feedtree: sharing web micronews with peer-to-peer event notification d. sandler, a. mislove, a....
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![Page 1: FeedTree: Sharing Web Micronews with Peer-to-Peer Event Notification D. Sandler, A. Mislove, A. Post, P. Druschel Presented by: Andrew Sutton](https://reader030.vdocument.in/reader030/viewer/2022032800/56649d375503460f94a107f7/html5/thumbnails/1.jpg)
FeedTree: Sharing Web Micronews with Peer-to-Peer
Event Notification
D. Sandler, A. Mislove,A. Post, P. Druschel
Presented by: Andrew Sutton
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Contributions
• Propose alternative to RSS distribution architecture
• Use peer-to-peer technology to reduce network load
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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
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RSS Distribution Network
• Readers poll content providers
• Request RSS files every ~30 minutes
• Readers can be online, requesting 24/7
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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
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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
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Related Work
• Improved Polling
• Outsourced Aggregation
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Improved Polling
• 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
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Outsourced Aggregation
• Content Providers supply RPC interface to aggregator
• User readers query central server instead of providers
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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
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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
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FeedTree Architecture
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Pastry
• Enables Peer-to-Peer networking applications– Self-organizing - nodes added, removed
dynamically– Network overlay - efficiently routes
messages in participating nodes
• Applications: Scribe, SplitStream
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Overlay Network
• Logical network built on top of actual network
• Can define virtual routes between nodes
• Common approach for P2P networks
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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
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Scribe
• Group Communication and Event Notification– Highly dynamic groups (based on topics)– Uses publish/subscribe model– Allows application-level multicast and
anycast
• Applications: FeedTree, ???
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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
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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
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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”
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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
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Publisher Delivery Tree
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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
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Implementation
• Implemented both publisher/reader software (proxies)
• Created testbed website for real distribution of RSS feeds
• No substantial experimentation
http://www.feedtree.net
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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
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Disadvantages
• Requires specialized software for publishers/subscribers
• P2P denial of service attacks– Malicious nodes may not forward events
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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
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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)
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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?
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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?
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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?