  Separation of control and data planes (SCDP) is a desirable paradigm for
low-power multi-hop wireless networks requiring high network performance and
manageability. Existing SCDP networks generally adopt an in-band control plane
scheme in that the control-plane messages are delivered by their data-plane
networks. The physical coupling of the two planes may lead to undesirable
consequences. To advance the network architecture design, we propose to
leverage on the long-range communication capability of the increasingly
available low-power wide-area network (LPWAN) radios to form one-hop
out-of-band control planes. We choose LoRaWAN, an open, inexpensive, and ISM
band based LPWAN radio to prototype our out-of-band control plane called
LoRaCP. Several characteristics of LoRaWAN such as downlink-uplink asymmetry
and primitive ALOHA media access control (MAC) present challenges to achieving
reliability and efficiency. To address these challenges, we design a TDMA-based
multi-channel MAC featuring an urgent channel and negative acknowledgment. On a
testbed of 16 nodes, we demonstrate applying LoRaCP to physically separate the
control-plane network of the Collection Tree Protocol (CTP) from its
ZigBee-based data-plane network. Extensive experiments show that LoRaCP
increases CTP's packet delivery ratio from 65% to 80% in the presence of
external interference, while consuming a per-node average radio power of 2.97mW
only.
