# Recommendation U.21 (11/1988): Operator recall on a telex call set up on a radiotelegraph circuit

> recommendation/international standard from the International Telecommunication Union

**Wikidata**: [Q27051471](https://www.wikidata.org/wiki/Q27051471)  
**Source**: https://4ort.xyz/entity/recommendation-u-21-11-1988-operator-recall-on-a-telex-call-set-up-on-a-radiotelegraph-circuit