided list of
entry ID’s.
Wireless Ad Hoc Podcasting
• False positive– Possible
• False negative– Impossible!
Wireless Ad Hoc Podcasting
• Data Structure– Distinct identifiers– Meta data– Internal structure• Public cache or subscribed channel• Request list for solicitation decision• Download status
Wireless Ad Hoc Podcasting
• Protocol design– Receiver-driven– State machine– First state– Second state– Unbeknownst to its user(public cache)
outline
• Podcasting in the Internet• Delay-Tolerant Network• Wireless Ad Hoc Podcasting• Solicitation Strategies• Evaluation and simulation• Conclusion and comment
Solicitation Strategies
• An open question : how to solicit to satisfy the future request.
Solicitation Strategies
• Most solicited• Least solicited• Uniform• Inverse proportional• No caching
Most solicited
• Increase the probability in a popular feed• history-based ranking• Request list of locality
Least solicited
• Opposite goal against most solicted• May waste resources•
Inverse proportional
• Mitigate the waste of unpopular cache• Inverse proportional to its popularity
Uniform and no caching
• Feed channel are treated equally and requested randomly
• No caching is used for benchmark
outline
• Podcasting in the Internet• Delay-Tolerant Network• Wireless Ad Hoc Podcasting• Solicitation Strategies• Evaluation and simulation• Conclusion and comment
Network and simulation model
• Two nodes can communicate with if distance is smaller than a threshold value
• No collision and interference• Random waypoint mobility model
Scenario Setting
• Scenario• Radio range 10 m• Moving speed 1 m/s• Rate of radio devices 1 Mb/s• Entry size 250 KB• Square 300 m X 300 m• Popularity
Performance metrics
• Freshness
• Overall and per channel average freshness• Max-min fairness
Result
• 50 nodes and 7 different channels.• varying
Result
• Uneven popularity for ,a larger value increases the probability that unpopular channels are solicited
Result
Result
• Varying Publishing rate
Result
• Varying Publishing rate
Result
outline
• Podcasting in the Internet• Delay-tolerant network• Wireless Ad Hoc Podcasting• Solicitation Strategies• Evaluation and simulation• Conclusion and comment
Conclusion and comments
• The best overall performance is uniform strategy.
• Security problem• Based on Bluetooth?• Useful in sparse district?