4. Traffic Pattern
Depending on the design philosophy of the home network, wall switches
may be configured to directly control individual lamps or
alternatively, all wall switches send control commands to a central
lighting control computer, which again sends out control commands to
relevant devices.
In a distributed system, the traffic tends to be multipoint-to-
multipoint. In a centralized system, it is a mix of multipoint-to-
point and point-to-multipoint.
Wall switches only generate traffic when activated, which typically
happens from one to ten times per hour.
Remote controls have a similar transmit pattern to wall switches but
may be activated more frequently in some deployments.
Temperature/air and pressure/rain sensors send frames when queried by
the user or can be preconfigured to send measurements at fixed
intervals (typically minutes). Motion sensors typically send a frame
when motion is first detected and another frame when an idle period
with no movement has elapsed. The highest transmission frequency
depends on the idle period used in the sensor. Sometimes, a timer
will trigger a frame transmission when an extended period without
status change has elapsed.
All frames sent in the above examples are quite short, typically less
than five bytes of payload. Lost frames and interference from other
transmitters may lead to retransmissions. In all cases,
acknowledgment frames with a size of a few bytes are used.