Implicit group messaging in peer-to-peer networks Daniel Cutting, 30th November 2005

Implicit group messaging November 30, 2005 Slide 2 Outline. Explicit and implicit groups P2P networks Implicit group messaging My approach Addressing Grouping Routing Evaluation

Implicit group messaging November 30, 2005 Slide 3 Explicit groups. Group “Griffin” Lois Peter Stewie Brian Group “A-Team” Homer Peter

Implicit group messaging November 30, 2005 Slide 4 Implicit groups. Implicit groups Soccer Soccer AND Argentina Australia OR Argentina (Soccer OR Football) AND Argentina

Implicit group messaging November 30, 2005 Slide 5 Explicit and implicit groups. Explicit groups: members are named Membership managed as a central list or a distributed structure (e.g. multicast group trees) Members explicitly join (individually or by a coordinator) Implicit groups: members are described E.g. “Everyone interested in soccer” Members don’t join, they just match the description

Implicit group messaging November 30, 2005 Slide 6 P2P networks. Overlay networks of hosts (“peers”) on the Internet Structured (CAN, Pastry ) : peers reside in a logical space and are connected in some ordered and consistent way Unstructured (Gnutella, KaZaA): more ad hoc P2P commonly used to swap files, but also good for: Distributed data storage, academic collaboration tools, large multiplayer games, message forums Want support for messaging groups within these networks (for searches, requests, events, etc.) Implicit groups are good for these!

Implicit group messaging November 30, 2005 Slide 7 P2P networks. Hand of God (Soccer OR Football) AND Argentina

Implicit group messaging November 30, 2005 Slide 8 Implicit group messaging. AIM: Deliver messages from any peer to any implicit group at any time in a P2P network Assumptions: Each peer describes itself with attributes (strings indicating capabilities, interests, services, …), e.g. “Soccer”, “Argentina” Implicit groups are specified as logical expressions of attributes, e.g. “(Soccer OR Football) AND Argentina” System delivers messages from a source to all peers matching the expression

Implicit group messaging November 30, 2005 Slide 9 My approach. A fully distributed, structured overlay network Peers build and maintain a logical Cartesian surface Each peer resides at a logical address on surface Each peer owns part of the surface and knows its neighbouring peers Key features Addressing: a peer’s address encodes its attributes Grouping: a group’s description encodes all possible addresses of matching peers Routing: source uses group description to reactively construct a multicast tree to all possible addresses

Implicit group messaging November 30, 2005 Slide 10 What does a surface look like?

Implicit group messaging November 30, 2005 Slide 11 But what does it mean?! Lois {Soccer, Australia} Peter {Australia} Brian {Soccer} Homer {Football, Argentina, Donuts} Stewie {Soccer, Argentina}

Implicit group messaging November 30, 2005 Slide 12 JOINing the network. New peer calculates its address Routes a JOIN request to that address from a bootstrap Peer that currently owns the address partitions its part of the surface All neighbours are informed To leave the network give your parts of the surface to your neighbours

Implicit group messaging November 30, 2005 Slide 13 Getting around on the surface. Each peer knows its neighbours When given a message with a destination address, pass it on to geometrically nearest neighbour

Implicit group messaging November 30, 2005 Slide 14 Addressing. How does a peer determine its location on the surface? Each peer has a set of attributes (its interests, say) Encode these into the address of the peer using a Bloom Filter E.g. {Soccer, Argentina}  | Map the address to a part of the surface Location on surface encodes attributes

Implicit group messaging November 30, 2005 Slide 15 Addressing. Map from an address to the surface using a quadtree decomposition Quadrants called extents E.g. {Soccer, Argentina}  Pad with 0s at end (0) = 122

Implicit group messaging November 30, 2005 Slide 16 Grouping. How do we find a group of peers given a description? E.g. all peers with attributes “Soccer AND Argentina” Convert to a Bloom Filter, but wildcards (*) replace 0s {Soccer, Argentina }  *11* | So any peer with both attributes must have (at least) the 2nd, 3rd and 5th bits set in their address The wildcards may match 1s or 0s depending on what other attributes the peer has *11*1 matches addresses 01101, 11101, 01111, 11111

Implicit group messaging November 30, 2005 Slide 17 Grouping. Need to find extents where the 2nd, 3rd and 5th bits are set {Soccer, Argentina}  *1 1* 1(*) **  00, 01, 10, 11 (extents 0, 1, 2, 3) *1  01 and 11 (1, 3) 1*  10 and 11 (2, 3) 11  just 11 (3)

Implicit group messaging November 30, 2005 Slide 18 Grouping. ORs can be treated as a set of ANDs E.g. “(Soccer OR Football) AND Argentina” Equivalent to “(Soccer AND Argentina) OR (Football AND Argentina)” {Soccer, Argentina}  *11* | {Football, Argentina}  11* | All peers with address having 2nd, 3rd and 5th OR 1st, 2nd, 4th and 5th bits set are part of this group

