setting the maximum speed to zero will force the train to stop. The gradient profile may have a variable length based on the contained pairs of section length (scalar and number in the metric system) and section gradient (uphill/downhill flag and a number in %). Similarly the international static speed profile is given in a variable count of section parts with each part denoting the section length (number in meters - the scale is only given once at the start of the packet for all sections), the maximum speed (number * 5 km/h - allowed numbers are 0-120 i.e. some spare values are left over) and a flag if the speed restriction applies to the front or rear end of the train (possibly allowing for a delay). The trailer packet only contains its packet id with no parameters where 255 equals the state of all bits set in the 8-bit packet id field (11111111). Manufacture The history of ETCS has seen the formation of UNISIG (Union of Signalling Industry) in 1998 to promote the development of the system. The founding members were Alstom, Ansaldo, Bombardier, Invensys, Siemens and Thales. The group has ensured that Eurobalises may be made by several different companies; while the balises may vary in the details, they are manufactured to meet the same standards. The principal manufacturers of Eurobalises belong to a group of seven firms (Alstom, Ansaldo STS, Bombardier, Invensys, Siemens, Sigma-Digitek, Thales) within the UNIFE federation of railway suppliers. This group cooperated in developing the specifications for Eurobalises. Specifications for Eurobalises are governed by the European Railway Agency. Usage Eurobalises are not only used in the ETCS/ERTMS train protection system. There are alternative implementations that pick up on the telegram structure to encode only some packet types and adding additional specific information. ETCS trains may decode the telegrams possibly translating them like any other Class-B signalling information. It is also possible that a balise transmits telegrams for different systems allowing for a transitional phase from one variant to another as typically used when switching from a national train protection system to ETCS. The following automatic train protection systems are based on Eurobalises: ETCS – the European-wide train protection system Chinese Train Control System versions CTCS-2 and CTCS-3, used on high speed rail lines in China – a variant of the earlier Swiss Integra-Signum train protection system – a variant of the earlier Swiss ZUB