The CSD mail system

In principle, the CSD exchanges safety messages with other safety computers, which may be CSDs or other types of computers (the latter must know the characteristics of encoding exchanged messages). 

The CSD communicates with the outside world through physical links. A physical connection can support multiple logical paths within the meaning of the CSD. Each VL is protected by a safety coding. 

The CSD has several safety protocols. As a standard, there is a double dating protocol with data protection through SACEM encoding. The CSD also offers the ERTMS Euroradio protocols with double dating and protection of data by a 

All calculations are performed modulo the key code (large number) and where  

The safety code used for safety input/output messages is a maximum 64-bit safety code defined by the CSD user. However, as a standard, the CSD includes the SACEM code and the Euroradio ERTMS code. 

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