Supplemented the preserveAPMode description

mkdocs/advancedusage.md

@@ -462,6 +462,10 @@ Certain communication protocols applicable to the ESP module require that the Wi
 
 [*AutoConnectConfig::preserveAPMode*](apiconfig.md#preserveAPMode) setting maintains WiFi-AP mode without disabling SoftAP inside [*AutoConnect::begin*](api.md#begin). The Sketch can utilize the WiFi connection via AutoConnect with ESP-MESH and ESP-NOW protocol by enabling this option.
 
+The following diagram quoted from the [ESP-MESH documentation](https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-guides/mesh.html#mesh-building-a-network) that illustrates the typical topology.  The module located at the Root Node bridges between the mesh network and the router by an application that handles two protocols, TCP/IP and ESP-MESH. Its SoftAP communicates with the internal mesh network as an interface of the mesh layer. On the other hand, STA performs station communication of the WiFi router as an interface of the TCP/IP layer. AutoConnect allows assists the connection between the router and the STA of the Root Node using [*AutoConnectConfig::preserveAPMode*](apiconfig.md#preserveapmode) and starting the SoftAP via Sketch separately.
+
+<img src="https://docs.espressif.com/projects/esp-idf/en/latest/esp32/_images/mesh-bidirectional-data-stream.png">
+
 ### <i class="fa fa-caret-right"></i> Make SSID of SoftAP unique
 
 You can change SoftAP's SSID and password programmatically when the captive portal starts up. By using chip specific ID of esp8266/esp32 you can make SSID of SoftAP unique. SSID and password for SoftAP is [*AutoConnectConfig::apid*](apiconfig.md#apid) and [*AutoConnectConfig::psk*](apiconfig.md#psk).