34.3.3 Meter pulse detection then the address signalling is regenerated as required towards the public exchange. On any of the 2-wire analogue signalling systems the PABX may A call can be cleared by either the distant end or the PABX also be required to detect meter pulses sent from the exchange. removing the loop from the line giving a disconnect clear. The main These are normally only used on systems where it is necessary to problem for the PABX is knowing when the distant end has cleared provide accurate call accounting within the PABX e.g. in a hotel as the disconnect clear signal is not normally transmitted from one applications or where the PABX is in a multi-tenant environment Address and Earth detect signalling Earth detect detect To control Figure 34.5 Earth calling Private networking 34/7 and the PABX owner charges for the use of the system on a timed number can be used as an additional check when accessing a basis related to the meter pulses received from the public exchange. data base via a CSTA link. Two signalling systems are in use for meter pulse detection and 4. Call charge indication is an attractive feature for PABX appli- both use out of band signalling as it is necessary to send the meter cations in hotels. It provides information on customer origin- pulses to the PABX during the conversation phase of the call and the ated calls and, in the basic PABX, an input to the call talkers should not be able to detect the pulses. 50Hz longitudinal management packages. At the end of each call the network pulses are applied to the speech pair and the trunk circuit of the reports the number of units used and the cost of the call. PABX must therefore be equipped with a detector which senses the 5. Network address extension is only available on category 1 calls meter pulses and then passes them onto the system controller for and enables a destination code to be appended to the PSTN assimilation with the call record. The other method uses 12kHz or number. The feature can be used to access a specific device