Technical data

Release 5.0.x Turin Networks Page 8-1
8.1 Introduction
The TE-2020 system uses a hierarchical master-slave arrangement for synchronization to the network.
There are up to six (6) user selectable synchronization reference inputs from which the distributed clock
(timing reference) is selected. The system can select any of the following as either the primary timing ref-
erence or the secondary timing reference.
• Any SONET interface
• References provided from a BITS (Building Integrated Timing Supply)
• Internal
NOTE: In this context, reference to the term clock actually refers to the output of the Stratum-3 tim-
ing module, or effectively, the timing reference that is distributed (output) by the TE-2020.
The output of the TE-2020 synchronization takes on the same quality as the selected input reference. The
quality of the timing reference signal is characterized to be one of four levels, called Stratum levels. Stra-
tum 1 clocks are the most accurate, while Stratum 4 clocks are the least accurate. These levels have been
standardized and their basic performance parameters are defined in ANSI T1.101. The TE-2020 system,
when in holdover mode or free-run mode, provides and distributes a Stratum 3 timing reference. The TE-
2020 system distributes the clock reference(s) via one or more of the following facilities:
• Protected derived DS1 signals
• Any (or all) of the OC-n out-bound signals
Generally in a network, one node is selected as a reference source for all other nodes. The one node will
obtain a Stratum 1 reference from a BITS input and distribute the reference over the optical interfaces. The
adjacent nodes will select the incoming optical signal closest to the timing supply node as a primary refer-
ence. A Do Not Use for Sync (DUS) signal is generated in the SONET overhead from the receiving nodes
back to the originating adjacent timing reference node. This prevents the reference node from attempting to
obtain a reference signal from the adjacent nodes in the event of a BITS timing failure which would in turn
cause a timing loop. DUS is transmitted back on both fibers in protection groups. Refer to Figure 8-1