diff --git a/docs/ARCHITECTURE.md b/docs/ARCHITECTURE.md
index 9ab2337..a8bcf73 100644
--- a/docs/ARCHITECTURE.md
+++ b/docs/ARCHITECTURE.md
@@ -190,9 +190,15 @@ subscribes to the bus and renders itself.
 
 | Path | Transport | Notes |
 |---|---|---|
-| `app-flutter` | USB (RNDIS), or WiFi | The display. Full client, richest UI, also the audio sink |
+| `app-flutter` | USB (NCM: tablet is host, Orin at `192.168.55.1`), or WiFi | The display. Full client, richest UI, also the audio sink |
 | `app-esp32` + RLCD/e-ink | WiFi, or USB/BT serial | Low-rate glanceable subset. Not in current scope |
 
+Over USB, Android sends app traffic only via its *default* network, and the
+USB link, having no internet, never becomes default while WiFi or cellular is
+up. `app-flutter` must request the Ethernet network (`TRANSPORT_ETHERNET`) and
+bind to it. The Orin's USB-C port can't charge the tablet (no USB PD), so in the
+car the link runs through a PD hub that feeds the tablet from the car charger.
+
 Displays reaching the bus over IP connect to the broker through `svc-gw`, which
 owns the boundary. For transports without IP — BT SPP, plain USB serial —
 `svc-gw` bridges serial ↔ bus rather than each device inventing its own protocol.