.Part 4 SAN Extension and Bridging HP SAN Design Reference Guide 785354-001

For detailed information about distance rules for long-wave transceivers, see:
• “Fibre Channel distance rules for 16 Gb/s and 8 Gb/s switch models (B-series, C-series, and
H-series)” (page 157)
• “Fibre Channel distance rules for 4 Gb/s switch models (B-series and C-series switches)”
(page 158)
• “Fibre Channel distance rules for 2 Gb/s switch models (B-series and C-series switches)”
(page 159)
• “Fibre Channel distance rules for 1 Gb/s switch models (B-series and C-series switches)”
(page 159)
NOTE: To ensure adequate link performance, see “Extended fabric settings for Fibre Channel
switches” (page 264).
Wavelength division multiplexing
This section describes the following:
• “WDM overview” (page 261)
• “WDM network implementation” (page 261)
• “WDM system architectures” (page 262)
• “WDM system characteristics” (page 262)
• “HP coarse wave division multiplexing” (page 263)
• “Third-party WDM products” (page 263)
WDM overview
WDM devices extend the distance between two Fibre Channel switches. The devices are transparent
to the switches and do not count as an additional hop.
To accommodate WDM devices, you must have enough Fibre Channel BB_credits to maintain
line-speed performance. WDM supports Fibre Channel speeds of 4 Gb/s, 2 Gb/s, and 1 Gb/s.
When planning SAN extension, BB_credits are an important consideration in WDM network
configurations. Typical WDM implementations for storage replication include a primary and
secondary path. You must have enough BB_credits to cover the distances for both the primary path
and secondary path so that performance is not affected if the primary path fails.
WDM network implementation
WDM-based networks provide a lower-cost way to respond quickly to increased bandwidth
demands and protocol changes. The quick response occurs because each wavelength is a new,
full-bandwidth communications link. In many areas of the world, it is less expensive to deploy
WDM devices on existing fiber than it is to install new fiber.
After implementing WDM, service providers can establish a “grow as you go” infrastructure.
Service providers can expand capacity in any portion of their networks. Carriers can address
areas of congestion resulting from high-capacity demands.
WDM enables you to partition and maintain dedicated wavelengths for different customers. For
example, service providers can lease wavelengths (instead of an entire fiber) to their high-use
business customers.
Fibre Channel long-distance technology 261