# Recommendation V.21 (11/1988): 300 bits per second duplex modem standardized for use in the general switched telephone network

> recommendation/international standard from the International Telecommunication Union

**Wikidata**: [Q27051495](https://www.wikidata.org/wiki/Q27051495)  
**Source**: https://4ort.xyz/entity/recommendation-v-21-11-1988-300-bits-per-second-duplex-modem-standardized-for-use-in-the-general-switched-telephone-network