INT 6F - 10-NET - CHAT
        AH = 0Ah
        DS:BX -> control parameters (see below)
        DS:DX -> chat message (see below)

Format of control parameters:
Offset  Size    Description
 00h  8 BYTEs   sender ID, defaults to node's userID if nulls
 08h  8 BYTEs   destination user ID, 'EVERYONE' may be used
 10h 12 BYTEs   destination node ID

Format of chat message:
Offset  Size    Description
 00h    WORD    length+2 of following text
 02h  N BYTEs   text, max 101 bytes