Bell Communications Research, Inc.

Chi-Leung Lau

Paul E Fleischer

A Residual Time Stamp (RTS) technique provides a method and apparatus for recovering the timing signal of a constant bit rate input service signal at the destination node of a synchronous ATM telecommunication network. At the source node, a free-running P-bit counter counts cycles in a common network clock. At the end of every RTS period formed by N service clock cycles, the current count of the P-bit counter, defined as the RTS, is transmitted in the ATM adaptation layer. Since the absolute number of network clock cycles likely to fall within an RTS period will fall within a range determined by N, the frequencies of the network and service clocks, and the tolerance of the service clock, P is chosen so that the 2.sup.P possible counts, rather than representing the absolute number of network clock cycles an RTS period, provide sufficient information for unambiguously representing the number of network clock cycles within that predetermined range. At the destination node, a pulse signal is derived in which the periods are determined by the number of network clock cycles represented by the received RTSs. This pulse signal is then multiplied in frequency by N to recover the source node service clock.

Synchronous residual time stamp for timing recovery in a broadband

A sychronous frequency encoding technique (SFET) provides method and apparatus for recovering the timing of an isochronous source node input service signal at the destination node of a synchronous ATM telecommunication network despite cell jitter which arises from the broadband multiplexing and switching delays in the network. A source node control clock is employed which is of greater frequency than that of the service signal and as a result a data under-flow condition occurs in the cell assembly process at a rate that is a function of the difference between such clock frequencies. Regular cell transmission is inhibited for a period at each under-flow occurrence and this pseudo-'stuffed cell' gap is signaled by setting a flag bit carried by an ensuing transmitted cell. At the destination node, a timing stream from the control clock, which is synchronous with that of the source node, is regularly gapped by inserting periods of delay according to the ratio of flagged cells in the service transmission, thereby reducing the timing stream by the noted frequency difference and reproducing the original service signal frequency.

Synchronous frequency encoding technique for clock timing recovery in a

A survivable ring network is disclosed that can withstand a cut link or failed node, without the need for a central controller or protection switching among links. The disclosed invention comprises two rings carrying identical multiplexed node-to-node communications in opposite directions. When a system error is detected in a downstream node, error signals are inserted in all subrate channels. Each subrate channel receiver receives identical communications from each ring. If one subrate channel has an error signal, the receiver selects the alternate channel.

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Eatontown, NJ, United States of America

Chi-Leung Lau