Remote station monitoring via ARP
The EAP is based on the connection-less protocols (Ethernet protocol and UDP/IP). These protocols do not return acknowledgements for messages. The TwinCAT EAP device uses the Address Resolution Protocol (ARP) for remote terminal monitoring, in order to enable the sender of an EAP telegram to detect that the receiver is no longer available. The ARP Retry Interval can be used in an EAP Publisher to configure the time frame for checking whether the receiver is still accessible. Remote terminal monitoring (Subscriber Monitoring) can only be enabled if a unicast connection is configured.
If Subscriber Monitoring is enabled, the Publisher sends an ARP Request telegram to the configured target device, based on the configured time interval. If the receiver still operates as expected, it responds with an ARP reply telegram. Otherwise there is no response. In the diagnostic variable FrameState (see Publisher), the third bit (0x0004) is set in the event of an error.
 | ARP handling The ARP handling for assigning MAC addresses to network addresses (IP addresses) is treated by the operating system (Windows). The ARP handling for assigning MAC addresses to AMS NetIDs is handled by the TwinCAT system. |