# Recommendation I.431 (11/1988): Primary rate user-network interface - Layer 1 specification

> superseded recommendation/international standard from the International Telecommunication Union

**Wikidata**: [Q26985443](https://www.wikidata.org/wiki/Q26985443)  
**Source**: https://4ort.xyz/entity/recommendation-i-431-11-1988-primary-rate-user-network-interface-layer-1-specification