Data policy operates on the data plane in the Cisco SD-WAN overlay network and affects how data traffic is sent among Cisco SD-WAN devices in the network. The Cisco SD-WAN architecture defines two types of data policy, centralized data policy, which controls the flow of data traffic based on the IP header fields in the data packets and based on network segmentation, and localized data policy, which controls the flow of data traffic into and out of interfaces and interface queues on the devices.
Reference: https://www.cisco.com/c/en/us/td/docs/cloud-systems-management/network- automation-and-management/dna- center/tech_notes/sda_fabric_troubleshooting/b_cisco_sda_fabric_troubleshooting_guide.html

Operation Modes
There are two modes of operation for the FlexConnect AP.
Connected mode: The WLC is reachable. In this mode the FlexConnect AP has CAPWAP connectivity with its WLC.
Standalone mode: The WLC is unreachable. The FlexConnect has lost or failed to establish CAPWAP connectivity with its WLC. A WAN-link outage between a branch and its central site is a example of such a mode of operation.
FlexConnect States
A FlexConnect WLAN, depending on its configuration and network connectivity, is classified as being in one of the following defined states.
Authentication-Central/Switch-Central: This state represents a WLAN that uses a centralized authentication method such as 802.1X, VPN, or web. User traffic is sent to the WLC via CAPWAP (Central switching). This state is supported only when FlexConnect is in connected mode.
Authentication Down/Switching Down: Central switched WLANs no longer beacon or respond to probe requests when the FlexConnect AP is in standalone mode. Existing clients are disassociated. Authentication-Central/Switch-Local: This state represents a WLAN that uses centralized authentication, but user traffic is switched locally. This state is supported only when the FlexConnect AP is in connected mode.
Authentication-Down/Switch-Local: A WLAN that requires central authentication rejects new users. Existing authenticated users continue to be switched locally until session time-out if configured. The WLAN continues to beacon and respond to probes until there are no more existing users associated to the WLAN. This state occurs as a result of the AP going into standalone mode. Authentication-local/switch-local: This state represents a WLAN that uses open, static WEP, shared, or WPA2 PSK security methods. User traffic is switched locally. These are the only security methods supported locally if a FlexConnect goes into standalone mode. The WLAN continues to beacon and respond to probes. Existing users remain connected and new user associations are accepted. If the AP is in connected mode, authentication information for these security types is forwarded to the WLC.

RSSI, or "Received Signal Strength Indicator," is a measurement of how well your device can hear a signal from an access point or router. It's a value that is useful for determining if you have enough signal to get a good wireless connection.
This value is measured in decibels (dBm) from 0 (zero) to -120 (minus 120). The closer to 0 (zero) the stronger the signal is which means it's better, typically voice networks require a -65db or better signal level while a data network needs -80db or better.