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Figure 3. Reference layout of the virtual factory

M-Service M ASSOCIATED.request

TCP OPEN, SEND

M ASSOCIATED.indication M ASSOCIATED.response

OPEN, RECEIVE SEND, CLOSE

M ASSOCIATED.confirm M RELEASE.request M RELEASE.indication M RELEASE.response M RELEASE.confirm M DATA.request M DATA.indication M U ABORT.request M U ABORT.indication M U ABORT.response

RECEIVE, CLOSE SEND RECEIVE SEND, CLOSE RECEIVE, CLOSE SEND RECEIVE ABORT TCP error signal TCP error signal

Table 1. Mapping Functions between the M-services and the TCP functions

Encoding and decoding can be used for converting DCB to PDU directly. The encoding and the decoding rule are based on abstract syntax notation 1 (ASN.1) [25][26]. The protocol data unit (PDU) is then forwarded to the TCP layer. Table 1 presents the mapping relations between M-services and the TCP functions in the MOTIP implementation [14].

The protocol stack of MOTIP using N578 rule is shown in Fig. 4. Once an MMS function is requested at the MMS client side, the synchronous service or the asynchronous service can be used for communication. Using the synchronous service, the MMS client receives a confirmation through a response from the MMS server. In the asynchronous service, the functions can be executed according to a received event through the response of MMS server. Most of implemented MMS services are executed by synchronous mode in the developed system.

3

Virtual

Factory Communication System

The developed virtual factory communication system was implemented with the Microsoft Visual C++ and OpenGL library [27]. The virtual factory is embodied by integrating each virtual real machine (VRM), the MMS-CS program, and the MOTIP programs. Each VRMs can be communicated with through the developed MMS-CS program based on the SNU MMS library [23].

The MOTIP central server program (see Fig. 5) can be located in a control room of a factory plant. The MOTIP cental server can monitor and command the MMS services to the networked manufacturing machines.

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