A message can be repeated, but not in that short time of a few seconds.
Pagers may ignore messages if they are received again. The user may
repeat the message, but not the transceiver.
To allow all 128 ASCII characters, a null-terminated string cannot be
used. Instead a length is used to define string length, to allow
null-character in that the message string.
The print function in frame.c is improved and used to present the
string.
