Name in the cause table
MAC failure
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 causes #20 and #21
TS 24.301EMM cause
EMM causes #20 and #21: MAC failure and Synch failure
Covers
TS 24.301 words these values in parallel, so they share this page. Each has its own section with the spec text and a plain explanation.
EMM cause #20: MAC failure
In plain words
The UE sends this cause to the network if the USIM detects that the MAC in the AUTHENTICATION REQUEST message is not fresh.
Our summary of the spec text quoted below.
When it is used
This EMM cause is sent to the network if the USIM detects that the MAC in the AUTHENTICATION REQUEST message is not fresh (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.
EMM cause #21: Synch failure
In plain words
The UE sends this cause to the network if the USIM detects that the SQN in the AUTHENTICATION REQUEST message is out of range.
Our summary of the spec text quoted below.
Name in the cause table
Synch failure
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.
When it is used
This EMM cause is sent to the network if the USIM detects that the SQN in the AUTHENTICATION REQUEST message is out of range (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 causes in 5GS (TS 24.501)
TS 24.501 defines the corresponding causes for 5GS. Their pages quote the 5GS wording.
- 5GMM cause #20 (TS 24.501)
- 5GMM cause #21 (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 lines were 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.