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  • Standards Boost Fiber Optic Bandwidth
Nov 2003
GENEVA, Nov. 11 -- A United Nations-affiliated telecommunications group has approved two new standards that it says will increase bandwidth in fiber optic lines and reduce costs for network providers.

Recommendation G.959.1, developed by the Geneva-based International Telecommunication Union (ITU), allows a transmission speed of 40 Gb/s, up from a maximum of 10 Gb/s.

Moving to higher bit-rates will reduce the number of optical systems required in a network, the ITU said. "Historically," said Peter Wery, chairman of the ITU-T group responsible for the standard, "each fourfold increase in data speed has multiplied costs by just two and half times, leading to lower cost per bit. If this historical precedent holds true, 40 Gb/s technology will reduce systems equipment costs by up to 40 percent."

Standard G.695 applies to coarse wavelength division multiplexing (CWDM), used most often in metropolitan networks. ITU said it supports CWDM because it lets metropolitan fiber networks expand capacity more cheaply than the incumbent technology, dense wavelength division multiplexing (DWDM). CWDM is cheaper because it allows greater spacing between channels on a fiber optic line and can handle less-expensive "uncooled lasers." It said experts estimate that carriers with sufficient deployed fiber could save as much as 30 percent using a CWDM solution compared with the DWDM alternative.

Peter Wery, chairman of the starndard's study group, said, "CWDM systems have the flexibility to be deployed in point-to-point connections and in rings. Their suitability to carry Ethernet traffic and to interconnect storage area network islands make these systems of interest to large and medium-sized carriers, but also to cable TV companies and for enterprise network operators."

The ITS said 40 Gb/s systems covered by ITU-T G.959.1 can be installed on most existing ITU-T G.652, ITU-T G.653 and ITU-T G.655 optical fibers. However, to make the deployment of 40 Gb/s systems easier, ITU approved in January 2003 a revision of the Recommendations ITU-T G.652 and G.655, in order to include more stringent limits for polarization mode dispersion. Many new technologies are used in this standard, such as forward error correction techniques and adaptive chromatic dispersion compensators.

The G.695 standard applies to CWDM systems for optical networks from 40 km to 80 km long. The technology supports wavelengths between 1270 nm and 1610 nm and signal rates of 2.5 Gb/s and 1.25 Gb/s. Only 40 Gbit/s single-channel interfaces are standardized in the present version of ITU-T G.959.1.

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