Again, the former requirement is more tailored
for higher packet-switching layers as it pertains to individual end-user counts.
However, DWDM is very well-positioned with regards to the latter requirement
since current OTM and OADM systems can readily scale to support hundreds of
channels at gigabit-level speeds.
?– Reliability/protection The MEF standards also call for rapid service protection
at the end-to-end path level, with speeds matching 50 ms SONET/SDH timescales.
Additionally, the need for line and node level protection is also stated. Today, many
commercial WDM platforms are already fully network-equipment building systems
(NEBS)??“compliant and offer ???five nines??? (99.999 percent) availability??”under five
minutes annual downtime. Moreover, a full range of WDM survivability options are
available, most of which can match SONET/SDH timescales (see ???Optical Network
Architectures???). In fact, some dedicated schemes such at 1+1 span or UPSR path
protection can even achieve lower millisecond recovery (less than 10 ms).
?– TDM support This requirement mandates legacy TDM voice support via circuit
emulation (???pseudo-wire???).
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