Telecom Technical Specifications




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5.4 Transmission characteristics of public automatic switching exchange

5.4.1 General function

5.4.1.1 AC Power Failure


Requirement:

  1. When AC power is failed, PABX should keep at least on line for emergency dialing.

  2. PABX system on restoration of ac power shall keep the services been set up till the time just before the restoration of ac power.

  3. The operation instruction or user manual should have instruction to ac power failed.

Purpose: To assure PBX can provide emergency telephone function when lost or recovery of AC power supplied.

Test method:



    1. Lost of AC power test configuration as Fig. 38.

    2. Test method of AC Power Failure:

  1. Without supplying the AC power to TE.

  2. Set a on line communication to one PSTN line from extension line.Reference the operation manual of vendor.

  3. Plug in the AC power.

  4. Check TE should keep the communication status of being set up.

Test equipment:

  1. Loop Simulator.

Loop Simulator


EUT






AC power source


Figure 38. AC power failure test configuration




5.4.1.2 Release of the PSTN Line


Requirement: The release of PSTN line should be within 3 seconds after the extension line is released or interrupted by console.

Purpose: To prevent call intrusion of PSTN lines.

Test method:


  1. Release the PSTN Line test configuration as Fig. 39.

  2. Test method of Release of the PSTN Line:

  1. Set the extension telephone on line and in communication to PSTN line.

  2. Set the extension telephone off line, the PSTN line will be released.

  3. Record the DC voltage and measure the timing from the extension line released to PSTN line is released.

Storaged Type Oscilloscope

CH1 CH2

Loop


Simulator

EUT


Telephone set




Ext. Port

PSTN Port



Figure 39 Release of the PSTN Line test configuration

Test equipment:



  1. Loop Simulator.

  2. Storaged Type Oscilloscope.

  3. Telephone.



5.4.2 Quiescent state noise


Requirement: The Quiescent state noise of each PSTN port should be less than 1.5mVp ( 36 dBrnc).

Purpose: To assure the quality of communication in PSTN.

Test method:


  1. Quiescent state noise test configuration as Fig. 40.

  2. Quiescent state noise Test method:

  1. Connecting 600Ω load and set a communication to PSTN line.

  2. Bandpass Filter set at frequency of 200 Hz to 4000 Hz.

  3. Measuring the peak noise level at PSTN port.

Note: Bandpass filter and voltameter can be substituded by spectrum analyzer.

Test equipment:



  1. Loop Simulator.

  2. Bandpass Filter.

  3. AC Voltameter.

  4. 600ΩReference Load.


Figure 40 Quiescent state noise test configuration

Loop

Simulator


EUT


600Ω

Reference Load



Bandpass Filter

Ext. Port

PSTN Port

AC Voltmeter

5.4.3 Transmission Loss


Requirement: Transmission loss of extension port to PSTN port should be less than 2 dB.

Purpose: To assure a good quality of through port communication.

Test method:


    1. Transmission loss test configuration as Fig. 41.


AC Voltmeter



C:2uF±10%

Loop Simulator


EUT


600ΩReference

Load

AC Signal Generator

Ext. Port



PSTN Port

sw








Figure 41 Transmission loss test configuration




    1. Transmission loss Test method:

  1. Connecting 600Ω load and set extension port in communication with PSTN port.

  2. Set AC Signal Generator in connection to loop simulator.

  3. Adjust the level of 1000 Hz signal to get 0 dBV output at PSTN port.

  4. Measure the input signal level V1( in dBV) at the extension port.

  5. Caculate the Transmission loss = 0 – V1.

  6. Set AC Signal Generator in connection to 600Ω load.

  7. Adjust the level of 1000 Hz signal to get 0 dBV output at extension port.

  8. Measure the input signal level V2( in dBV) at the PSTN port.

  9. Caculate the Transmission loss = 0 – V2.

  10. Select the higher value from the results of step (5) and (9).

  11. Selecting another port of extensions and PSTN lines, repeat step (1) to (10).

  12. The maximum value get from step (1) to (11) is the Transmission loss.

Test equipment:

  1. AC Signal Generator.

  2. Loop Simulator.

  3. AC Voltmeter.

  4. 600 Reference Load.



5.4.4 Cross talk


Requirement: The crosstalk loss of 1 kHz signal should be more than 65 dB. For any TE with more than two PSTN ports.

Purpose: To assure good quality of communication and not be interfered by another communication lines in another PSTN port.

Test method:


  1. Crosstalk test configuration as Fig. 42.

Spectrum Analyzer



Loop Simulator



600Ω

Reference

Load

C:2uF±10%



Ext.

Port 1

AC Signal Generator




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