Special Report: Next Generation Internet Applications
5.2 Photonic Network Management Network management is a necessary part of photonic networks. Failures within terabit-per-second optical networks will have devastating impacts on many applications. Therefore, photonic networks must protect against optical node and cable failures in a manner that assures high network reliability. Network management functions must include monitoring, provisioning, and restoration switching. Monitoring must detect changes in signal-to-noise ratios and wavelength deviations. Network management functions must appear within OADM and OXC equipment.
It is possible to configure DWDM networks into as many as eight different types of rings. Automatic protection system (APS) protocols must be added to these ring configurations for reliable protection and restoration functions to exist within the DWDM-based network.
A cohesive network management system will be needed to manage combinations of DWDM, SONET, IP, and ATM networks. Currently, SONET network management systems are proprietary, creating serious problems for the maintenance and operation of SONET rings when multiple suppliers are involved.
SONET benefits from its excellent protection and restoration features. Restoration times of 50 ms make SONET the standard by which all other multiplex technology reliability is judged.[3] DWDM has relatively long fault detection and restoration times when compared to SONET and ATM.
Yet, DWDM lies at a lower layer within the network than ATM and SONET. Reliable restoration requires that DWDM detect and restore faults much more quickly than the SONET and ATM layers. Otherwise, instabilities may develop when higher network layers attempt to restore faults that are subsequently corrected by the DWDM layer. Photonic switching times must be reduced as DWDM takes up larger portions of the physical network.
Optical switching is, therefore, a necessary part of a highly reliable photonic network. However, there are only a few available optical switching technologies (e.g., optical bubble, MEM, and liquid crystal array). Optical switching technologies lag their electronic counterparts by 25 years in terms of speed, fabrication, integration, and sophistication, putting them on the same par with medium-scale integrated electronics. Even so, the optical switching market is approximately $247 million with growth expectations to more than $2 billion by 2004. Service providers are expected to deploy optical cross connects during 2001.[46] Manufacturers of optical switching see demand for their equipment to provide optical add/drop multiplexing and protection switching.
Photonic switching technology must see greater standardization, larger scale integration, and automated fabrication before there will be full displacement of electronics in favor of all-optical networks.[47]
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