Vessel mounted AIS transceiver (transmit and receive) which operates using carrier-sense time-division multiple-access (CSTDMA). Class Bs transmit at 2 W and are not required to have an integrated display: Class Bs can be connected to most display systems which the received messages will be displayed in lists or overlayed on charts. Default transmit rate is normally every 30 seconds, but this can be varyed according to vessel speed or instructions from base stations. The Class B type standard requires integrated GPS and certain LED indicators. Class B equipment receives all types of AIS messages.