| 摘要 |
On a concentrator-internal PCM line between the connection units, e.g. collective subscriber connection circuits or connection line collective termination circuits, of a concentrator and the PCM device (digital line unit) common to them, which PCM line is connected in the concentrator to a PCM transmission system (time division multiplex line) leading to the higher-level exchange and which can also perform switching operations in emergency mode to set up internal connections (island exchange mode) if the higher-level exchange or PCM transmission system fails, the channels, which, on the one hand, serve to transmit the frame alignment word in the PCM transmission system and which, on the other hand, are used as a signalling channel, are used to transmit audible tone signals from an audible tone generator provided in the PCM device to the connection units where the injection of audible tone signals into subscriber connection lines or connection lines or corresponding channels is controlled on a connection-specific basis. <IMAGE>
|
