The ITU-T has approved new standards to mitigate ‘soft errors’ in terrestrial telecoms equipment caused by cosmic rays.
Unlike a hard error, which is a fault that causes permanent malfunctioning of a semiconductor device, a soft error is a temporary error that disappears as soon as the semiconductor device concerned is restarted or the data concerned are overwritten.
In recent years, the number of soft errors caused by cosmic radiation neutrons has been increasing gradually even in telecoms equipment located on the ground.
The soft error disappears as soon as the affected semiconductor device is restarted or the data are overwritten. Even though a soft error in data can cause a malfunction or system outage, it is difficult to reproduce such a transient error and identify the cause. Since a soft error can have a serious impact on the user, it is a major headache for system operators. Telecoms equipment is designed so that such malfunctions don’t affect network services. But because soft errors are difficult to reproduce, they are typically not sufficiently verified at the development stage.
Recently, however, it has become possible to measure the influence of soft errors on telecoms equipment using a compact accelerator-driven neutron source (a facility for producing neutrons through a nuclear reaction caused by irradiating the target with protons or electrons that are sped up by an accelerator).
This measurement makes it possible to determine the influence of soft errors and take preventive measures in advance before vendors sell products and telecommunication carriers introduce telecommunication equipment into operating networks.
While it has become possible for carriers to improve network quality dramatically by mitigating soft errors at the stages of equipment development and introduction, there is a need for requirements that serve as the benchmark for methods and evaluation of countermeasure.
ITU-T SG5 has approved recommendations to stipulate the design, testing and quality estimation methods and reliability requirements concerning soft errors. They include benchmarks based on which vendors and carriers can select measures against soft errors that are appropriate for the required reliability level.
The soft-error-related standards approved by ITU-T consist of five recommendations and a supplement, as detailed in the graphic below.
The standards are based on draft recommendations jointly developed by NTT, Fujitsu, Hitachi, NEC, and Oki, with the cooperation of Orange.