Specifies the 37-pin and 9-pin connectors and the assignment of connector pin numbers at the interface between data terminal equipment (DTE) and data circuit-terminating equipment (DCE) where CCITT Recommendation V.2 4 together with Recommendations V.10 and V.11 are applicable. Use of the 9-pin connector only applies when a backward channel capability is implemented in an interface. This Standard is technically identical to ISO 4902:1980.