The envelope definition defines the content of the first and last lines of the file/transmission (see Table 25.1).
The first or header line contains an identifier specifying that this is a message complying with a UKBTS specification, the date and time generated, the source and destination of the message, and the protocol number which identifies the relevant protocol to which the message conforms.
Source and destination identifiers for the Blood Establishments will be the ISBT 128 collection facility identification code. It is anticipated that hospital blood banks will use the identifier assigned by their local Blood Establishment.
The terminator line contains a record count indicating the total number of message lines excluding the header and terminator lines, and a standard terminator message.