External testing technology
The system- external test technology ( SEPT ) is a technical facility of communication technology . With the SEPT, the electrical values ( current , voltage , resistance , capacitance ) of a telephone line (subscriber connection line) can be checked in order to make a statement as to where a possible error is to be found when a possible fault is reported.
For this purpose, the SEPT already disconnects the subscriber line in the exchange and then carries out the necessary measurements. During this time, the subscriber cannot use the line. Measurements are made for external voltage , current, line resistance and capacitance. The current measurement can only be successful if the line to the subscriber is not interrupted and if the subscriber has a passive test termination in his junction box . The SEPT changes the direction of tension for the test. The passive test termination, consisting of a series connection of diode and resistor, is switched through and a line measurement can be carried out. A measurement by the SEPT usually takes less than half a minute.
Measurements
Open line
In technical jargon, a line that has been interrupted at any point and does not form a closed circuit (for whatever reason) is referred to as an open line or de-energized . The SEPT is able to measure open lines and still identify the point relatively precisely where the line is interrupted. Since both wires of the subscriber line in a cable as a rule as twisted pair or star quad together twisted , they form the basis of the cable length is of even greater capacity (see: capacitor ), the longer the line is. The incoming wave is reflected at the open cable end (see wave resistance ); this measurement is carried out at a higher frequency. This means that the point of the interruption can be measured to the nearest centimeter, provided that the line parameters are known.
External voltage
The SEPT can measure external electrical energy acting on the telephone line from outside . External voltage usually results from the fact that the line has an unwanted connection with another live electrical cable (for example with another telephone line).
Measurements against earth
It can happen that one of the wires in the telephone line has conductive contact with earth . The wires are measured one after the other. Based on the signal propagation time, it can be determined exactly at what distance the wire has an undesired connection to earth. If the connection is analog , the noises, which do not necessarily have to occur, may be acceptable. Connections with higher requirements, such as ISDN connections, generally no longer work with such a fault.
Messages
loop
With this error message, the SEPT indicates that there is a short circuit between the two wires of the telephone line somewhere along the route of the telephone line. In principle, the value of the measured resistance is also specified. It doesn't necessarily mean that it is really a short circuit. It is possible that a leakage current has formed from A to B through another medium (e.g. water). For example, a 0 ohm loop would be a nearby short at the main distribution board, for example ; in the case of a further short circuit, at least the ohmic resistance of the line is measured up to the point of the short circuit.
Occupied internally
This message is issued when the SEPT determines that the connection is not disturbed. The participant may be on the phone. Internally manned is also reported if there is a fault, which can be inferred from the passively measured electrical values. At this point (this message is issued before the line is disconnected), the user of the SEPT can independently choose whether to disconnect the line for measurement or not to perform a measurement.
use
When reporting a fault in a telephone connection, the person receiving the fault can use the SEPT to check the connection reported as faulty. The test can be carried out from the location at which the fault report was received. As a rule, the SEPT is only possible for authorized employees of the corresponding telecommunications companies. Private individuals do not have access to the SEPT for reasons of data protection .
Extended usage
In various companies it is possible to use the SEPT via any telephone (including a mobile phone ). To do this, a specific service number is dialed, the user authenticates himself with a PIN , selects the desired function from a menu and can thus also check a telephone line from a distance. This is an advantage when a fault on a telephone line has to be eliminated and technical help is required.