Common control framing detector

摘要

The PCM encoded digital data groups transmitted to a switching office are respectively stored a frame at a time and then read out from store in a sequence such that a plurality of digital groups are multiplexed on to a common bus. A common control framing detector continually monitors, at the multiplex point, all of the digital groups on a time multiplexed basis. The framing pattern status of each group is stored in a shared recirculating memory, which is continually updated in accordance with changes introduced into each group signal by the switching office for synchronization and reframing purposes. The stored framing pattern status of each digital group is compared with the group framing bits as each group appears on the multiplexed bus. If the comparison fails, an error signal is generated. An error timing store counts the error signal for each group and when the error count of a given group reaches a predetermined threshold an out-of-frame signal is generated which initiates a reframe operation for the out-of-frame group.