Library /sys$common/syshlp/ncphelp.hlb SET, LINE, ECHO DATA hex byte  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 Applies only to FDDI lines.  Specifies the byte consisting of two
 hexadecimal digits used as data in an echo request frame.  The size of
 the frame is determined by the ECHO LENGTH parater.  The frame is sent
 to the address specified by the ECHO TARGET parameter.

 Hex_byte must be a string of exactly two hexadecimal digits.  The
 default ECHO DATA is 55.  ECHO DATA can be set in the volatile
 database, but it cannot be defined in the permanent database.