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X.21

ITU-T telecommunications interface specification
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X.21

Summary

X.21 is an ITU-T Recommendation[1]. X.21 draws 13 Wikipedia views per month (itu_t_recommendation category, ranking #13 of 35).[2]

Key Facts

  • X.21's image is recorded as X21-15pin-D-Sub-connector-0a.jpg[3].
  • X.21's instance of is recorded as ITU-T Recommendation[4].
  • X.21's Commons category is recorded as ITU X.21[5].
  • X.21's Freebase ID is recorded as /m/02_j2p[6].
  • X.21's has edition or translation is recorded as Recommendation X.21 (11/1988): Interface between data terminal equipment (DTE) and data circuit-terminating equipment (DCE) for synchronous operation on public data networks[7].
  • X.21's ITU/ISO/IEC object ID is recorded as 0.0.24.21[8].
  • X.21's ITU-T Recommendation is recorded as X.21[9].
  • X.21's Microsoft Academic ID is recorded as 2779407552[10].
  • X.21's FOLDOC ID is recorded as X.21[11].

Why It Matters

X.21 draws 13 Wikipedia views per month (itu_t_recommendation category, ranking #13 of 35).[2] X.21 has Wikipedia articles in 6 language editions, a strong signal of global cultural recognition.[12]

References

Programmatic citations — every numbered marker resolves to a verifiable graph row below.

Direct Wikidata claims

  1. [3] ↑ . wikidata.org.
  2. [4] ↑ . wikidata.org.
  3. [5] ↑ . wikidata.org.
  4. [6] ↑ . Freebase Data Dumps. wikidata.org.
  5. [7] ↑ . wikidata.org.
  6. [8] ↑ . wikidata.org.
  7. [9] ↑ . wikidata.org.
  8. [10] ↑ . wikidata.org.
  9. [11] ↑ . wikidata.org.

Class ancestry

  1. [1] ↑ . Wikidata. wikidata.org.

Aggregate / graph-position facts

  1. [2] ↑ . Wikimedia Foundation. dumps.wikimedia.org.
  2. [12] ↑ . Wikidata sitelinks. wikidata.org.

📑 Cite this page

Use these citations when quoting this entity in research, articles, AI prompts, or wherever provenance matters. We aggregate Wikidata + Wikipedia + authoritative open-data sources; the stitched, scored, cross-referenced view is what 4ort.xyz contributes.

APA 4ort.xyz Knowledge Graph. (2026). X.21. Retrieved May 3, 2026, from https://4ort.xyz/entity/x-21
MLA “X.21.” 4ort.xyz Knowledge Graph, 4ort.xyz, 3 May. 2026, https://4ort.xyz/entity/x-21.
BibTeX @misc{4ortxyz_x-21_2026, author = {{4ort.xyz Knowledge Graph}}, title = {{X.21}}, year = {2026}, url = {https://4ort.xyz/entity/x-21}, note = {Accessed: 2026-05-03}}
LLM prompt According to 4ort.xyz Knowledge Graph (aggregator of Wikidata, Wikipedia, and authoritative open-data sources): X.21 — https://4ort.xyz/entity/x-21 (retrieved 2026-05-03)

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