No relevant resource is found in the selected language.

This site uses cookies. By continuing to browse the site you are agreeing to our use of cookies. Read our privacy policy>Search


To have a better experience, please upgrade your IE browser.


Voice Feature Guide 01

Rate and give feedback:
Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
Features of the POTS Line Interface

Features of the POTS Line Interface

Standards of the POTS Line Interface

Major standards of the voice line interface are as follows:
  • ITU-Q552: It defines transmission specifications of the Z interface.
  • ES 201970: It defines basic hardware features of the voice interface.
  • YD751 - Network Entry Checking Methods for Telephone Exchange Equipment: It describes the voice interface standards defined by China.

The voice technologies have gone through a long period of development. Almost every country has its own standards. The preceding standards are related to the basic features of service boards. Special features must be tailored to meet requirements of different countries.

Basic Features of the Interface

Basic features of the Z interface supported by the voice interface board of the access device are summarized as follows:

  • Battery feeding (B)
    • Batter feeding refers to the supply of the voltage and the current to terminals (such as telephones) to ensure the normal operation of terminals.
    • When the telephone is in the on-hook state, the voltage of the board of the access device is generally 48 V. When the telephone is in the off-hook state, the board of the access device supports the constant-current feeding at 20 mA, 25 mA, or 30 mA. The feeding current can be configured according to the actual requirement.
    • The off-hook feeding of the port can be automatically adjusted. If the length of the loop is short, the port is fed with the constant current. If the length of the loop is long, the port automatically adjusts the loop current based on the preset threshold. This design ensures the compliance with the related standards and optimizes the power consumption of the port.
    • If the feeding current is 25 mA and the voltage is -48 V, the feeding current is equal to or larger than 25 mA when the loop resistance is less than 1200 ohm, and the feeding current is larger than 18 mA when the loop resistance is 1800 ohm.
    • The boards of the access device also support the 40-mA feeding current. The 40-mA feeding current increases the power consumption of ports and thus is not recommended. If the 40-mA feeding current is configured, the number of ports configured with the 40-mA feeding current cannot exceed five on each board.
  • Ringing (R)
    • Ringing refers to the supply of the ring current to telephones so that telephones can ring to inform subscribers of incoming calls. The service boards of the device are designed with the balanced ringing feature.
    • The concept of the balanced ringing is put forward based on the concept of the traditional imbalanced ringing. The traditional imbalanced ringing is classified into two types: (1) In a subscriber line, A line is 0 V and B line is -48 V DC overlaid with the 75 Vrms AC signals. (2) In the subscriber line, A line is -48 V and B line carries the 75 Vrms AC signals. In the case of the balanced ringing, both A and B lines of the subscriber line have the AC signals. The AC signals of the A and B lines are of the same frequency and opposite phases, that is, differential signals. The frequency of signals in the case of the balanced ringing can be set to 16 Hz, 25 Hz, or 50 Hz.
    • The amplitude of the ringing current can reach up to 70 Vrms. The amplitude of the ringing current on a terminal can exceed 35 Vrms if the line impedance is 1400 ohm (5-km lines with the core diameter of 0.4 mm) and the terminal impedance is 4000 ohm. The amplitude of the 50-Vrms ringing current is configurable. This configuration is mainly applicable to the short loop with a length less than one kilometer, aiming to substantially reduce the power consumption of ringing on the ports.
    • The DC offset provided by service boards can reach 20 V, which ensures reliable ringing when the distance is long.
    • The break-make ratio of the ringing current can be configured to meet requirements of different carriers in the world.
  • Over-voltage protection (O)

    Over-voltage protection is one of the interface protection measures.

  • Supervision (S)

    Supervision refers to the detection of telephone state, such as on-hook, off-hook, and off-hook in the ringing state. The terminal state can be learned through detection. The terminal state detection is the basis of some calls.

  • Code/Decode (C)

    Coding/Decoding refers to the process that analog signals of the subscriber line are converted into digital signals and compressed according to the A/U law.

  • H - Hybrid circuit

    Hybrid circuit refers to the conversion from the 2-wire analog interface to the 4-wire digital interface on the board and implementation of the balanced matching with the impedance of the subscriber line.

  • Test (T)

    For details about the test function, see Voice Test and Maintenance.

Interface Impedance, Transmission Specifications, and Gain

The voice interface board of the access device supports the configuration of the interface impedance and gain.

