The ITU-T V-Series Recommendations on Data communication over the telephone network specify the protocols that govern approved modem communication standards and interfaces.
[1] Note: the bis and ter suffixes are ITU-T standard designators of successive iterations of a standard (bis and ter are the Latin words for "twice" and "thrice").
Applies to V.1–V.9 Applies to V.10–V.34 In order to gain first-mover advantage, many modem companies introduced models based on upcoming V-series standards before they reached final ratification.
In other cases, companies introduced non-standard systems but gave them ITU-like names.
Applies to V.35–V.39 Applies to V.40–V.49 Applies to V.60–V.99 Applies to V.100–V.199 Applies to V.200–V.249 Applies to V.250–V.299 Applies to V.300–V.399