Gossip Protocol - Gossip Communication

The concept of gossip communication can be illustrated by the analogy of office workers spreading rumors. Let's say each hour the office workers congregate around the water cooler. Each employee pairs off with another, chosen at random, and shares the latest gossip. At the start of the day, Ted starts a new rumor: he comments to Sally that he believes Fred dyes his mustache. At the next meeting, Sally tells Jill, while Ted repeats the idea to Sam. After each water cooler rendezvous, the number of individuals who have heard the rumor roughly doubles (though this doesn't account for gossiping twice to the same person; perhaps Ted tries to tell his story to Mark, only to find that Mark already heard it from Jill). Computer systems typically implement this type of protocol with a form of random "peer selection": with a given frequency, each machine picks another machine at random and shares any hot rumors.

The power of gossip lies in the robust spread of information. Even if Jill had trouble understanding Sally, she will probably run into someone else soon and can learn the news that way.

Expressing these ideas in more technical terms, a gossip protocol is one that satisfies the following conditions:

• The core of the protocol involves periodic, pairwise, inter-process interactions.
• The information exchanged during these interactions is of bounded size.
• When agents interact, the state of at least one agent changes to reflect the state of the other.
• Reliable communication is not assumed.
• The frequency of the interactions is low compared to typical message latencies so that the protocol costs are negligible.
• There is some form of randomness in the peer selection. Peers might be selected from the full set of nodes or from a smaller set of neighbors.