be specified. The G.655 upper limit on PMD should be contrasted with the
tighter and more realistic requirements discussed in Section IV, because it
could be argued that PMD is the most critical specification for upgradeability
to 40-Gbps operation.
2
A final fiber category is the CWDM/DWDM optimized fibers outlined in
G.656. The original purpose of this category was to have low dispersion from
1460 to 1625 nm to decrease ISI that limits uncompensated CWDM transmis-
sion. However, the requirements evolved substantially during consideration and
debate. In the final analysis, G.656 can be considered to be the wideband
Raman-enabled fiber standard. These fibers have specified performance over
the 1460- to 1625-nm wavelength range (similar to the newer