Specifications

Long-Distance Optical Transceivers
52 Continuous Access and Data Replication Manager SAN Extensions Reference Guide
Performance considerations
The very-long-distance optical transceiver extends the distance between the Fibre
Channel switch E_ports. Using credit-based flow control, the credit given to the
E_port is eight buffer-to-buffer (bb) credits, and Figure 14 shows how throughput
with these credits diminishes over distance. (This loss applies to any transmission
media, whether you are using long-distance transceivers, IP, ATM, or WDM.)
With both WDM and long-distance transceivers you can increase the performance
by increasing the buffer-to-buffer credits in the Fibre Channel switches. By
increasing the buffer-to-buffer credits to 48 bb the performance at 180 km will be
close to the same as that obtained using a 500-meter fiber.
Figure 14: Effects of distance on throughput with various buffer-to-buffer credits