Timer value
20s NOTE 7 NOTE 8 In WB-S1/CE mode, 38s NOTE 17
Source: 3GPP TS 24.301 V20.1.0, clause 10.2, table 10.2.1. © 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TSDSI, TTA, TTC). Official text: 24301-k10.zip in the 3GPP archive.
3GPP Scout / Reference / EPS NAS timers / Timers T3418 and T3420
TS 24.301NAS timer
Timers T3418 and T3420: AUTHENTICATION FAILURE sent by the UE
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.
Timer T3418: EPS mobility management, UE side
In plain words
The UE starts T3418 when it sends AUTHENTICATION FAILURE with EMM cause #20 or #26. On first expiry, the UE should consider the network false if not attached for emergency bearer services or access to RLOS.
Our summary of the spec text quoted below.
Started when
AUTHENTICATION FAILURE (EMM cause = #20 "MAC failure" or #26 "non-EPS authentication unacceptable") sent
Source: 3GPP TS 24.301 V20.1.0, clause 10.2, table 10.2.1. © 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TSDSI, TTA, TTC). Official text: 24301-k10.zip in the 3GPP archive.
On expiry
On first expiry, the UE should consider the network as false and follow item f of clause 5.4.2.7, if the UE is not attached for emergency bearer services or access to RLOS. [...]
Source: 3GPP TS 24.301 V20.1.0, clause 10.2, table 10.2.1. © 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TSDSI, TTA, TTC). Official text: 24301-k10.zip in the 3GPP archive.
Stopped when
AUTHENTICATION REQUEST received or AUTHENTICATION REJECT received or SECURITY MODE COMMAND received when entering EMM-IDLE mode indication of [...]
Source: 3GPP TS 24.301 V20.1.0, clause 10.2, table 10.2.1. © 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TSDSI, TTA, TTC). Official text: 24301-k10.zip in the 3GPP archive.
Timer T3420: EPS mobility management, UE side
In plain words
The UE starts T3420 when it sends AUTHENTICATION FAILURE with cause #21. On first expiry, the UE should consider the network false if not attached for emergency bearer services or access to RLOS.
Our summary of the spec text quoted below.
Timer value
15s NOTE 7 NOTE 8 In WB-S1/CE mode, 33s NOTE 17
Source: 3GPP TS 24.301 V20.1.0, clause 10.2, table 10.2.1. © 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TSDSI, TTA, TTC). Official text: 24301-k10.zip in the 3GPP archive.
Started when
AUTHENTICATION FAILURE (cause = #21 "synch failure") sent
Source: 3GPP TS 24.301 V20.1.0, clause 10.2, table 10.2.1. © 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TSDSI, TTA, TTC). Official text: 24301-k10.zip in the 3GPP archive.
On expiry
On first expiry, the UE should consider the network as false and follow item f of clause 5.4.2.7, if the UE is not attached for emergency bearer services or access to RLOS. [...]
Source: 3GPP TS 24.301 V20.1.0, clause 10.2, table 10.2.1. © 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TSDSI, TTA, TTC). Official text: 24301-k10.zip in the 3GPP archive.
Stopped when
AUTHENTICATION REQUEST received or AUTHENTICATION REJECT received or SECURITY MODE COMMAND received when entering EMM-IDLE mode indication of transmission failure of AUTHENTICATION FAILURE message [...]
Source: 3GPP TS 24.301 V20.1.0, clause 10.2, table 10.2.1. © 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TSDSI, TTA, TTC). Official text: 24301-k10.zip in the 3GPP archive.
Same timer in 5GS (TS 24.501)
TS 24.501 defines the corresponding timer for 5GS. Its page quotes the 5GS wording.
- T3520 (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.