Disclosed is a vehicle-tire chock having a light-emitting portion that emits light to make the vehicle-tire chock visible outside the vehicle. The set of one or more prisms are positioned to retroreflect the optical beam that passes approximately tangent to the rotatable wheel to cause a delay or phase shift to the beam as the rotatable wheel rotates. The ASP system dispatches the messages by retrieving the requests from the request store, generating messages for the requests, and sending the generated messages at a requestor-specific message dispatch rate. Assemblies include hardened connectors such as plugs andor receptacles suitable for outdoor plant applications attached to one or more ends of the fiber optic cables for plug and play connectivity. Also disclosed are an antenna design which may be used with the access points to improve reception, and a TDMA timeslot rotation method for avoiding lockstep interference between access points that operate on the same channel. The programming method includes maintaining a ratio of a resistance of the PCM in the higher resistance state to a resistance of the PCM in the lower resistance state constant or substantially constant independent of an ambient temperature.