Implicit group messaging November 30, 2005 Slide 19 Grouping. {Soccer, Argentina}  *1 1* 1(*) {Football, Argentina}  11 *1 1(*) **  00, 01, 10, 11 (extents 0, 1, 2, 3) *1  01 and 11 (1, 3) 1*  10 and 11 (2, 3) 11  just 11 (3)

Implicit group messaging November 30, 2005 Slide 20 Routing. A peer wants to send a message to an implicit group Creates a message: “Got any Hand of God photos?” Specifies an appropriate implicit group: “Soccer AND Argentina” Chooses the best neighbour(s) to forward the message Knows extents yet to be visited (everything initially) Intersects these with extents matching group description Clusters what’s left and sends a message towards each cluster

Implicit group messaging November 30, 2005 Slide 21 Routing. If many targets in same direction, only route one copy: i.e. cluster based on their direction Message splits as it gets closer to clusters since relative angles increase Clustering threshold angle can be variable Guarantees delivery

Implicit group messaging November 30, 2005 Slide 22 Evaluation. Simulation OMNeT++ implementation simulating campus- and world-scale physical networks Thousands of peers In progress Compare to alternative models IP multicast flooding (optimised physical routing, but all peers receive all messages) Centralised server (unfair to some peers/links but only member peers receive messages)

Implicit group messaging November 30, 2005 Slide 23 Evaluation. Metrics Normalised overall network traffic for messaging Peer fairness (variance of computation and storage) Network link fairness (variance of link stress) Expected results Flood should have good peer and link fairness, poor total traffic for small implicit groups Centralised should have poor peer and link fairness, good total traffic for all groups My approach should have good peer and link fairness, and good total traffic for small groups, poor for large

Implicit group messaging November 30, 2005 Slide 24 Evaluation. Peer fairness Unicast ROUTE cost Evaluation of basic features Peer storage fairness Average cost of unicast routing between two random addresses

Implicit group messaging November 30, 2005 Slide 25 Questions?

Implicit group messaging November 30, 2005 Slide 26 Ancillary slides.

Implicit group messaging November 30, 2005 Slide 27 Related work. Explicit group systems IP multicast, Usenet (consumers explicit join channels) (publisher lists recipients by name) SCRIBE (on Pastry), CAN Multicast, Bayeux (on Tapestry) Implicit group systems Khambatti et al: interest-based communities (but don’t support arbitrary cross-cutting groups) Interest management (virtual environment updates) Content-based publish/subscribe (but different semantics)

Implicit group messaging November 30, 2005 Slide 28 Content-based publish/subscribe. Conceptually similar: messages are delivered to implicit groups based on a match at time of publication Pub/sub: consumers select the type of message they receive. Implicit group messaging: publishers select type of consumer of message Converse semantics lead to differing expressiveness Pub/sub good for consumers who need to be notified of specific types of events from any publisher: e.g. GUI components Implicit group messaging good for publishers who need to reach specific types of consumer: e.g. distributed search engines

Implicit group messaging November 30, 2005 Slide 29 Future work. Very important to get physical network simulations running Testing with various attribute distributions, higher dimensional surfaces Random shortcuts through the surface to reduce routing cost (can be inserted when peers JOIN) Prefixing addresses with bits that place peers on surface with some approximation of underlying network may improve physical network usage

Implicit group messaging November 30, 2005 Slide 30 Attribute distribution. Uniform attribute distributionZipf attribute distribution {Soccer, Argentina, Sport} {Rugby, Australia, Sport} Peers with popular attributes Peers with unpopular attributes {Soccer, Argentina, Beer} {Football, Argentina}

Implicit group messaging November 30, 2005 Slide 31 Research plan. Technical Report awaiting Smart Internet Technology CRC approval Short Letter expressing basic concepts in next week Journal paper with network results by end of year Conference paper with future work early next year Complete around July

Implicit group messaging November 30, 2005 Slide 32 P2P networks. Messaging in P2P networks is often many-to-many E.g. any peer can initiate a multicast query to search for files or services Typically handled by flooding (Gnutella), superpeer registries (KaZaA), plus many other shortcuts. Some structured networks have multicast capabilities Peers can subscribe to multicast channels and receive all messages sent to that channel Need messaging between peers for: Storing/retrieving data or files Searching for particular data Searching for particular kinds of peers

Implicit group messaging November 30, 2005 Slide 33 P2P networks. P2P needs multicast (for searches, requests, events) Allows a peer to send a message to a group of recipients Often will know names of recipients, e.g. when some peers have explicitly requested notification of an event However, there are times when it won’t, e.g. searching for peers matching some criteria Often just flood the network, but may be more targeted Difference is the way multicast groups are defined: explicitly or implicitly

Implicit group messaging November 30, 2005 Slide 34 Implicit group messaging. In an ideal system: All implicit group members should receive messages Non-members shouldn’t receive them Dynamic membership should be supported Minimal total network load Fairness across peers/network links