APPARATUS FOR RETIMING AND REALIGNMENT OF STS-1 SIGNALS INTO STS-3 TYPE SIGNAL

摘要

Apparatus and methods for retiming an STS-3 type signal are provided. The SPE of an incoming STS-3 type signal is demultiplexed into three STS- 1 payloads and fed to three FIFOs, and a byte which is synchronous with the TOH is tracked through the three FIFOs to provide an indication of the FIFO depth. A frame count is also kept to track the number of frames since a last pointer movement. Stuffs or destuffs are generated based on the FIFO depth as well as based on the frame count, with a stuff or destuff generated as quickly as four frames from a previous pointer movement if the FIFO is close to full or close to empty, and less quickly (e.g., at thirty-two frames from a previous pointer movement) if the FIFO is only starting to empty or to fill. Where the STS- 3 type signal is a STS-3C signal, the decision on whether to stuff or destuff is made with reference to all three depth measurement circuits as all the STS-1 payloads must be stuffed or destuffed together. Also, to realign the STS- 1 components of the STS-3C signal, the J1 bytes of the signal are tracked through the FIFOs, and a logic circuit is provided having phase 3 of the outgoing STS-3 clock, and the three J1 byte control signals as inputs. The logic circuit inhibits a read of a J1 byte from any particular FIFO unless all FIFO's have a high J1 signal at phase 3 of the clock.