A transport protocol is a protocol that is responsible for actually sending messages on the network and receiving them from the network.
persistent_ports="true" Whether or not to maintain the list of recently used ports in stable storage
persistent_ports_file="/tmp/jgroups-ports.txt" The fully qualified filename of the file in which persistent ports are maintained
ports_expiry_time="30000" The time in ms after which ports are removed and can subsequently be reused
For more information read this (reincarnation section)