Node Provided With Facility for Checking Establishment of Synchronization

1. A method for checking the establishment of synchronization at a node in a synchronous communication network which performs communication by sending and receiving multiplexed frames, comprising the steps of: forming said frames by successively adding pointers showing header positions to a plurality of data portions; comparing at said node between the value of a pointer included in each data portion received from an opposing node side and the value of a pointer to be added to each data portion, which is the same as the received data portion, and to be sent from a home node; detecting whether the compared values coincide, synchronization being established between the opposing node and the home node when said compared values coincide; demultiplexing each of said frames received at said home node in a received signal from the opposing node into said data portions and said pointers in correspondence with a timing component in the received frames; holding the data in a memory device, successively reading out the held data portions in correspondence with a clock of a clock source in the home node, adding pointers to the read out data portions at the home node showing headers of the data portions to be sent and multiplexing to form frames of a transmission signal from said home node, comparing the pointers demultiplexed from the received frames and the pointers added to the transmission signal, and detecting that a clock of the opposing node that provided the received signal and the clock of the home node are synchronized when the compared pointers are found to coincide, wherein a plurality of clock sources are provided at the home node and a further step of periodically successively selecting and using the plurality of clock sources, one of said plurality of clock sources giving a result with least noncoincidence in the comparison being finally selected and used as a representative clock source for the home node.

2. An apparatus for checking for the establishment of synchronization at a node in a synchronous communication network which performs communication by sending signals and receiving signals of multiplexed frames formed by successively adding pointers showing header positions to a plurality of data portions, comprising: a demultiplexer unit (1) at a home node for demultiplexing a received signal sent from a transmission node into data portions and pointers in correspondence with a timing of the received signal, a memory (2) for holding the demultiplexed data portions, a multiplexer unit (4) for successively reading out the held data from said memory in time with a clock of a clock source (3) of the home node, for adding pointers showing headers of the read out data and for multiplexing said read-out data and added pointers to prepare a transmission signal to be sent from said home node, and a comparing unit (5) for comparing the pointers separated from said received signal by the demultiplexer unit (1) and the pointers added to said transmission signal by the multiplexer unit (4), so as to find whether or not the synchronization between a clock of the transmission node of the received signal and the clock of the home node is established by the resultant comparison and, if it is not established, said clock of said home node is adjusted without adjusting the pointers.

3. An apparatus for checking for the establishment of synchronization at a node in a synchronous communication network which performs communication by sending signals and receiving signals of multiplexed frames formed by successively adding pointers showing header positions to a plurality of data portions, comprising: a demultiplexer unit (1) at a home node for demultiplexing a received signal sent from a transmission node into data portions and pointers in correspondence with a timing component in the received signal, a memory (2) for holding the demultiplexed data portions, a multiplexer unit (4) for successively reading out the held data from said memory in time with a clock of a clock source (3) of the home node, for adding pointers showing headers of the read out data and for multiplexing said read-out data and added pointers to prepare a transmission signal to be sent from said home node, and a comparing unit (5) for comparing the pointers separated from said received signal by the demultiplexer unit (1) and the pointers added to said transmission signal by the multiplexer unit (4), synchronization between a clock of the transmission node of the received signal and the clock of the home node being detected by coincidence in the comparison, wherein said demultiplexer unit (1) includes a demultiplex function unit for said demultiplexing of the received signal into said data portions and pointers, and a first holding unit (63) for holding the demultiplexed pointers, said multiplexer unit (4) includes a multiplex function unit (72) for successively reading out the data portions held in the memory (2), timed by the clock of the home node, and for successively adding said pointers to said read-out data portions indicating the respective headers of the read-out data portions and multiplexing said read-out data portions and pointers to prepare said transmission signal, and includes a second holding unit for holding the added pointers, and said comparing unit (5) detecting the coincidence of the pointers held in the first holding unit (63) and the pointers held in the second holding unit (73) coincidence of said pointers corresponding to synchronization between the clock of the transmission node of the received signal and the clock of the home node.

4. An apparatus for checking for the establishment of synchronization as set forth in claim 3, wherein said multiplexer unit (4) includes a pointer generating unit (71) for adding pointers to said read-out data portions.

5. An apparatus for checking for the establishment of synchronization as set forth in claim 4, further comprising: a pointer detection unit (85) provided in said demultiplexer unit for detecting said received pointers in said received signal, a pointer calculation unit (82) provided in said pointer generating unit (71) for adding said added pointers to said data portions read-out from memory, and a header position memory, connected between said pointer detection unit and said pointer calculation unit for writing detection pulses by a first clock each time the pointer detection unit detects a pointer, reading out detection pulses by a second clock, and causing the calculation of the header position of the received data at the pointer calculation unit.

6. An apparatus for checking for the establishment of synchronization as set forth in claim 3, wherein said demultiplexer unit (1) includes a timing generating unit (61) for extracting the timing component of said received signal.