Name in the cause table
Non-EPS authentication unacceptable
Source: 3GPP TS 24.301 V20.1.0, clause 9.9.3.9, table 9.9.3.9.1. © 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TSDSI, TTA, TTC). Official text: 24301-k10.zip in the 3GPP archive.
3GPP Scout / Reference / EMM causes / EMM cause #26
TS 24.301EMM cause
EMM cause #26: Non-EPS authentication unacceptable
In plain words
The UE sends this cause to the network in S1 mode if the separation bit in the AMF field of AUTN is set to 0 in the AUTHENTICATION REQUEST message.
Our summary of the spec text quoted below.
What the spec says
When it is used
This EMM cause is sent to the network in S1 mode if the "separation bit" in the AMF field of AUTN is set to 0 in the AUTHENTICATION REQUEST message (see 3GPP TS 33.401 [19]).
Source: 3GPP TS 24.301 V20.1.0, clause A.3. © 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TSDSI, TTA, TTC). Official text: 24301-k10.zip in the 3GPP archive.
Same cause in 5GS (TS 24.501)
TS 24.501 defines the corresponding cause for 5GS. Its page quotes the 5GS wording.
- 5GMM cause #26 (TS 24.501)
How this page was made
3GPP Scout built this page from TS 24.301 V20.1.0 as indexed on 2026-10-15. The quotes are copied from the spec, and code checks each one against the stored text and the 3GPP archive file before publishing. The plain-words line was written by an AI model (GPT-6 Sol) and checked against the quotes by a second AI model from another company (Claude Opus 5.5). The official 3GPP text governs.