Nortel Networks OPTera Metro 3500 User Manual

Page 186

2-148 Operation, administration, and maintenance (OAM) features

OPTera Metro 3500 Multiservice Platform NTRN10AN Rel 12.1 Standard Iss 1 Apr 2004

Tributary line timing

Tributary line timing is shown in

, example d).

When using tributary line timing, a network element derives timing from a
received tributary signal. Possible sources of tributary line timing are OC-3,
OC-12, OC-48, DS1, and EC-1 facilities.

Note 1: Tributary line timing is derived from DS1 circuit pack
(NTN430AA, BA) provisioned in OPTera Metro 3500 shelf equipped with
VTX-series circuit packs. DS1 lining timing is not derived from the DSM
modules.

Note 2: Tributary line timing is derived from EC-1x3 (NTN436AA)
circuit pack.

When the network element timing mode is set to Line Timing (no distinction
is made between Transport or Tributary on the user interface), it selects one of
up to two provisioned timing sources (primary and secondary timing
references) as the active timing reference. This signal is used in network
elements to synchronize the outgoing transport signals in all directions, and the
synchronous tributaries terminated by the network element. The selection of
the best quality signal is made based on the stability of the transport signal, the
synchronization message, and any incoming synchronization status
provisioned by the user. For more information on synchronization messaging,
see

Synchronization-status messages on page 2-156

Table 2-30
Timing signal sources

Internal timing mode

VTX-48, VTX-48e or STX-192 circuit
pack

provide timing signals of ST3 quality

External timing mode

BITS In A

BITS In B

building-integrated timing supply (BITS)
provide a clock of ST3 quality or better

Line timing mode (transport / tributary)

OC-3

slots 3 through 10