Introduction To Line Telecommunications

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6. Private Circuit Links
  6.1 - Private Wires And Access Lines
  6.2 - Leased Lines
  6.3 - Digital Leased Lines

6.2.4 - AC15

Also known as Signalling System Alternating Current No. 15 (SSAC15) is a 4-wire connection between PBXs of unlimited distance. It has now replaced AC13 as the long distance inter PBX signalling system.

Signalling is via a signalling frequency of 2280Hz. One pair is used for transmission and the other for reception together with incoming and outgoing speech. Signals are mostly applied (tone on or tone off) continually.

The table below shows the signalling conditions relevant to the call status on the transmit and receive pairs for AC15 A the most common variant of this signalling system.

Link Status Transmission Pair Reception Pair
Idle On On
Seize Off -
Delay Dial - Off
Proceed To Dial - On
Dialling On / Off Pulses -
Answer - Off
Forward Hold Off -
Backward Hold - Off
Clear Forward On >300 ms -
Clear Backward On - >300 ms
Forward Aux On 45 - 135 ms -
Backward Aux On - 45 - 135 ms
Table 4 - AC15 Signals

As with DC10 the Delay Dial, Proceed Dial and Aux signals are optional and are not always used. The meaning of a signal will be determined by the tone state and timing in the call set-up process.





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Introduction To Line Telecommunications
Copyright Panasonic Business Systems UK Ltd 2000