> > > Now of course if the application wants to be aware, it can > > > "subscribe to events" that let it know that it happened. > > > >That sounds remarkably like a "presence" service. > > > No, what it is is a socket call you make that "subscribes" do address > events on the socket. Thus when a peer adds and deletes an > address you get a "notification" message up the socket buffer > telling you that an address was added and one was deleted. Both are needed. That is, you need a way for the host IP stack to know that a peer has moved to a different locator, and you need timely notification that this has happened. This is a lot like a presence service, but it needs to operate at layer 3, and it needs to act in response to sending IP packets to the old locators (polling a presence server is either too slow or - if you do it often enough - too wasteful). And yes, you probably also need a socket call that the app can use to ask that it be notified of changes in peers' locations, because location changes can also result in changes in the level of service available to the app. though hopefully most apps won't need to use it. Keith