It is sent back to a User in response to a query. User to base search on. Initialized only in constructor. The MessageHandler code walkthrough explain the function of each message handler in greater detail. The following is a pseudo code walkthrough of the Message Handlers.
User starts application.
With a completely connected graph topology this will result in redundant neighbour Addresses. In future versions a more sophisticated network topology will be assumed so the redundant data will be greatly limited. When a socket doesn't respond to an attempt to send it a message a SendException is generated. Node catches that exception and deletes the node that caused the exception from the NeighbourList. This allows a node to keep it's NeighbourList current without relying on remote nodes sending messages telling us it's disconnecting.