Data communication is carried out between nodes each not having a global
address. In a network management system in which a first network and a
second network which have the different address systems are connected to
each other through an address translator, each of the first and second
networks has a node and a management protocol proxy; and each of the
management protocol proxies includes a management protocol proxy data
generating unit for treating, as management protocol proxy data, a
transmission source address, a transmission destination address and data
in a protocol data unit which are contained in a packet of a management
protocol sent from the associated one of the nodes, and an address
translation unit for translating the address information in the protocol
data unit contained in the management protocol proxy data sent from the
other management protocol proxy.