To overcome these limitations some years ago a UIC working group developed a new version of 918 messages in XML syntax. This obviously makes 918 messages complex information items whose processing must be done in assembler-like languages, requiring skilled experts. Therefore each message must include a so-called "topographic label" indicating which elements are present. They are bit-oriented, in other words each bit has a specific meaning, and only relevant bits are included in the message. Since transmission lines at that time had limited capacity, the 918 messages were designed to minimise their length. The International Union of Railways (UIC) standardised such interconnection by defining a set of messages and procedures described in the 918 protocol. EUROPEAN railways started to introduce electronic passenger reservation systems in the 1960s, and this immediately gave rise to the need for online interconnection to each other to allow customers in one country to book services on trains operated in other countries.
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