---
oid: "0"
asn1-notation: "{itu-t(0)}"
description: "International Telecommunication Union - Telecommunication standardization sector (ITU-T)"
last-modified: "2026-04-30"
tags: [oid-repository]
---

## OID: `0` (last updated: 2026-04-30)

```asn1
{itu-t(0)}
```

"itu-t" is a standardized identifier, i.e., it may be used without its associated number in the ASN.1 notation.

Other identifiers that can be used in the last arc of the ASN.1 notation: `ccitt`, `itu-r`

### Description

International Telecommunication Union - Telecommunication standardization sector (ITU-T)

### Supplementary information

Subsequent OIDs identify ITU-T Recommendations (not jointly published with ISO/IEC) and ITU members. 
 
This OID is also called `ccitt(0)` to recall that CCITT used to be an organization independent of ITU-T. 
 
Identifier `itu-r` was added by ITU-T Study Group 17 in March 2004 (and was ratified by ISO/IEC JTC 1/SC 6 in Sep 2005). It can only be used as a 'NameAndNumberForm' (that is, followed by number `5` between parentheses) for OIDs that commence with [`{itu-r(0) r-recommendation(5)}`](https://oid-base.com/get-md/0.5) (see [Rec. ITU-T X.680 | ISO/IEC 9834-1](https://itu.int/rec/T-REC-X.680/en), clause A.5, for more details on this specific case). Consequently Unicode label "`ITU-R`" can only be used for "[OID-IRIs](https://oid-base.com/faq.htm#iri)" that designate OIDs under [`{itu-r(0) r-recommendation(5)}`](https://oid-base.com/get-md/0.5). 
 
Operation is in accordance with [Rec. ITU-T X.660 | ISO/IEC 9834-1](https://itu.int/rec/T-REC-X.660/en) and is under the guidance of [ITU-T Study Group 17](https://itu.int/ITU-T/studygroups/com17/index.asp). 
 
All decisions related to subsequent OIDs, other than the assignment of additional secondary identifiers to top-level OID `0` (see Rec. ITU-T X.660 \| ISO/IEC 9834-1, clause A.5), will be recorded as amendments to Rec. ITU-T X.660 \| ISO/IEC 9834-1 (such changes to the joint ITU-T \| ISO/IEC text will be regarded as editorial by ISO). 
 
From Rec. ITU-T X.660 \| ISO/IEC 9834-1, "the top-level arcs are restricted to three arcs numbered `0` to `2`; and the arcs beneath root arcs `0` and `1` are restricted to forty arcs numbered `0` to `39`. This enables optimized encodings to be used in which the values of the top two arcs for all arcs under top-level arcs `0` and `1` encode in a single octet in an object identifier encoding (see the Rec. ITU-T X.690 series \| ISO/IEC 8825 multi-part Standard)."

### Registrant

Name: ITU-T Study Group 17

### Child OIDs

- `0.0`: `recommendation(0)`
- `0.1`: `question(1)`
- `0.2`: `administration(2)`
- `0.3`: `network-operator(3)`
- `0.4`: `identified-organization(4)`
- `0.5`: `r-recommendation(5)`
- `0.9`: `data(9)`

This is a [frozen OID](https://oid-base.com/faq.htm#leaf) (no more child OIDs can be added to the existing ones).

### Terms of Use

[Terms of use](https://oid-base.com/disclaimer.htm.md)