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 , 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

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?