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


• 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


• Retrieves and processes data from the feed URI

• Automatically downloads new entries


• 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



• Enhancement of 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


• 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


• Subscribed channel• Public channel


• 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.


• False positive– Possible

• False negative– Impossible!


• Data Structure– Distinct identifiers– Meta data– Internal structure• Public cache or subscribed channel• Request list for solicitation decision• Download status


• Protocol design– Receiver-driven– State machine– First state– Second state– Unbeknownst to its user(public cache)

outline


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


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?

Documents

Wireless Ad Hoc Podcasting