Evolution of optical transport in the AT&T network

Summary form only given. Achievement of a physically diversified multiple vendor environment is desirable. Despite the ubiquity of SONET equipment, however, the absence of true mid-span meet in long-haul SONET optical transmission systems makes this a challenging objective and leads to an examination of the network transport architecture for other opportunities to facilitate a multiple vendor transport infrastructure environment. One such opportunity can be created by the separation of the optical and SONET layers through the use of optoelectronic converters (i.e., transponders) and the utilization of low-cost standardized optical interfaces. The resulting stand-alone WDM optical transmission systems can be connected directly to SONET equipment or other optical transmission equipment from different suppliers through a low-cost standardized interface. Furthermore, the introduction of transponders at the interfaces of WDM long haul line systems provides an effective vehicle for fault detection and localization, a medium for the gradual introduction of new transmission technologies, and a means to clean up the often significant transmission impairments that accumulate in long-haul systems without necessitating return to the SONET layer. Although increased equipment costs is a commonly voiced concern about the introduction of transponders, experience suggests that costs for transponders will continue to drop as applications increase.