SSAC15A is an in-band continuous tone line signalling system used for the transmission of
digit pulses and supervisory signals on both way inter-PBX circuits where a suitable DC
path is not available. i.e. Over long distances. In nearly all occurrences
the circuit will have to amplified.
BASIC SSAC15A CIRCUIT
The system requires a 4-wire presented circuit between the two PBXs and employs a single
tone frequency of 2280 Hz for signalling in each direction of transmission. When the
circuit is in an idle state the 2280 Hz signalling tone is continuously present in both
directions of transmission and therefore the SSAC15A is described as a Tone-on-Idle
Low Level Tone is a tone sent at -20 dBm0
High Level Tone is a tone sent at -10 dBm0
On modern electronic PBX's that support AC15A it is normal to simply terminate the 4 wire
circuit onto an AC15A interface card which slots directly into the appropriate position in
the PBX. On older PABX's or electronic PABX's/CCS's that do not support AC15A it is normal
to terminate the 4 wire circuit onto a signalling unit which provides an AC15A to DC5
The signal frequency is transmitted to line at two standard levels: -10 dBm0 (High Level)
and -20 dBm0 (Low Level). The signal receiver has the same sensitivity in each case. It
will accept signal levels in the range: -3 dBm to -29 dBm.
Note:- Level measurements should be made on Transmit and Receive of the 4 wire.
If the 'transmit' pair is disconnected, the trunk at the distant PBX will be PG
(Permanent Glow - i.e. locked out). PBX calls
at the local end will fail.
Monitoring of Circuit
Listen on transmit and receive pairs for 'Tone on Idle' signal. You will need a high
impedance telephone or other suitable listening device. This is a quick check to see
whether a tone is being sent from the local end on the transmit pair and being received
from the distant end on the receive pair.
Using this method you may also monitor signalling tones being sent when circuit is in use.
To prove the level of these tones you will need a Line Measuring Set.
Loop back test
Using a suitable Patching cord connect the transmit and receive at the local end together.
Ensure that the line is totally disconnected from the distant end. If the circuit goes
normal then the local end is ok.
If two circuits are available then these can be connected together (ensuring all distant
ends are disconnected). The two circuits should go idle and calls should be able to be
made in and out of the local end.
SSAC15B is the preferred method of inter-PBX signalling on circuits over any 4 wire
presented transmission path where SSMF5 inter-register signalling is employed.
Transmission requirements are as described in SSAC15A section.
Methods of Testing The methods of testing are the same as those described
in the AC15A section.
SSAC15C is used to provide external extension and out of area exchange line signalling
with recall facilities. Signalling Units 53A and 54A are used. For description of circuits
refer to Signalling Units 53A and 54A.
SSAC15D is an in-band signalling system used on International inter-PBX circuits or
appropriate inland inter- PBX circuits. It uses a single frequency of 2280 Hz in each
direction of a 4 wire transmission path.
SSAC15A but sending MF tones instead of Loop Disconnect dial pulses.
Transmission Requirements are as described in SSAC15A section.
Methods of Testing Circuits
The methods used for testing a SSAC15D circuit are the same as those described in the