Observer method invoked when a contact is added to the routing table.paramcontact the added contact
Router is not longer in useparamrouter
Observer method invoked when a contact changes between a bucket entry and a replacement in the routing table.paramcontact the contact that changed location
Observer method invoked when a contact is found to be alive.paramcontact the contact now alive
Observer method invoked when a contact is found to be failing.paramcontact the contact now failing
Observer method invoked when a contact is removed from the routing table.paramcontact the removed contact