1. FeedTree: Sharing Web Micronews with Peer-to-Peer Event Notification D. Sandler, A. Mislove, A. Post, P. Druschel Presented by: Andrew Sutton

2. Contributions Propose alternative to RSS distribution architecture Use peer-to-peer technology to reduce network load

3. RSS Distribution RSS (Real Simple Syndication) - XML format for publishing micronews Feed - a source of RSS items Content Provider - responsible for publishing RSS feeds Reader/Aggregator - user agent responsible for RSS acquisition and display

4. RSS Distribution Network Readers poll content providers Request RSS files every ~30 minutes Readers can be online, requesting 24/7

5. Problems with Distribution Polling - Requests occur on schedule Superfluity - Full response per request Stickiness - RSS traffic persists even if web traffic subsides 24 Hour Traffic - requests occur all day long

6. Network Load Example Updates occur every 30 minutes Slashdot –Subscribers: > 17,000 –RSS file size: ~15KB –~11.6GB/Day of RSS data Difficult to measure accurately No reliable statistics

7. Related Work Improved Polling Outsourced Aggregation

8. Improved Polling –Restrict reader polling via RSS –Use HTTP caching to reduce superfluous responses –Use compress to reduce response size Delta Encoding –Only transmit what’s changed [RFC 3229] –Seemingly ideal for RSS

9. Outsourced Aggregation Content Providers supply RPC interface to aggregator User readers query central server instead of providers

10. Outsourcing Problems Central aggregator allows –Single point of failure for readers –Censorship of original content –Modification of original content (i.e., ads) May not be reliable or trustworthy

11. FeedTree Eliminate network/provider load Uses peer-to-peer subscription Use hybrid push/pull mechanism for timely distribution/update of micronews Signed documents to enable trust

12. FeedTree Architecture

13. Pastry Enables Peer-to-Peer networking applications – Self-organizing - nodes added, removed dynamically –Network overlay - efficiently routes messages in participating nodes Applications: Scribe, SplitStream

14. Overlay Network Logical network built on top of actual network Can define virtual routes between nodes Common approach for P2P networks

15. Pastry Network Based on a circular namespace of node id’s (not tree-oriented) Routing –Shortest-path based on routing –Non-receivers forward message to next- closest (proximity) node –Routes messages in O(logn) time

16. Scribe Group Communication and Event Notification –Highly dynamic groups (based on topics) –Uses publish/subscribe model –Allows application-level multicast and anycast Applications: FeedTree, ???

17. Scribe Multicast Subscribing to a topic –Subscriber knows publisher’s node id –Sends “subscribe” message –Forwarding nodes become parents in the multi- cast tree (keeps track of children) Notification of event –Events are multicast to all children of publisher, forwarders One multicast tree per topic

18. FeedTree Distribution Subscription –Readers subscribe to a feed (i.e., Scribe topic) Publication –Each item is given timestamp, sequence id –Document is signed with publishers private key

19. FeedTree Delivery Bootstrap Delivery –Signed RSS document is multicast to overlay network –Essentially, a combined subscribe/request operation Incremental Delivery –Only new items are multicast –If no changes, multicast a “heartbeat”

20. Missed Deliveries If reader is missing sequence numbers –Query parent for missing items –Nodes must buffer last n items to make re- delivery more efficient –If items still missing, query publisher

21. Publisher Delivery Tree

22. Network Overhead Assume an RSS feed generating 4KB/hour Interior node in tree with 16 children forwards < 20B/sec However… –Unknown how this scales for large providers, large readers

23. Implementation Implemented both publisher/reader software (proxies) Created testbed website for real distribution of RSS feeds No substantial experimentation http://www.feedtree.net

24. Advantages/Disadvantages Benefits - lower cost of delivering micronews –(Significantly) reduced provider load –No fear of being RSS feeds being “slashdotted” Differentiated services - different feeds for headlines/full news

25. Disadvantages Requires specialized software for publishers/subscribers P2P denial of service attacks –Malicious nodes may not forward events

26. Conclusions End users receive better service than currently possible Foresee new services based on RSS –Storing every single RSS item published on the internet –Anonymous feeds using anonymizing p2p routing algorithms –Cooperative multicast to distribute realtime media

27. Evaluation Good –Appears to be well-reasoned idea –Developed software to test hypothesis –Good workshop paper What’s needed for research –More detailed description of protocol –Substantiate claims about performance (i.e., experiment)

28. Questions 1.List four problems with the current RSS feed distribution model. 2.Which two of these four problems have the largest impact on network load?

29. Questions 3.How long does it take Pastry to route a message if there are n nodes in the network? 4.Suppose Slashdot has 50,000 RSS subscribers through FeedTree. What is the approximate depth of the multicast tree for the Slashdot topic?

30. Questions 5.Assume that there are 100,000 FeedTree topics on a Pastry network that all update at 4KB/Hour. An interior node with 16 children will send 20B/sec. Suppose an interior node participates in all feeds. What is the expected output (in B/sec) of this node?