Passive test completion
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A passive test termination ( PPA ) is used for measuring purposes in the telephone network . In telecommunications technology, the telephone user is provided with a network operator TAE connection socket (the first installed NFN connection socket or “ 1st TAE ”) as a transfer point ( network termination ) between the network operator and the user. It marks the limit of ownership and responsibility of the network operator.
The PPA consists of a series connection of a diode and a resistor 470 kΩ (± 1%), which are connected between the a-wire and b-wire of the subscriber connection line (see circuit diagram).
The components of the PPA are invisibly integrated in the base of the 1st TAE socket . These sockets can be recognized by the label " 1. " and a typical design and are usually connected using an insulation displacement connector.
In older installations (up to around 1995) the passive test termination can be seen under the TAE cover as a small, black component on the screw terminals (see picture; the third connection of the PPA has no electrical function, it is only used for additional attachment to an in usually unused terminal in the TAE socket).
In normal operation, the diode blocks the direct voltage (around 60 volts) fed into the a / b wire by the local exchange , if the TAE is correctly connected to the a / b twin wire (a-terminal to minus and b-terminal to positive potential ) so practically no current flow can be measured. For testing purposes, the subscriber circuit in the exchange can reverse the polarity of the supply voltage of the connection to be measured. Then the resistance of the PPA (and thus also the resistance of the subscriber line) can be measured. In this way it can be checked remotely with the system-external test technology (SEPT) whether the subscriber connection line up to the 1st TAE of the user corresponds to the requirements with regard to the galvanic measurement values, especially insulation values and external voltage components. In this way, for example, an interruption or a short circuit on the subscriber line can be determined. If there are deviations from the target value, possible errors can be classified more precisely using the measured resistance.
The main purpose of the passive test termination for the network operator is to make a statement as quickly as possible in the event of a malfunction report by the user about whose area of responsibility the error lies, whereby a successful measurement of the SEPT does not allow any statement as to whether the telephone line has been switched to the correct location is. Nor is it possible to detect a frequently encountered defect in the area of the spring contacts of the TAE connection socket, since the components of the PPA are always in the immediate vicinity of the connection terminals.
Until 2002, Deutsche Telekom delivered DSL splitters with an integrated PPA that can be switched off. These could be the “1. Replace TAE “as network termination.
Today's DSL splitters no longer contain a PPA. So if it is occasionally recommended not to connect a DSL splitter to the “1. TAE ", but the" 1. TAE ”and to connect the splitter directly to the subscriber line using the built-in plug-in terminals, then this procedure is undesirable by Deutsche Telekom because a PPA is no longer available. In the area of the Annex-J DSL connection technology, splinterless operation is planned. Basically nothing will be changed on the subscriber line. The PPA in the first junction box is retained. In addition, a connection cable is used in splinterless operation, which contains a few electronic components in the plug that provide a "galvanic signature" for measurement purposes and allow the network provider to determine a plugged modem by measurement, even if it is not synchronous. With a telephone connection using a copper pair, the "1. TAE “with passive test completion continues to be the transfer point.
literature
- Deutsche Telekom AG (Ed.): Technical description of the analogue dial-up connections on the T-Net / ISDN of the T-Com 1 TR 110-1 . Darmstadt August 1, 2007, p. 28, 45, 66 ( telekom.de ( Memento from May 23, 2011 in the Internet Archive ) [PDF; 1000 kB ]).