ITU-T prepares for 40-Gbit/sec systems

March 1, 2004

ITU-T Study Group 15 on optical transport networks has recently issued a new version of Recommendation G.959.1, which increases the capacity for optical interfaces of optical transmission systems to 40 Gbits/sec.

Moving to higher bit rates reduces the number of optical systems required in a network, which in turn decreases the cost per bit of data carried and the costs of network maintenance and management. Moreover, it will allow optical systems to meet the requirements of high-capacity Internet routers already on the market.

G.959.1 provides physical layer interdomain interface (IrDI) specifications. The applications are defined to be "transversely compatible," which means the ends of an optical section can be terminated by a transmitter and receiver from different manufacturers. In other words, the Recommendation allows (among other things) an easy interface between two different network operators (interdomain interface) deploying equipment from different vendors.

The 40-Gbit/sec systems covered by G.959.1 can be installed on most existing G.652, G.653, and G.655 optical fibers. But to make the deployment of 40-Gbit/sec systems still easier, ITU-T approved more stringent limits on polarization-mode dispersion at its January 2003 meeting.

The standard has been developed to address the need for connecting network nodes placed at different distances. The new standard targets two un-amplified link distances: The first is for lengths up to 40 km and the second, up to 80 km. The new specifications are based on the results of extensive field trials between a number of service providers and manufacturers.

Whether using 3G, 4G, GSM, WLAN, or PSTN, chances are fiber optics will be somewhere in the network. For this reason, ITU-T is keen to continue to attract more participation to its work in these backbone technologies that will make next-generation networks work.

Houlin Zhao is director of the International Telecommunication Union's Telecom Standardization Bureau. For more information, contact Greg Jones at [email protected] visit