Cook over IP: Adapting TCP for cordless kitchen appliances

Cordless kitchens are the next big step in Smart Kitchens that are enabled by the Internet of Things (IoT) paradigm. The appliances in a cordless kitchen are powered by inductive power sources (PTx) that are integrated into kitchen counter-tops. The appliance and the PTx exchange control information using a near-field communication (NFC) channel. These appliances currently do not have Internet connectivity to enable smart cooking and control of the appliance from smartphones. Embedding a WiFi radio powered by batteries on the appliance is undesirable as batteries require recharging or replacement, and also increase the cost of the appliance. Therefore, we propose to connect the PTx to Internet and exploit the NFC channel for tunneling Internet traffic to the appliances. Due to the heavy magnetic fields induced by the PTx, this NFC channel has to be time-slotted, which is unique to the cordless kitchen appliances. This introduces many challenges on the communication, as the low data rates and high latencies of the NFC channel are aggravated by the slotting of the NFC channel. We focus on the TCP protocol as it is the most widely used transport protocol on the Internet. The performance of TCP is severely affected due to the time-slotted NFC channel. We identify two major problems that occur when TCP/IP is tunneled over the time-slotted NFC channel, namely spurious retransmissions of the TCP packets and packet drops at the NFC interface. Since most of the TCP/IP sessions in this environment are short, relying on TCP's natural course to adapt to long delays is not viable. To solve these, we propose a method to determine optimal TCP retransmission timeout values, and a channel sensing mechanism to avoid packet drops. In addition, we perform a detailed analysis to study the influence of parameters such as the contention window size, maximum segment size and NFC bit error rates. We implement and evaluate the solutions on a cordless kitchen testbed. We find that the proposed solutions almost completely eliminate the spurious retransmissions and packet drops. Furthermore, we achieve up to 53% lower end-to-end latency at 24 kbps in the NFC time-slotted mode.