This attribute specifies the payload of each frame. The value
specified is in hexadecimal, where every two digits represent a byte.
A maximum of 24 digits (12 bytes) may be set, after which the
pattern will repeat in the payload (depending on repeatPattern
attribute).
NOTE: If a RFC 1490 header is specified, via the 1490Header
attribute, the specified pattern will begin following the header (i.e.
at the 9th byte in the payload).