Page 725 - Introduction to Information Optics

12.4. Applications and Future Development of Optical Networks 709

actually work against each other to generate a stable, nondispersive pulse
which can be transmitted over very long distances. Solitons are more robust to
fiber polarization mode dispersion (PMD).

12.4.2, METROPOLITAN AND ACCESS NETWORKS

Access networks include networks connecting end users or customer prem-
ises equipment (CPE) to a local central office (CO). The metropolitan area
network (MAN) is responsible for connecting clusters of access networks to a
long-haul backbone network, also known as a wide-area network (WAN). The
long-haul market is focused largely on lowest cost per bit, whereas metro
networks focus on flexible, low-cost, service-oriented delivery of bandwidth.
Because metro networks serve a much larger number of clients, including
residential and business customers with varied needs, than long-haul networks,
network scalability and software-based automatic provisioning to reduce truck
roll for changes in network topology, bit rates, or customers are very crucial.
The overwhelming trend is to simplify network infrastructure by putting
more functions in new optical layers. One result of this evolution is that the
distinction between metro networks and access networks is blurring. Carriers
are building new metro networks to deliver service to CPE in the most direct
way possible.
New metro networks can be roughly cataloged as DWDM/router-based
networks and SONET-based networks. Figure 12.24 shows an example of a
DWDM/router-based network, in which bidirectional DWDMs couplers act
as passive optical splitters, dividing the light carried by the two OC-48s into

OC~1fl2

Fig. 12.24. DWDM router -based optical network.