External/internal clock synchronization in ATM-based distributed systems

We present a clock synchronization algorithm, based on recent results on convergence functions, designed to achieve external and internal synchronization over ATM. We take advantage of transmission delay and delay variation control granted by ATM networks to achieve high precision required to ensure real-time capabilities or distributed data coherence. Precision of the algorithm mainly depends on cell transmission jitter that introduces uncertainty in time determination. Cell delay variation is heavily reduced by the use of ATM Continuous Bit Rate (CBR) point-to-multipoint connections to exchange timestamps. The use of the ATM multicast capability allows one to reduce the required CBR bandwidth. The algorithm achieves a synchronization closer than 100 /spl mu/s, despite F/sub clock/ arbitrary clock failures and F/sub crash/ node crashes on at least 3F/sub clock/+1+F/sub crash/ nodes. An implementation model for high-precision, combining ATM Operation And Maintenance (OAM) cells and network adapter firmware is described, and is currently implemented in the ANTARA technology.

[1]  Flaviu Cristian,et al.  Continuous clock amortization need not affect the precision of a clock synchronization algorithm , 1990, PODC '90.

[2]  Flaviu Cristian,et al.  An optimal internal clock synchronization algorithm , 1995, COMPASS '95 Proceedings of the Tenth Annual Conference on Computer Assurance Systems Integrity, Software Safety and Process Security'.

[3]  Sam Toueg,et al.  Optimal clock synchronization , 1985, PODC '85.

[4]  Paulo Veríssimo,et al.  A posteriori agreement for fault-tolerant clock synchronization on broadcast networks , 1992, [1992] Digest of Papers. FTCS-22: The Twenty-Second International Symposium on Fault-Tolerant Computing.

[5]  Sam Toueg,et al.  A Modular Approach to Fault-Tolerant Broadcasts and Related Problems , 1994 .

[6]  Hermann Kopetz,et al.  A synchronization strategy for a time-triggered multicluster real-time system , 1995, Proceedings. 14th Symposium on Reliable Distributed Systems.

[7]  Ulrich Schmid.  Synchronized UTC for Distributed Real-Time Systems , 1994 .

[8]  Nancy A. Lynch,et al.  A new fault-tolerant algorithm for clock synchronization , 1984, PODC '84.

[9]  Nancy A. Lynch,et al.  A New Fault-Tolerance Algorithm for Clock Synchronization , 1988, Inf. Comput..

[10]  Peter Key,et al.  CDV in ATM Networks — Performance Results from the Fairisle ATM Testbed , 1994 .

[11]  Danny Dolev,et al.  On the possibility and impossibility of achieving clock synchronization , 1984, STOC '84.

[12]  Hermann Kopetz,et al.  Clock Synchronization in Distributed Real-Time Systems , 1987, IEEE Transactions on Computers.

[13]  Fred B. Schneider,et al.  Understanding Protocols for Byzantine Clock Synchronization , 1987 .