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 Method of synchronization status message processing in transmission apparatus

Details
Inventors: Meki, Seiji; Yamada, Shunji; Moriyama, Junichi;
Assignee: Fujitsu Limited (Kanagawa, JP)
Primary Examiner: Ngo; Ricky
Assistant Examiner:
Attorney, Agent or Firm: Helfgott & Karas, P.C.

A transmission apparatus has units to which main signals are input for subjecting these main signals to predetermined processing and then transmitting them. One of these units is a master unit and the others are slave units and they are interconnected by a clock cable and processor-to-processor cable. Each slave unit detects a synchronization status message that has been inserted into a main signal input from a line and notifies the main unit of this synchronization status message via the processor-to-processor cable. Using synchronization status messages acquired from the slave units and a synchronization status message that has been inserted into a main signal input thereto, the main unit obtains the synchronization status message indicative of the best quality level and adopts, as a master clock, a clock extracted from the main signal into which this synchronization status message has been inserted.

DETAILED DESCRIPTION Accordingly, an object of the present invention is to lighten the load on the master shelf by dispersing the synchronization status message detection processing among the shelves (the master shelf and slave shelves).
Another object of the present invention is to lighten the load on the shelves, especially the master shelf, by sending and receiving synchronization status messages indicating quality via a processor interconnecting cable between the master shelf and slave shelves only when the quality of a clock changes or only when the quality of the master clock changes, and refraining from sending and receiving synchronization status messages if there is no change in quality.
Another object of the present invention is to prevent loss of synchronization in a network by so arranging it that another transmission apparatus will not use a master clock even if the unit of the master that decides the master clock malfunctions.
A further object of the present invention is to prevent loss of synchronization in a network by so arranging it that another transmission apparatus will not use a clock, which is contained in a main signal sent from a slave shelf, even if the unit of the master shelf that selects and processes the master clock sent from the master shelf malfunctions.
Still another object of the present invention is to set synchronization status messages, which indicate the qualities of the clocks, in the overhead S1 bytes of main signals sent from slave shelves even in a case where the cable for sending the master clock is severed and slave shelves use the HO clock or INT clock as the reference clock.
Yet another object of the present invention is to prevent unnecessary changeover of clocks within a network, as well as loss of synchronization in the network, by so arranging it that even when a self-timing clock such as the HO clock or INT clock is being used as a reference clock during the execution of processing to decide the master clock, a synchronization status message indicating the quality of this clock is not transmitted


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