| 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 string characters the UNA segment need not be sent. When it is sent it must
immediately precede the UNB segment and contain the six service string characters 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 then 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 character set B to
F. |