# Recommendation Q.921 (11/1988): ISDN user-network interface - Data link layer specification

> superseded recommendation/international standard from the International Telecommunication Union

**Wikidata**: [Q26985444](https://www.wikidata.org/wiki/Q26985444)  
**Source**: https://4ort.xyz/entity/recommendation-q-921-11-1988-isdn-user-network-interface-data-link-layer-specification