G.657 is an international standard developed by the Standardization Sector of the International Telecommunication Union (ITU-T) that specifies single-mode optical fiber (SMF) cable. History The G.657 Recommendation builds on a previous fiber optic specification in G.652. G.657 was first published in 2006. Revisions of the standard were since published in 2009, 2012, and 2016 (November). References ITU-T recommendations ITU-T G Series Recommendations