Specifications

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Implementing SAN Internetworking Solutions
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Implementing SAN Internetworking Solutions
Light wavelengths used are typically around 1,550 nanometers (nm).
Optical fiber performs well in this wavelength region, with very little
attenuation. For CWDM, differing wavelengths are separated by
multiples of 20.0 nm. For DWDM, differing wavelengths are
separated by multiples of 0.8 nm. The lower wavelength numbers
provided by CWDM are due to lower accuracy (and price) of lasers.
DWDM wavelengths are spaced closer together and require more
precise lasers to reduce interference between wavelengths.
CWDM and DWDM are metropolitan extension technologies that
transmit data parallel-by-bit or serial-by-character over a fiber-optic
network. The signal is never terminated in the optical layer and is
therefore bit-rate and format independent. As a result, WDM
provides high bandwidth, low latency, and transparency to SAN
protocols and allows transmission of e-mail, voice, video,
multimedia, and digital data over native FCP or FICON links.
Figure 4-9 illustrates extended-distance connectivity through a WDM
interface.
Figure 4-9 WDM Extended-Distance Connectivity
When combined with a dedicated FCP or FICON link, the
technology:
• Is well suited as an extension technology for RDR/S applications
over metropolitan distances up to 75 miles (120 km). Note that
WDM technology does not increase the transmission distance
provided by repeated dark fiber. However, WDM significantly
increases the bandwidth.