| 摘要 |
The invention relates to a circuit and a method, characterized in that an independent, local control unit (7) which monitors a back-up terminal cooperates to a limited extent with the data transmission apparatus of the user and from the analysis of a data control signal recognizes the presence of a case of substitution switching. Via lines (10 to 14) and modems (15) said control unit (7) switches on the transmission carrier (19) of the satellite modem (15) affected, which is connected to a satellite antenna (18). The satellite antennae (18) are connected to the satellite (20) via the transmission carrier (19). All other terminals in the network which are not affected also receive the transmission carrier (19) of the satellite modem (15) concerned. In this way the transmission capacity of the asynchronous overhead of the satellite modem (15) is used for the transmission of target addresses. A hub (4) is connected to the terrestrial network (1) via an interface card or a modem (5), which network in turn is connected to routers (6) by means of lines (2 or 3). Customer installations (8) or terminals (9) are connected to the routers (6) by means of lines (10).
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