AX.25 uses a special frame for this operation, the Unnumbered Information (UI) frame. In this type of
operation, the destination address has a code word installed in it that prevents users of that specific round-table
from seeing all frames going through the shared RF medium. For example, if a group of amateurs are engaged
in a round-table discussion about packet radio, they could put “PACKET” in the destination address; they will
receive frames only from others in the same discussion. An added advantage of the use of AX.25 in this manner
is that the source of each frame is in the source address subfield; software could be written to automatically
display who is making what comments