Although most early DWDM, OTM, and OADM
systems provided limited EMS/NMS support, newer offerings have much better capabilities.
Here a key requirement is ???end-to-end??? wavelength channel management,
which is generally complicated by the transparency of DWDM systems. Therefore, as
an interim solution, many vendors have adapted some form of SONET/SDH overhead
monitoring. Although this is usually only done at the edge or at select opaque (regeneration)
points inside ROADM/OXC networks, it still forces TDM framing of all client
data. Alternatively some vendors offer proprietary ???BER-agnostic??? optical-layer monitoring,
for example, laser powers, link powers, amplifier gain, and so on.
To better address wavelength monitoring concerns, the ITU-T OTN (G.872) has
standardized a ???digital wrapper??? solution for its optical payload unit (OPU) hierarchy.
Fiber and WDM 213
This standard combines channel-level OAM bytes with client-protocol agnostic payload
sections. These overhead features include performance monitoring, payload-independent
FEC, and reserved ring protection/restoration bytes. For example, sample FEC solutions
can deliver 2??“3 dB gain with about 6 percent bandwidth overhead??”a good improvement
[3].
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