.PS
 Lpd: box "lpd"
 Filter: box dashed "Filter" with .w at Lpd.e + (.5,0) ;
 Printer: box "Printer" with .w at Filter.e + (1.5,0) ;
 arrow <-> from Lpd.e to Filter.w;
 arrow <-> from Filter.e to Printer.w;
 m = (Filter.e.x + Printer.w.x)/2;
 "/dev/tty00" at (m,Filter.e.y+.125)
 "\fBRead Write\fP" at (m,Filter.e.y-.125)
.PE
