Timing Interface Features - Alcatel-Lucent 1643 AMS Applications And Planning Manual

Features

Timing interface features

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Synchronization Status Message (SSM) signal
A timing marker or synchronization status message signal can be used to transfer the
signal-quality level throughout a network. This will guarantee that all network elements
are always synchronized to the highest-quality clock that is available.
On the 1643 Access Multiplexer AM / 1643 Access Multiplexer Small AMS systems
the SSM algorithm or the timing marker is supported according to ITU-T
recommendation G.781 and ETSI recommendation ETS 300-417-6-1. The SSM is
supported on all STM-N interfaces.
Timing input
1643 Access Multiplexer AM / 1643 Access Multiplexer Small AMS do not support a
timing input.
2 Mbit/s and 1.5 Mbit/s tributary retiming
The user can choose whether individual 2 Mbit/s (E1 or X.21) or 1.5 Mbit/s tributary
outputs operate in "self-timed" or "re-synchronized" mode. In the (standard) self-timed
mode, the phase of the outgoing signal is a moving average of the phase of the
2 Mbit/s/1.5 Mbit/s signal because the signal is embedded in the VC-12 that is
disassembled. In the re-synchronized mode the 2 Mbit/s/1.5 Mbit/s signal is timed by
the SDH Equipment Clock (SEC) of the network element; frequency differences
between the local clock and the 2 Mbit/s/1.5 Mbit/s signal embedded in the VC-12 to
be disassembled are accommodated by a slip buffer.
There is also the following option: whenever the traceability of the local clock drops
below a certain threshold, the re-timing 2 Mbit/s/1.5 Mbit/s interfaces automatically
switch to self-timing. When this fail condition disappears, these interfaces return to
re-timing. These changes do not involve any hits in the traffic.
Important! Re-timing should only be applied when the network element which
performs the re-timing and the network element which generated the 2 Mbit/s or
1.5 Mbit/s signal have traced back their SECs to the same synchronization source.
Otherwise a continuous stream of 2 Mbit/s/1.5 Mbit/s frame slips or skips will
occur at the re-timing point which is indicated by a FCS threshold crossing alarm.
The user has the option of operating individual 2 Mbit/s or 1.5 Mbit/s outputs in
the "re-synchronized" mode. In this mode the 2 Mbit/s or 1.5 Mbit/s output signal
is timed by the system clock of the network element. However, when operating the
1643 Access Multiplexer AM / 1643 Access Multiplexer Small AMS with the
additional option card, jitter requirements for the 32nd port operating in this mode
may exceed ITU-T Recommendations G.783, G.813 (option 1), G.823 and G.825.
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2-22 Alcatel-Lucent - Proprietary
See notice on first page
365-312-801R7.2
Issue 3, May 2007