# Recommendation G.704 (11/1988): Synchronous frame structures used at primary and secondary hierarchical levels

> superseded recommendation/international standard from the International Telecommunication Union

**Wikidata**: [Q27051356](https://www.wikidata.org/wiki/Q27051356)  
**Source**: https://4ort.xyz/entity/recommendation-g-704-11-1988-synchronous-frame-structures-used-at-primary-and-secondary-hierarchical-levels