# Recommendation X.30 (11/1988): Support of X.21, X.21 bis and X.20 bis based data terminal equipments (DTEs) by an integrated services digital network (ISDN)

> superseded recommendation/international standard from the International Telecommunication Union

**Wikidata**: [Q26985487](https://www.wikidata.org/wiki/Q26985487)  
**Source**: https://4ort.xyz/entity/recommendation-x-30-11-1988-support-of-x-21-x-21-bis-and-x-20-bis-based-data-terminal-equipments-dtes-by-an-integrated-services-digital-network-isdn-