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The service string advice shall begin with the upper case characters UNA immediately followed by six characters in the order shown below. The same character shall not be used in more than one position of the UNA. This segment is used to inform the receiver of the interchange that a set of service string characters which are different to the default characters are being used. When using the default set of service characters, the UNA segment need not be sent. If it is sent, it must immediately precede the UNB segment and contain the four service string characters (positions UNA1, UNA2, UNA4 and UNA6) selected by the interchange sender. Regardless of whether or not all of the service string characters are being changed every data element within this segment must be filled, (i.e., if some default values are being used with user defined ones, both the default and user defined values must be specified). When expressing the service string characters in the UNA segment, it is not necessary to include any element separators. The use of the UNA segment is required when using a character set other than level A. UNA:+.? ' |