Synchronism establishing method and apparatus

A synchronism establishing apparatus for a system which includes a combination of two or more modules of different types having independent synchronism establishing means, the modules including at least one master side module and at least one slave side module, the synchronism establishing method selectively switching an operating one of said modules to effect transmission of a signal through a selected module, the signal having a succession of information frames, and the modules responding to different frame patterns, with synchronism being established by a predetermined number of protection stages, each protection stage including at least one of said information frames, comprising:

• frame pull in processing means provided in each of said modules and serving as said synchronism establishing means when a signal is to be decoded;
• synchronism establishment notifying means for delivering, when establishment of synchronism is detected by said frame pull in processing means the master side module, a notification of the establishment of synchronism of the master side module from said frame pull in processing means of said master side module to said frame pull in processing means of the slave side module;
• mode changing means provided for each of the slave side module or modules for changing, when the slave side module is in a condition wherein synchronism is established when the notification of establishment of synchronism is received from said master side module, the synchronizing operation of said frame pull in processing means of the slave side module into a waiting mode;
• phase maintaining means provided for each of the slave side module or modules for determining, even when a number of abnormal synchronization patterns greater than the number of protection stages are detected after the transition to the waiting mode by said mode changing means, no pull out condition and maintaining a pulled in phase;
• and
• processing operation resuming means provided for each of the slave side module or modules for determining, when said frame pull in processing means of the slave side module detects a notification from the master side module that a pull out condition has occurred, the slave side module determines a normal synchronization pattern at several stages just prior to the reception of the notification, in which the number of the stages is smaller than the number of protection stages for pull in from any condition wherein synchronism is not entered other than during the waiting mode, then the slave side module resumes its processing operation.

A synchronism establishing method for a system which includes a combination of two or more modules of different types having independent synchronism establishing means, the synchronism establishing method selectively switching an operating one of said modules to effect transmission of a signal to a second combination of two or more modules on a receiving side, wherein

• said modules have frame periods set so as to present a ratio in integral number between them, and the frame periods are synchronized on the transmission side, and
• on the receiving side,
• when synchronism is entered with any of said modules, a notification of a timing based on the synchronism is delivered to each of the other module or modules on the receiving side,
• and in each receiving side module, hunting of a synchronization pattern is performed based on the timing and then, when a pull out condition of an operative one of the receiving side modules is detected, the receiving side module is switched immediately if synchronism is established with a waiting receiving side module with a number of pull in frame periods which is set smaller than the number of frame periods for pull in from a condition wherein synchronism is not entered.

A synchronism establishing apparatus for a system which includes a combination of two or more modules of different types having independent synchronism establishing means, the modules including at least one master side module and at least one slave side module, the synchronism establishing apparatus selectively switching an operating one of said modules to effect transmission of a signal to a selected one of a second combination of two or more modules on a receiving side, the signal having a succession of information frames of a predetermined period, comprising:

• frame synchronizing signal generating means provided for each of said modules on the transmitting side and used upon coding of a signal;
• synchronizing means provided for each of said modules on the transmitting side for causing a timing signal to be communicated between said frame synchronizing signal generating means of said modules on the transmitting side to synchronize the frame periods on the transmitting side;
• frame pull in processing means provided for each of said modules on the receiving side and used as said synchronism establishing means upon decoding of a pull in signal, the pull in signal including a predetermined number of information frames;
• and
• notifying means provided for each of said modules on the receiving side for delivering, when synchronism is entered with said frame pull in processing means of a first receiving side module, a synchronizing timing signal based on the synchronism to said frame pull in processing means of a second receiving side module or modules;
• wherein said frame pull in processing means of each of said second receiving side module or modules effects hunting of a synchronization pattern based on the synchronizing timing signal and effects, when a pull out condition of the first receiving side module which has delivered the synchronizing timing signal is detected, switching of the first receiving side module immediately if synchronism is established with a number of pull in frames set smaller than a number of protection frames for pull in from a condition wherein synchronization is not entered.