WP4 General Architecture Outline

WP4 General Architecture Outline

1. Globat Event Notification System

• Subscription to channels (opposed to content-based pub/sub systems)
• Channel Hierarchy
  • Master channel
    • Information about specific channels
    • Used to create/delete channels
  • In every channel
    • Notifications are sent via the channel to interested peers and contain metadata on package update/removal/addition, errata, anouncement of new versions etc.
      • Metdata includes "pointers" to how to get the new/updated package (either by the seeding or "completion" phases)
      • Anouncement of new version contains a "pointer" to the hdlist of the version, and the hdlist offers "ways" to get the different packages
    • A hdlist or change-log file exists, or can be easily established by the user
    • Need some mechanism for permissions (or stick to one root/leader?)
• A "fixed" channel VS. Content-based pub/system
  • Overlay structure of the peers in a channel model is more constant, and requires less overhead to maintain
  • Channel model is less flexible than the content-based model
  • The channel model has simpler and more efficient implementations

2. Feeding/Seeding (Push)

• Goal - create a large number of sources, among interested peers, for a new package or group of packages, in a fast and efficient way.
• "Hope" - application-level multicast system is superior to the ad-hoc dissemination of files using traditional P2P file sharing application.
• Basic concept - Peers are organized into one or more efficient trees and get packets from other peers in a push-like fashion.
• Possible implementations:
  • Splitstream
  • Bullet
  • Scribe
  • Bayeux

3. Completion (Pull)

• Goals
  • Enable users that participated in the feeding phase, but failed to get some blocks/packages to get closure
  • Allow a user thas "missed" the seeding phase to download packages from fellow peers (the assumption is enough sources were created using the seeding phase)
  • Allow users to get previous versions of packages & distributions (i.e. A distributed search mechanism)
• Will be implemented either by a variant of File Sharing and/or Persistent Storage (see OceanStore)