Patent ID: 8379669

Claim:
A conversion apparatus comprising: a first interface unit connected to an asynchronous communication network to receive a packet signal transmitted from the asynchronous communication network, the packet signal including a special packet into which a first clock signal is converted; a signal conversion unit configured to convert the packet signal into an intra-apparatus signal; a packet-discard determination unit configured to determine the packet signal is discard if no packet signal is received during a predetermined period and to generate a packet discard signal in response to the determination, a clock reproduction unit configured to reproduce the first clock signal based on the special packet included in the intra-apparatus signal; a clock selection unit configured to receive an external clock signal and the first clock signal and to select the external clock signal or the first clock signal as a reference clock signal, the external clock signal being generated at an external device, a loss-of-synchronization determination unit configured to determine whether or not a loss-of-synchronization error occurs in the reference clock signal and to generate a loss-of-synchronization signal the loss-of-synchronization error occurs in the reference clock signal; an alarm control unit configured to generate a first control signal if the packet discard signal or the loss-of-synchronization signal is not generated, to generate a second control signal if the external clock signal is selected as the reference clock signal and the loss-of-synchronization signal is generated, or if the first clock signal is selected as the reference clock signal and at least one of the packet discard signal and the loss-of-synchronization signal is generated, and to generate a third control signal if the external clock signal is selected as the reference clock signal and the packet discard signal is generated; a framer configured to convert the intra-apparatus signal into a data stream in accordance with the reference clock signal in response to the first control signal, to generate an alarm signal for cutting off communication in response to the second control signal, and to generate a synchronous signal in response to the third control signal; and a second interface unit connected to a synchronous communication network to transmit one of the data stream, the alarm signal, and the synchronous signal to the synchronous communication network.