# X.21

> ITU-T telecommunications interface specification

**Wikidata**: [Q1424171](https://www.wikidata.org/wiki/Q1424171)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/X.21)  
**Source**: https://4ort.xyz/entity/x-21


## References

1. Freebase Data Dumps. 2013