Nortel Networks NTRN10AN, 3500 Tributary line timing, Timing signal sources Internal timing mode

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

Tributary line timing

Tributary line timing is shown in Figure 2-49 on page 2-155, 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	provide timing signals of ST3 quality
pack
External timing mode
BITS In A	building-integrated timing supply (BITS)
BITS In B	provide a clock of ST3 quality or better
Line timing mode (transport / tributary)
OC-3	slots 3 through 10
OC-3x4	slots 3 through 10
OC-12	slots 3 through 12
OC-12x4 STS	slots 3 through 10 (see Note 1)
OC-48	slots 11 and 12 (see Note 2)
OC-48 STS	slots 3 through 12 (see Note 1)
OC-192	slots 11 and 12 (see Note 1)

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