Advantech EKI-6321AG User Manual page 25

There is a set of connection code for "Normal Node" to decide reconnecting access point in DC-MESH
topology:
ISP ID
"ISP ID" is a specific 32bits digitized code for one wireless network service provider.
When "Normal Node" is switching to the other Daisy Chain link, "Normal Node" will match the "ISP ID" of
the new Access Point before connection is created.
SUB ID
"ISP ID" is an assistant code of "ISP ID". Usage of "SUB ID" is same as "ISP ID".