Protocol which uses InetAddress.isReachable() to check whether a given host
is up or not, taking 1 argument; the host name of the host to be pinged.
Note that this protocol only works with a JDK version >= 5 ! The implementation
of this may or may not use ICMP ! An alternative is to create a TCP
connection to port 7 (echo service) and see whether it works ! This is
done in JDK 5, so unless an echo service is configured to run, this
An event was received from the layer below. Usually the current layer will want to examine
the event type and - depending on its type - perform some computation
(e.g. removing headers from a MSG event type, or updating the internal membership list
when receiving a VIEW_CHANGE event).
Finally the event is either a) discarded, or b) an event is sent down
the stack using down_prot.down() or c) the event (or another event) is sent up
the stack using up_prot.up().