HP StorageWorks 4000/6000/8000 .HP StorageWorks SAN Design Reference Guide, Pa - Page 284

• WDM system characteristics, page 285 • HP coarse wave division multiplexing, page 285 • Third-party WDM products, page 286 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. WDM system architectures The WDM system architectures are as follows: • Passive (optical transmission protocol) • Active signal amplification • Active protocol handling Most WDM products use one of these architectures or combine attributes of each. Table 140 summarizes the WDM system architectures. Table 140 WDM system architectures System architecture1 Description Passive (optical transmission protocol) • Transparent to transmission protocol and data-rate independent • Establishes open interfaces that provide flexibility to use Fibre Channel, SONET/SDH, ATM, Frame Relay, and other protocols over the same fiber • Passes the optical signal without any form of signal conditioning such as amplification or attenuation 284 SAN extension