Timing Synchronization - Cisco ONS 15454 DWDM Reference Manual

8.7.8 Timing Synchronization

The MXP_2.5G_10E card performs ODU to OTU multiplexing as defined in ITU-T G.709. The ODU is
the framing structure and byte definition (ITU-T G.709 digital wrapper) used to define the data payload
coming into one of the SONET/SDH client interfaces on MXP_2.5G_10E. The term ODU1 refers to an
ODU that operates at 2.5-Gbps line rate. On the MXP_2.5G_10E, there are four client interfaces that can
be defined using ODU1 framing structure and format by asserting a ITU-T G.709 digital wrapper.
The output of the muxponder is a single 10-Gbps DWDM trunk interface defined using OTU2. It is
within the OTU2 framing structure that FEC or E-FEC information is appended to enable error checking
and correction.
8.7.8 Timing Synchronization
The MXP_2.5G_10E card is synchronized to the TCC2/TCC2P clock during normal conditions and
transmits the ITU-T G.709 frame using this clock. No holdover function is implemented. If neither
TCC2/TCC2P clock is available, the MXP_2.5G_10E switches automatically (hitless) to the first of the
four valid client clocks with no time restriction as to how long it can run on this clock. The
MXP_2.5G_10E continues to monitor the TCC2/TCC2P card. If a TCC2/TCC2P card is restored to
working order, the MXP_2.5G_10E reverts to the normal working mode of running from the
TCC2/TCC2P clock. If there is no valid TCC2/TCC2P clock and all of the client channels become
invalid, the card waits (no valid frames processed) until one of the TCC2/TCC2P cards supplies a valid
clock. In addition, the card is allowed to select the recovered clock from one active and valid client
channel and supply that clock to the TCC2/TCC2P card.
8.7.9 Enhanced FEC (E-FEC) Capability
The MXP_2.5G_10E can configure the FEC in three modes: NO FEC, FEC, and E-FEC. The output bit
rate is always 10.7092 Gbps as defined in ITU-T G.709, but the error coding performance can be
provisioned as follows:
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•
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8.7.10 FEC and E-FEC Modes
As client side traffic passes through the MXP_2.5G_10E card, it can be digitally wrapped using FEC
mode error correction or E-FEC mode error correction (or no error correction at all). The FEC mode
setting provides a lower level of error detection and correction than the E-FEC mode setting of the card.
As a result, using E-FEC mode allows higher sensitivity (lower OSNR) with a lower BER than FEC
mode. E-FEC enables longer distance trunk-side transmission than with FEC.
The E-FEC feature is one of three basic modes of FEC operation. FEC can be turned off, FEC can be
turned on, or E-FEC can be turned on to provide greater range and lower BER. The default mode is FEC
on and E-FEC off. E-FEC is provisioned using CTC.
Cisco ONS 15454 DWDM Reference Manual, R8.5
8-32
NO FEC—No FEC
FEC—Standard ITU-T G.975 Reed-Solomon algorithm
E-FEC—Standard ITU-T G.975.1 I.7, two orthogonally concatenated BCH super FEC code. This
FEC scheme contains three parameterizations of the same scheme of two orthogonally interleaved
BCH. The constructed code is decoded iteratively to achieve the expected performance.
Chapter 8 Transponder and Muxponder Cards
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