Special Report: Next Generation Internet Applications
4.0 CURRENT DEPLOYMENT STRATEGIES
There have been many notable advances in photonic networks. Researchers have demonstrated DWDMs over 1000 channels. Optical transmission rates of OC-192 per DWDM channel are common. Total DWDM rates of ten terabits per second (Tbps) and transmission distances of up to 3,000 miles using EDFAs are possible. It is therefore possible in the near term to leverage the installed fiber optic cable base with DWDM, thereby creating 100-fold or even 1000-fold increases in transmission capacity with no new investment in fiber infrastructure. Photonic network capacity is doubling every nine months.[9] By comparison, electronic data processing and switching electronics are doubling in capacity every two years. There is great incentive to move switching into the optical domain where hopefully switching capacity can scale upward in proportion to transmission capacity. However, advances in photonic components are currently rudimentary in comparison to the state of electronics.
Advances in photonic packet switching have not made a major impact upon commercial network deployments. Photonic packet switching or circuit switching is possible using crude techniques that are slow and have unproven reliability.[27] Optical buffering techniques and optical storage is possible only under specially crafted laboratory conditions. Current light switching techniques are suitable for provisioning, but it will be from five to ten years before commercially viable, high-speed optical switching techniques appear.[9]
Kuwahara et. al. forecast the introduction of photonic products along a time line described in Table 4. As can be seen in the last row of the table, only DWDM and OADM are readily available for use in high capacity core networks. In the absence of OXCs, SONET equipment provides add and drop functions between adjoining DWDM networks. If the predictions of Table 4 hold true, then dynamic OADM and OXC systems will outstrip the bandwidth capacity of SONET equipment and thus displace SONET from core networks.
Optical core networks are evolving along the timeline shown in Table 4. Optical packet switching technology will not make major inroads into networks until issues of speed, reliability, conformance to standards, large-scale integration, and automated manufacturing are addressed by the communications industry. In the meantime, ATM switches and IP routers will provide the primary mechanisms for dynamic routing of traffic through high capacity core networks.
For the next five years or until all-optical packet switching is viable, electronic ATM and IP routers will dominate the switching layer, also called the "data link layer," of high capacity networks. High capacity electronic switching will bridge adjoining physical layers comprised of reconfigurable optical networks.
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