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CWDM Gets a Boost

The International Telecommunication Union's Standardization Sector (ITU-T) has given the nod to a standard for CWDM gear that will help vendors' devices play nicey-nice.

The standard, ITU-T Recommendation G.695, describes signal attenuation, power levels, distance, interface speed, and other characteristics for coarse wavelength-division multiplexing. CWDM is a cheaper alternative to DWDM (dense Wavelength Division Multiplexing (WDM)) that's increasingly used to transport traffic in metro networks, including Ethernet data and SAN traffic (see CWDM: Low-Cost Capacity).

The significance, say industry sources, is that vendors that want their CWDM-based equipment to work together don't have to engineer their own interfaces to do so.

The new specs also add a 1.25-Gbit/s version for CWDM channels, which formerly were a standard 2.5 Gbit/s. This allows for devices that don't need the top rate -- gigabit Ethernet transponders, for example -- to be made and sold more cheaply.

Until now, there have been no standard interfaces between CWDM-enabled devices, and vendors wishing to create 1.25-Gbit/s CWDM links, usually for Gigabit Ethernet connectivity, haven't had an international standard to point to. Standards are important to carriers worldwide, so not having guaranteed interoperability among interfaces for metro services was seen as a hindrance by equipment suppliers (see CWDM Products Proliferate).

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