4.2 Technology

Figure 4.1 shows the structure of a LonWorks packet, including data fields used by each protocol layer. The protocol layers are detailed in the following sections.

Figure 4.2 LonWorks media channels (most common in bold). Reproduced by permission of © Echelon Corporation.

4.2.1 Physical Layer

The LonWorks protocol is media independent, and assumes only a physical layer that can transmit binary signals, called a channel. Specific transceivers are required for each underlying physical layer. The series of standards defines transceivers for twisted pair, link power, power line, radio frequency, optical fiber, coaxial cable, and infrared media channels (Figure 4.2, the complete list can be found at http://www.lonmark.org/spid). Most of the transceiver channels use differential Manchester encoding, where each “1” is transmitted as a polarity reversal for a full period, and each “0” is represented as two polarity reversals during a single, full period. This type of encoding ensures that there is no continuous component in the transmission (it averages to 0 regardless of the information transmitted), and that connections – particularly those using two wires – that not need to care about polarity.