Date: Friday, 18 October 1985  22:20-MDT
From: covert%castor.DEC at decwrl.DEC.COM (John Covert)
To:   TELECOM at MIT-MC
Re:   S.I.T.s (Special Information Tones)

The first two tones can vary, but the last tone is always the same.
This provides a binary encoding indicating four different meanings.
 
	Tone 1		Tone 2		Tone 3
  Low: 	913.8 Hz	1370.6 Hz
  High:	985.2 Hz	1428.5 Hz	1776.7 Hz
 
Low tone is always 274 ms, High is 380 ms
 
Category: Reorder	Low  High
	  Vacant Code	High Low
	  No Circuits	High High
	  Intercept	Low  Low
 
/john