Sync messaging examples

Overview

In this section, some detailed examples are given to show specifically how the sync messages propagate through network and assist in the recovery from a fiber failure. Through these examples, one can extend the same concept to any other network that may include different topologies, number of sites, failure locations, and number of BITS clocks.

Synchronization reconfiguration in an access ring

The following figure, Part A, illustrates an access ring operating in its normal configuration. The Alcatel-Lucent 1665 DMXtend shelf at the CO is externally timed, and each of the other Alcatel-Lucent 1850 TSS-5 shelves are line timed in a counterclockwise direction. The STU message is sent to indicate where timing is traceable to an external BITS and where it is valid to be used. The DON'T USE message is sent on the interface that is being used as the line timing reference and, thus, where using that timing would create a timing loop. Sync messaging and automatic synchronization have both been enabled for this network.

In the following figure, Part B, a fiber has been cut between sites A and B. Immediately, the Alcatel-Lucent 1850 TSS-5 shelf at site B enters holdover and sends out the STU message to site C. The Alcatel-Lucent 1850 TSS-5 shelf at site B cannot switch to line time from site C because it is receiving the DON'T USE message on that interface.

Figure 6-5: Automatic synchronization reconfiguration, part A and B

In the following figure, Part C, the Alcatel-Lucent 1850 TSS-5 shelf at site C detects the incoming Traceable Stratum 3 message and sends the message to site D. The Alcatel-Lucent 1850 TSS-5 shelf at site C cannot switch to line timing from the other rotation because it is receiving the DON'T USE message on that interface.

In the following figure, Part D, the Alcatel-Lucent 1850 TSS-5 at site D detects the incoming Traceable Stratum 3 message. The STU message is a better quality message than the SONET Minimum Clock message, so the Alcatel-Lucent 1850 TSS-5 shelf at site D switches to line timing from site A. After the switch occurs, the DON'T USE message is sent back to site A, and the STU message is retransmitted to site C.

Figure 6-6: Automatic synchronization reconfiguration, part C and D

In the following figure, Part E, the Alcatel-Lucent 1850 TSS-5 shelf at site C detects the incoming STU message from site D. The STU message is a better quality message than the SONET Minimum Clock message being received from site B, so the Alcatel-Lucent 1850 TSS-5 shelf at site C switches to line time from site D. After the switch occurs, the DON'T USE message is sent back to site D, and the STU message is retransmitted to site B.

In the following figure, Part F, the Alcatel-Lucent 1850 TSS-5 shelf at site B detects the incoming STU message from site C. The STU message is a better quality message than the internal holdover capability, so the Alcatel-Lucent 1850 TSS-5 shelf at site B switches to line time from site C. After the switch occurs, the DON'T USE message is sent back to site C, and the STU message is forwarded to site A. When the failure clears, the synchronization remains in the new configuration unless it is manually switched back.

Figure 6-7: Automatic synchronization reconfiguration part E and F