At present, sixteen common interface impedances can be configured, see as the Table 1-14:
Table 1-14 Lists of common interface impedances


Impedance of port and usage description


(200+680|| 100nf): bureau machine in China


(200+560|| 100nf): user machine in China


600ohm: a common interface


(150+510|| 47nf): interface of Russian


(220+820|| 115nf ): widely used in countries like Germany


(220+820|| 120nf ): widely used in Germany


900ohm: seldom used


(800|| 50nf): interface of Brazil


(Zin=87+1052||228nF+229||28.4nF, Zload=93+615|| 471nF+179||495nF+244||32nF): interface of BT0


(Zin=370+620|| 310nf,Zload=600): interface of HK_BT3


(Zin=270+264|| 357nf+1434|| 265nf,Zload=600): interface of HK_BT5


(BT0 without AGC): interface of BT1


(Zin=87+1052||228nF+229||28.4nF, Zload=270+264|| 357nF+1434||265nF): Interface of BT2


(Zin=87+1052||228nF+229||28.4nF, Zload=164+162|| 363nF+1227||350nF): interface of BT3


(Zin= 270+750|| 150nf): a common interface widely used in Europe


(Zin= 370+620|| 310nf ): interface of New Zealand

The interface transmission gain is also configurable. The send gain is generally in the range of +4 dB and -6 dB and the receive gain is in the range of 0 dB to -12 dB. The gain can be configured at the step of 0.5 dB.

The transmission specifications of the service boards are fully compliant with the ITU-Q522 test requirements. If the interface impedance is not one of the preceding eight types, independent software can be developed to support the interface impedance.

Digit Collection

The voice interface board of the access device supports the pulse-based digit collection.

Old-fashioned telephones generally adopt the pulse dialing mode, while new telephones adopt the DTMF dialing mode. Most telephones support the pulse dialing mode.

The service boards support the pulse-based digit collection at the speed of 8 pps to 12 pps. The break-make ratio is in the range of 50% and 80%. The interval of pulses is configurable and is in the range of 100 ms and 2 s. The default interval of pulses is 300 ms.

The DTMF digit collection is completed by the DSP instead of the service boards.

Charging Signals

Service service boards support three charging modes, namely polarity reverse, 12/16KC, and counter impulse delivery.

  • Polarity reverse: The voltage polarity between A and B lines of the subscriber line is reversed. Some terminals detect this type of reverse for charging purpose.
  • 12/16KC: The service board sends the 12000 Hz/16000 Hz sine AC signals at a specific interval to the terminals.
  • Counter impulse delivery: The service board sends pulse signals to the terminals. Charging is implemented based on the pulse signals.

All ports of the service board support both the fast and slow polarity reverse features. Fast polarity reverse is generally completed within 3 ms, which meets the time requirements of polarity reverse of some telephones. Slow polarity reverse is generally completed within 80 ms. It can substantially reduce the interference to the line during the polarity reverse and is compatible with the DSL transmission on the same line.

The service board supports the 12/16KC charging. In the 12/16KC charging mode, the amplitude of the 12/16KC signals is configurable. The amplitude can be set to 0.45 Vrms, 0.775 Vrms, 1 Vrms, 1.5 Vrms, 2 Vrms, or 2.5 Vrms. The maximum value is 2.5 Vrms (200 ohm). In addition, the break-make ratio of KC signals is also configurable. By default, the Make duration is 100 ms and the Break duration is 300 ms. Both the Make duration and the Break duration range from 10 ms to 500 ms.

The service board also supports the counter impulse delivery charging. Some attributes of this charging mode, such as the pulse width and number of pulses sent per minute, are configurable.

Current Reduction of Locked Ports

When a phone connected to a port is in off-hook state for a long time but the conversation is not going on, the service board can lower the current of the port to less than 12 mA to reduce the power consumption of the port.

Short Loop Feeding

When the length of the line is short, the service board uses the low voltage for feeding to reduce the power of the port. When the length of the line becomes long, the service board automatically uses the voltage higher than the previous low voltage to meet the application requirement.

Power Cut-off

Feeding of ports that are not allocated with numbers can be cut off to reduce the power consumption of the ports.

On-Hook Transmission

Service boards support the on-hook and off-hook transmission functions, such as the caller identification display service and the fixed network short message service.

Ringer Equivalence Number

Ringer equivalence number (REN) refers to the number of telephones that can be connected to the same port.

Updated: 2019-02-22

Document ID: EDOC1100067358

Views: 16390

Downloads: 170

Average rating:
This Document Applies to these Products
Related Documents
Related Version
Previous Next