5.12 Overall Design Considerations 347 Note from Figure 5.34 that the NRZ system is not sensitive to the excess local chromatic dispersion. This is because the NRZ system essentially operates in the linear regime. Note also that the DM soliton system can achieve considerably higher transmission distances than NRZ and RZ systems for all values of the excess anoma- lous chromatic dispersion. Thus, DM soliton systems are superior to these systems over virtually all kinds of dispersion-managed fiber spans. We saw in Section 5.7.4 that (unchirped) RZ systems have a smaller PMD penalty than NRZ systems. Chirped RZ, or DM soliton systems, have an even smaller PMD penalty and thus are more suitable for transmission rates of 40 Gb/s and above, from the PMD perspective as well. 5.12 Overall Design Considerations We have seen that there is an interplay of many different effects that influence the system design parameters. We will summarize some of these effects in this section. In addition, two key issues in this regard, (1) the trade-off between higher bit rates per channel versus more channels, and (2) whether to use bidirectional or unidirectional