Specifications

Wavelength Division Multiplexing
38 Continuous Access and Data Replication Manager SAN Extensions Reference Guide
Active protocol handling
While most WDM systems are designed to be protocol independent, products are
available that offer a system with protocol-specific capabilities for Fibre Channel.
This design enables digital time division multiplexing (TDM) on top of existing
optical multiplexing to support multiple channels per wavelength.
This design also allows for network monitoring, digital retiming (to reduce timing
jitter), link integrity monitoring, and distance buffering. Considering the added
sensitivity to protocols, this WDM variant seems straightforward in point-to-point
configurations but may require additional and potentially costly transmission
hardware when deployed in meshed networks.
System characteristics
Acceptable and optimal WDM systems have certain key characteristics. These
characteristics are recommended for any WDM system in order for carriers to
realize the full potential of this technology:
■ Use the full capacity of the customers’ existing dark fiber
■ Offer component reliability, 24x7 availability, and expandability
■ Provide optical signal amplification and attenuation. This is desirable on the
client side and long-haul side interfaces to increase the transmitted/received
signal-to-noise ratio.
■ Provide signal conditioning (that is, the retiming and reshaping of the optical
data-carrying signal) for optimization of the bit error rate
■ Offer channel add/drop capability (the ability to change the number of data
channels by adding or dropping optical wavelengths at any network node
location)
■ Allow compensation of power levels (preferably automatic or without manual
intervention), especially to facilitate adding (or dropping) channels
■ Provide upgradable channel capacity and/or bit rate.
■ Allow interoperability which requires standards-compliant interfaces such as
Fibre Channel, SONET, ATM, and so on
■ The wavelength at each customer’s interface channel is converted to a longer
wavelength prior to multiplexing with other channels for transmission over
the long haul.