This page gives technical information on the PSTN interface presented by Telecom Eireann to its customers . It covers exchange types in use, line voltage and feed conditions and tones and signals generated by the telephone network . While every effort has been made to ensure that the contents are accurate , there may be situations which are not covered.
Presently there are three exchange types in use, Ericsson AXE, Alcatel E10 and Ericsson Crossbar. The Ericsson AXE and Alcatel are both digital switches, the Ericsson Crossbar is an analogue (electro mechanical) switch.
At present DTMF dialling can be used on approximately 97% of lines.
| Exchange Voltage | 44-56 V DC |
| Feed Bridges | 2 X 400 ohm for AXE and some E10B exchanges. |
| 2 X 200 ohm for electro-mechanical exchanges and the remainder of the E10 lines. | |
| Line Current | 19 - 60 mA for AXE and E10B exchanges. |
| 19 - 100 mA for electro-mechanical exchanges. | |
| In some areas local loop carrier systems are in use. The line voltage on these varies between 6 V - 48 V depending on type. | |
| Some E10 lines are fed using 40 mA constant current feed. | |
The maximum allowable line resistance is 1800 ohms, which is approximately 10 Km of 0.5mm conductor.
| Frequency | 25 Hz |
| Voltage | 75 V rms on AXE and crossbar exchanges. |
| 40 V rms on each leg, out of phase on E10B exchanges. | |
| Cadence | 0.4 s ON, 0.2 s OFF, 0.4 s ON, 2.0 s OFF repeated. |
| In some areas local loop carrier systems are in use which have ringing voltages as low as 45 volts. The voltage presented to the terminal equipment may be as low as 30 volts depending on line length and ringing impedance of the equipment. | |
Register recall is achieved by the terminal breaking the loop condition for a period of between 80 and 300 ms
The network generates tones and signals to give an indication of the call progress to the user or automatic terminal. Click on the highlighted text to download a .wav sample of the tone.
There are a number of dial tones in use, different tones are used to remind the user that call diversion has been invoked or there may be a public voice mail message waiting.
| Frequency | 400 - 450 Hz [Nominally 425 Hz] |
| Cadence | Continuous for normal dial tone. |
| Level | -12 to - 28 dBm depending on exchange type and line length. |
| 410 ms ON 50 ms OFF [Call diversion on AXE exchanges] | |
| 200 ms ON 200 ms OFF [Call diversion on E10 Exchanges] | |
| New Dial Tones. | 400 Hz for 400 ms followed by 440 Hz for 400 ms repeated. [call diversion] |
| 400 Hz for 320 ms followed by 440 Hz for 40 Hz repeated. [message waiting] | |
| The new call diversion tone will replace the existing call diversion tone on both AXE and E10 exchange types. | |
Progress tone is sent by some exchanges to give the caller an indication that the call is being switched.
| Alcatel E10 | Fequency | 425 +/- 5 Hz |
| Level | -12 to -26 dBm | |
| Cadence | 60 ms ON / 60 ms OFF repeated. | |
| Ericsson Crossbar | Ticking tone | Spike type pulses |
| Amplitude | 5 V pk | |
| Cadence | 0.5s repeated. |
This tone is used to indicate to the user that the number dialled is not a valid number.
| Frequency | 950 +/- 5 Hz, 1400 +/- 5 Hz, 1800 +/- 5 Hz. |
| Level | -12 to - 28 dBm |
| Cadence | Silent period of 1000 +/- 250 ms followed by 3 tones of increasing frequency, each of 330 +/- 70 ms duration repeated. |
| Frequency | 400 + 450 Hz for AXE and E 10B. |
| 425 Hz +/- 5 Hz modulated with 50 Hz for Ericsson Crossbar. | |
| Level | -12 to -28 dBm. |
| Cadence | 0.4 s ON, 0.2 s OFF, 0.4 s ON, 2.0 s OFF repeated. |
| 0.4 s ON, 0.2 s OFF, 0.4 s ON, 2.4 +/- 0.2 s OFF in some crossbar exchanges. |
| Frequency | 400 - 450 Hz |
| Level | -12 to -28 dBm. |
| Cadence | Cadence varies with exchange type and call routing, it will be between 0.375s ON / 0.375s OFF and 0.75s ON / 0.75s OFF |
| Frequency | 12 KHz +/- 1% |
| Maximum level | 2.6 V rms |
| Minimum level | 45 mV rms |
| Pulse length | 120 +/-20 ms |
| Due to the ongoing reduction in Telecom Eireann's charges meter pulses are no longer updated and will therefore not be accurate. They are still valid as answer signal detection. | |