| 摘要 |
<p>An interface allows for the transfer of real time control data with guaranteed delivery times between devices on a general purpose network and an industrial control system. A proxy server takes the role of a TCP/IP router and is configured to control the rate at which messages are forwarded from the nonreal time to the real time portion of the network, keeping the loading of the real time portion stable regardless of the external non-real time communication demand. Real time data is preconfigured and exchanged in a regular sequence, with the cyclic update period known. The length of any communication message necessary to transmit this information, plus any sequencing and acknowledgment overhead, is calculated in advance and aggregated. Each device with authority to transmit on the shared medium is given a time budget, calculated so that the total transmission quantity in unit time is deliberately limited to some fraction of the maximum transmission capability of the network. All communications from devices whose traffic loadings cannot be so controlled are arranged to pass through the proxy device in order to gain access to the deterministic network, and the proxy enforces the budget limits by introducing deliberate delays to the request messages if necessary.</p> |
