HP StorageWorks 2/24 FW 07.00.00/HAFM SW 08.06.00 McDATA Products in a SAN Env - Page 185

Implementing SAN Internetworking Solutions 4 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 SDR 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. Implementing SAN Internetworking Solutions 4-41