| 摘要 |
In a network of the synchronous-digital hierarchy (SDH), synchronisation signals at standard frequency must be transmitted from one network node (NK1) with a frequency standard (FN) to all the other network nodes (NK2-NK8) in STM-N signals. They are to be the beat of the STM-N signals. If all beats are lost in a network node (N1-N8) along the transmission path of the synchronous beat this node, in holdover mode, generates its own beat at a frequency which no longer corresponds to that of the synchronous beat and is less stable. The next node does not recognise this fault. If it contains a cross-connect device not even a message is any use because it has devices for deriving the synchronous beat only at fixed inputs and what is received at another input is no use to it. If, instead, according to the invention, the beat of a virtual container is used as the synchronous beat, it can be received at any input since the assessment of the virtual container takes place with the cross-connect device only on the output side and there the virtual container is taken parallel to a synchronisation signal recovery arrangement. |
