I. Introduction
With the rapid development of the information technology and the CNC technology, the network management of the NC industry has become a necessity [1]. Some famous NC machine and system manufacturers in overseas, such as Mazak and Okuma in Japan, Siemens in German, etc. have realized the network monitor, diagnose and management with integrated network communication in NC system. That reflected the tendency of NC machine tool to the network direction. At the present, most of NC machines at home use the traditional closed NC system, such as the FANUC, MITSUBISHI, Siemens, etc. That kind of system, which transmits by common RS232, RS422 or RS485, is unfavorable to extend the network. So it's indispensable to append network function communication outside the NC system to put into effect network management of NC machines.