1042 Answer Supervision With A Line Side Interface

Answer Supervision is an electrical signal passed back to the calling end
of a switched telephone connection indicating that the called line has gone
off hook.  This signal can be used by terminal equipment (PBX, pay telephone,
call diverter, etc.) connected to the calling line to determine that the call 
has entered the talking state and that charging may commence. Previously 
this signal was available on trunks, not on lines.

The Answer Supervision signal consists of a reversal of the telephone line
bias voltage, the ring normally being more negative than the tip.  At the
time of answer or shortly thereafter, tip and ring are interchanged by the
switching machine, so that the tip is now more negative than the ring.  This
reversal persists at least until the called line goes on hook, and possibly
until the calling line goes on hook.  All of the other electrical
characteristics of a line equipped for answer supervision are identical to
those of a normal line.

Generic Name of ONA Service
	Product Name						BSE or CNS
===========================================================================
Answer Supervision With A Line Side Interface	
	AM - Answer Supervision With Line Side Interface	BSE
       	BA - Answer Supervision with a Line Side Interface	BSE 
	PB - Answer Supervision (Line Side)			BSE 
	USW - Answer Supervision (Line Side)			BSE

FEATURE OPERATION:
Answer Supervision is a service most useful to a "device" like a PBX or
"smart" pay telephone.  (This does not preclude its use on a line directly
connected to a telephone set, although the battery reversal may make the
set's DTMF pad inoperative during the talking state of the call.)

1. The "device" (PBX, pay telephone, etc.) goes off-hook and dials a call in
   the normal way.

2. After dialing is completed, the call is switched through the network over
   the usual array of network components, which may include tandem trunks, 
   tandem switches, Interexchange Carriers, and finally, a terminating 
   local switch.

3. When the called party answers, the terminating office changes the supervisory
   state of the incoming trunk to off-hook from on-hook.

4. This state change is passed back toward the originating local office by
   each intervening office and trunk.

5. The originating local office uses this state change to note the time of
   answer for billing purposes.  It also causes the line circuit of the line
   (equipped for Answer Supervision) to reverse the polarity of the battery 
   feed toward the "device" that placed the call.

6. When the called party hangs up, the state change, off-hook to on-hook, is
   transmitted back to the originating local office.  Depending on its
   software realization of the feature, the originating local switch may or
   may not pass this signal to the "device" by changing the battery polarity
   back to normal.  In either case the originating local switch begins
   "calling party hold" timing on the originating line.

TECHNOLOGICAL AND FEATURE INTERACTION CONSIDERATIONS:
1. This feature is available in the following central office switches:

   Switch Type			DMS-100
   Earliest Generic Release	BCS24	

   This feature may be available on the 1A ESS switch with custom
   hardware and software.

2. Answer Supervision requires a special line card in the DMS-100.

3. Battery reversal may lag actual answer by upwards of 2 seconds.  This is a
   function of accumulation of network elements processor time (delay) in the
   path of the call connection.

4. Answer Supervision is not provided when calling certain types of non-billing
   lines.

5. Answer Supervision is provided immediately upon connection to an OSPS, 
   TSPS or TOPS system, before actual operator answer.

6. Answer Supervision may be provided before actual answer when calling certain
   types of ACD systems.

7. Battery reversal signals are not passed by the carrier systems that are 
   normally used for pair gain and for foreign exchange service.  Answer
   Supervision is compatible with foreign exchange service provided over 
   physical cable facilities.

8. Many dial long line circuits do not pass battery reversals.

9. The Answer Supervision signal originates at the called end of a built up
   connection and is conveyed back to the originating central office along the
   path of the call.  There are situations where this path is not transparent
   to the Answer Supervision signal.  

10. This service is intended to be used by compatible terminal equipment.  Many
    DTMF telephones are polarity sensitive and do not dial when the line voltage
    is reversed.

11. References:
 o TR-TSY-000506, Section 6.2, Customer Line Signaling for Supervisory States.
 o SR-TSV-002275, BOC Notes on the LEC Networks - 1990.
 o TR-NPL-000334, Voice Grade Switched Access Service.
 o TR-NPL-000335, Voice Grade Special Access Service.
 o Ameritech Answer Supervision With Line Side Interface, AM-TR-MKT-000071,
   Issue 1, August 1990.

This service is associated with the Circuit Switched Line basic serving 
arrangement.
