Nortel Networks OPTera Metro 3500 - Manual (Page 187)

Operation, administration, and maintenance (OAM) features 2-149
Planning and Ordering Guide—Part 1 of 2 NTRN10AN Rel 12.1 Standard Iss 1 Apr 2004
The best timing reference source is a high-level stratum clock.
Timing modes
The four possible timing modes for OPTera Metro 3500 network elements are:
• Free run. See Free run mode on page 2-149 .
• Acquire. See Acquire mode on page 2-149 .
• Normal. See Normal mode on page 2-149 .
• Holdover. See Holdover mode on page 2-149 .
Free run mode
Free run mode is a target mode that can be provisioned by the user. In free run
mode, the voltage-controlled crystal oscillator (VCXO) clock in the module is
not locked to a timing reference and runs at its natural frequency. Network
elements with STX and VTX-series circuit packs provide timing references of
ST3 quality.
Acquire mode
Acquire mode is not a mode that the user can provision. Acquire mode is the
current mode when the VCXO clock in the module tracks a timing reference
and the timing-mode-maintenance software quickly brings the clock
frequency into approximate agreement with the timing reference frequency.
That reference may be the 8-kHz timing signal derived from an incoming
SONET signal, a DS1 signal, or BITS inputs. The signal format of the BITS
input can be set to DS1 or composite clock.
Normal mode
Normal mode is a mode that can be provisioned by the user. When this is the
current mode, the VCXO clock in the module locks to a timing reference.
Normal mode is used during trouble-free operations.
Holdover mode
Holdover mode is not a mode that the user can provision. The module enters
holdover mode automatically if the target mode is normal but all timing
references have become unavailable. If the module enters holdover mode, the
VCXO clock in the module holds within a certain frequency range of the last
locked-in timing reference. When a timing reference becomes available again,
DS1 slots 3 through 10 (see Note 2 )
EC-1x3 slots 3 through 10
Note 1: Requires STX-192 circuit packs provisioned in slots 13 and 14.
Note 2: Supported on shelved equipped with VTX-series circuit packs in slots 13
and 14.
Table 2-30 (continued)
Timing signal sources