Manufacturing equipment should be integrated to construct a computer integrated manufacturing (CIM) environment, but several economical and technological difficulties may surface when heterogeneous systems are integrated into each other. Manufacturing message specification (MMS) can be effective in such case, but the problem is that MMS-related products are comparatively expensive and most existing manufacturing equipment does not support MMS. This study focused on developing a gateway suitable to a non-MMS-compatible CNC machine-tool, and on implementing an open system interconnection (OSI) upper layer on TCP/IP. The development system was applied to a cell controller by means of heterogeneous equipment under the CIM environment and to evaluate its interoperability and portability.