Synchronization

Overview

The embedded Stratum 3 Timing Generator meets the specifications of GR-253-CORE, SONET Transport Systems Generic Criteria. The timing generator function is embedded in the 1x1 protected optical interface circuit packs in the main slot pair.

Timing modes

The timing generator supports four timing modes:

• External timing

  Locked to an external Stratum 3 (±4.6 ppm) or better DS1/E1 reference.

• Line timing

  Locked to recovered clock from an OC-N signal (from Main or tributary OC-3/OC-12/OC-48/OC-192).

• Free running

  Timing derived from high-stability temperature-compensated voltage-controlled crystal oscillator (TCVCXO) with a long-term accuracy of ±4.6 ppm and temperature stability of −40º C to +65ºC.

• Holdover

  Timing derived from the internal oscillator in the case of an unprotected synchronization reference failure. In this instance, the Stratum Timing Generator switches to "holdover mode" and continues to provide system timing, using the internal oscillator to maintain the last known good reference frequency. If the DS1/E1 timing output is enabled for network synchronization, DS1/E1 AIS will be inserted on detection of unprotected optical reference failure. In holdover mode, the accuracy is ±.37 ppm over the full −40°C to +65ºC temperature range.

• DS1/E1 timing outputs

  In addition, each timing generator (main circuit pack) provides a single DS1 or E1 sync output derived from a received optical interface signal (OC-N). These DS1/E1 timing outputs may be used to provide a timing reference signal to a local BITS clock For more information, see Chapter 5, Operations, administration, maintenance, and provisioning.

DS1 timing functions

The DS1 timing reference inputs and outputs meet the specifications of GR-499-CORE for DS1 interfaces and GR-253-CORE for timing references. The following are the DS1 timing functions:

• Two DS1 timing reference inputs

• Two DS1 timing reference outputs

• Alarms (Out of Frame, AIS, BER).

E1 timing functions

The E1 timing reference inputs and outputs meet the specifications of ITU-T G.813 for frequency accuracy, pull-in, hold-in and pull-out ranges, wander, jitter, noise tolerance, noise transfer, transient response and holdover performance. E1 references also comply with ITU-T G.704 standards for SDN SSM. The following are the E1 timing functions:

• Two E1 timing reference inputs

• Two E1 timing reference outputs

• Alarms (Out of Frame, AIS, BER).