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Optical Switching Systems and Technologies 133
Figure 6-4
The ONI
transport system
(ONI Systems)
Access Metro Core
Optical Ring
Optical Ring
The Need for Metropolitan DWDM Networks
The task of interconnecting SAN islands is one that is naturally
suited to optical networking. SONET/SDH-based network architec-
tures were designed for voice and private-line services (for example,
DS-1, DS-3) and cannot scale to support the gigabit channels
required for storage transport.These networks also cannot transport
storage data natively and in addition suffer from long provisioning
times.
The solution lies in the next-generation metropolitan DWDM net-
works that are being built out rapidly today. These networks meet
the requirements of metropolitan carriers for capacity, transparency,
scalability, dynamic provisioning, manageability, and survivability
for data-centric services at the lowest “first cost.” Next-generation
metropolitan DWDM networks, designed to offer wavelength ser-
vices, will enable service providers to leverage the existing network
infrastructure to offer SAN services and other user services (Fig-
ure 6-5).
Dynamic Optical Add-Drop Multiplexing
As the enterprise market evolves, Gigabit Ethernet and Fiber Chan-
nel will play increasingly important roles in all facets of metropoli-
tan optical networks. Metropolitan optical cross-connects can
provide dynamic reconfiguration of metropolitan enterprise net-
works, with optical layer survivability compatible with SONET
recoverability. In the reconfiguration/survivability scenario, optical