Central synchronization subsystem

The timing subsystem has a central clock located on the CPM. The timing subsystem performs several functions of the network element clock as defined by Telcordia (GR-1244-CORE) and ITU-T G.781 standards.

The central clock uses the available timing inputs to train its local oscillator. The number of timing inputs available to train the local oscillator varies per platform. The priority order of these references must be specified. This is a simple ordered list of inputs: (ref1, ref2, BITS (if available)).

The CPM clock output can drive the clocking for all line cards in the system. The routers support selection of the node reference using Quality Level (QL) indications. The recovered clock can derive its timing from one of the references available on that platform.

The recovered clock can derive the timing from any of the following references (also shown in Figure: Logical model of synchronization reference selection on 7210 SAS):

• synchronous Ethernet ports

  On the 7210 SAS-T (includes all variants), 7210 SAS-R6, 7210 SAS-R12, 7210 SAS-Sx 1/10GE (all variants), 7210 SAS-S 1/10GE (all variants), and 7210 SAS-Sx 10/100GE

• 1588v2/PTP timeReceiver port

  On the 7210 SAS-T (includes all variants), 7210 SAS-R6, 7210 SAS-R12, 7210 SAS-Sx 1/10GE (all variants)

Figure: Logical model of synchronization reference selection on 7210 SAS shows a logical model of synchronization reference selection for the platforms, and Table: Synchronization options for 7210 SAS platforms provides a list of supported interfaces for each platform.

Figure: Logical model of synchronization reference selection on 7210 SAS

On the 7210 SAS-Mxp, 7210 SAS-R6, 7210 SAS-R12, and 7210 SAS-T, in addition to PTP and SyncE references, the recovered clock can be configured to derive the timing (frequency reference) from the BITS interface.

When quality Level (QL) selection mode is disabled, the reversion setting controls when the central clock can reselect a previously failed reference.

The following table lists the selection followed for two references in both revertive and non-revertive modes.