Mobile-to-IoT Connection Topology: Direct vs Cloud vs Hybrid (2D)

Connection Mode

Direct BLE active

Scenario

Device distance from phone 4 m

Command rate 1.0 /s

Cloud network quality (loss) 3%

Live Telemetry — active mode

Round-trip latency

— ms

Delivery success

100%

Commands sent

Commands lost

All three topologies — live

Direct— msUP

Cloud— msUP

Hybrid— msUP

How it works

A mobile app can reach an IoT device three ways: Direct (App → Device over Bluetooth Low Energy), Cloud-based (App → Cloud → Device), and Hybrid — pick whichever is currently viable, preferring the faster direct link.

Direct BLE uses a cubic delivery-probability curve and a hard practical range cutoff:

P_deliver(d) = clamp(1 − (d / R_ble)^3, 0.02, 0.99)   for d ≤ R_ble
latency(d)   = 20 + 1.5·d + jitter(0..10) ms          for d ≤ R_ble
d > R_ble  →  link reports OUT OF RANGE (hard fail)

where R_ble = 12 m. Latency stays low (~20–70 ms) but delivery collapses fast as distance approaches R_ble, and the link is unusable past it — the classic BLE cliff.

Cloud relay latency is the sum of two independent network hops plus broker processing, distance-independent because the phone always reaches its own gateway/WiFi first, and it fails completely during a simulated outage:

RTT_cloud = (uplink 35–60ms) + (broker 8–18ms) + (downlink 30–55ms)
P_deliver = 1 − loss_rate           (network-quality slider)
outage=ON → P_deliver = 0, latency = ∞ (single point of failure)

Auto Hybrid re-evaluates every command: it picks Direct whenever distance is safely inside BLE range (d < 0.8·R_ble) regardless of cloud state, and falls back to Cloud only once out of range. That means Hybrid's measured latency tracks Direct's curve while in range — including surviving a cloud outage — and tracks Cloud's curve once out of range.

Drag the IoT device (or the distance slider) past ~10 m and watch Direct's delivery success fall off a cliff while Cloud stays flat; toggle the cloud outage while the device is close and Direct/Hybrid keep working while pure Cloud goes dark. The chart below sweeps distance 0–40 m and plots all three latency curves at once.

Phone (mobile app) IoT device — drag me Cloud relay