When a Client Node on the FieldServer goes offline the corresponding data objects on the FieldServer are also marked offline. If a client polls a virtual FieldServer node for this particular data, an offline response will be returned by the FieldServer. If the client then requests the FieldServer to identify itself, a valid response will be provided in spite of the data being offline. This results in status toggle, with the Server side Client receiving no replies to data requests and marking the Node offline and then again marking the node online after a successful identification poll, then again receiving no replies to data requests and marking the node offline and so on.
The Server Node must therefore be capable of deciding the nature of its response based on the status of relevant Client Nodes. This can be accomplished using responsible Map Descriptors (RDBC, WRBX, and WRBC). In case no acknowledgement of these functions is received, the device is identified as offline and a flag is placed at the data array offset. The virtual FieldServer can be configured using the Offline_Method option to respond to identification requests in one of the following ways:
- <! [if !supportLists] >Ignore_Clients/No Setting (default) – The kernel ignores the status of Client side Nodes and uses only the online/offline status of relevant data objects to decide on the type of response.
- <! [if !supportLists] >Any_Offline – If any relevant Client Node is offline the Server Node will respond with a node offline message as defined by the Server protocol. This option is available for selected drivers only.
- <! [if !supportLists] >All_Offline – If all relevant Client Nodes are offline the Server Node will respond with a node offline message as defined by the Server protocol. This option is available for selected drivers only.
- <! [if !supportLists] >Always_Respond – A response with data currently in the FieldServer is always sent, without considering the online/offline status of the relevant Client Nodes. This option is available for all drivers.
Offline Server Nodes are treated differently by different protocols. Some protocols will have an explicit offline response, while others will simply not respond.
If configured, the node offline response will take priority over the data offline response.