3GPP Scout / Reference / EPS NAS timers / T3421

TS 24.301NAS timer

Timer T3421: EPS mobility management, UE side

TS 24.301 V20.1.0Clause 10.2Table 10.2.1Checked 2026-10-15

In plain words

The UE starts T3421 after sending DETACH REQUEST without switch off indicated in the Detach type IE, and retransmits DETACH REQUEST when it expires.

Our summary of the spec text quoted below.

What the spec says

Timer value

15s NOTE 7 NOTE 8 In WB-S1/CE mode, 45s 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

DETACH REQUEST sent with the Detach type IE not indicating "switch off"

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

DETACH ACCEPT received

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

Retransmission of DETACH REQUEST

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.

State

EMM-DEREGISTERED-INITIATED EMM- REGISTERED. IMSI-DETACH- INITIATED

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.

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.