Nortel Networks OPTera Metro 3500 - Manual (Page 196)

2-158 Operation, administration, and maintenance (OAM) features
OPTera Metro 3500 Multiservice Platform NTRN10AN Rel 12.1 Standard Iss 1 Apr 2004
User-specified quality levels for timing sources
A user can specify or override the quality level of an incoming timing source.
The user can specify the quality level if the timing source comes from
equipment that does not support SSM, such as a BITS or equipment from
another vendor. If a user specifies the quality level of a timing source, the user
interface appends “-P” to the quality level, for example, ST2-P. Avoid
overriding the quality level of an incoming tributary timing source if SSM is
supported, to avoid timing loops.
BITS output with VTX-series or STX-192 circuit packs
STX and VTX-series circuit packs provide 1+1 non-revertive timing reference
switching for BITS Out. When the BITS Out primary and the secondary
references fail,
an alarm indication signal (AIS) is sent by the network element
as BITS Out. The AIS advises equipment using the BITS Out of the failure so
they do not use the BITS Out for synchronization.
When DS1 ESF is provisioned, SSM is supported on BITS Out. The BITS Out
SSM is based on the status message from the active timing reference. BITS
Out always selects the best quality timing reference based on the SSM of the
incoming timing source.
User-initiated synchronization switches
Synchronization switching can take place under the control of the user. With
this capability, the user can select the optical interface to which a line-timed
network element synchronizes. The line-timed network element accepts the
user selected switch as long as the timing reference quality of both optical
interface is the same and not equal to DUS, RES, SMC, or ST4.
Synchronization switching in a UPSR, BLSR and 1+1 is non-revertive.
OPTera Metro 3500 supports the following synchronization modes:
• two SF/ESF formatted BITS inputs and outputs
• line timing over DS1, OC-n, and EC-1 facilities
• internal Stratum 3 timing
• synchronization status messaging for BITS input and output, and for
SONET facilities (OC-n)
• DS1 ESF BITS synchronization status messaging
Note 1: The DS1 service module (DSM) and the OC-3 interface connected
to a DSM cannot be used as a synchronization source.
Note 2: Line timing with the EC-1x12 circuit pack is not supported.