Description
Extended Emergency Number List Validity (EENLV) is a feature defined in 3GPP specifications that manages the UE's (User Equipment's) internal cache of emergency service numbers. The UE typically receives an 'Emergency Number List' from the network via NAS (Non-Access Stratum) signaling, which contains the dialing codes (e.g., 112, 911, 999) valid in its current location or registered PLMN. This list has a finite validity timer. EENLV extends the operational logic for this timer to ensure the UE can still attempt emergency calls using a potentially outdated list if it cannot reach the network to obtain a fresh one.
Architecturally, EENLV is implemented within the UE's NAS layer, specifically in the Mobility Management (MM) and Connection Management (CM) sublayers that handle subscriber registration and session management. The feature interacts with the UE's internal storage (often a USIM application or secure memory) where the last received Emergency Number List and its associated validity timer are kept. The core network indicates the list's validity duration, but with EENLV, the UE applies extended rules for using an expired list.
Operationally, when the UE needs to place an emergency call, it first checks its stored Emergency Number List. If the list's validity timer has expired, standard behavior might prevent the call attempt. With EENLV enabled, the UE is permitted to use the expired list under specific conditions, primarily when it is in a state where it cannot successfully perform a registration or location update to acquire a new list—such as in limited service state (e.g., out of coverage of its home network but within range of any available cell). The UE uses the last known valid list to interpret the dialed digits.
This mechanism is crucial for the UE's fallback logic. It ensures that the human-centric emergency service access is prioritized over strict protocol adherence to timers. The network can control the feature's parameters, but the UE's autonomous decision-making during failure scenarios is enhanced. EENLV does not modify the network-side procedures; it is a UE-centric reliability enhancement for emergency service discovery.
Purpose & Motivation
EENLV was introduced to solve a critical reliability gap in emergency calling. Prior to its introduction, if a UE's stored Emergency Number List expired and the UE could not contact a network to refresh it (e.g., due to being out of coverage, in a radio failure state, or in a non-allowed PLMN), the UE might not recognize a dialed emergency number. This could prevent the emergency call attempt altogether, creating a dangerous scenario where a user in distress cannot even attempt to connect to any available radio access.
The historical context is the increasing reliance on network-provided configuration for services, including emergency numbers which vary by country and region. While this dynamism is beneficial, it introduced a dependency: a UE without recent network contact might have an invalid view of emergency codes. EENLV addresses this by allowing the UE to use its last-known configuration as a best-effort fallback, prioritizing the ability to attempt a call over the certainty of number validity. This aligns with regulatory and safety principles that emergency access should be maximally available.
The feature mitigates the limitations of a strictly timer-driven approach. It acknowledges that in many emergency scenarios, the user's location or network conditions may be impaired. By extending the validity logic, it reduces the risk of a false negative where a UE incorrectly decides an emergency number is invalid. It complements other reliability features like support for emergency calls in limited service state and emergency bearer services.
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (66 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the Extended Emergency Number List (EENL) function was introduced, enabling the network to provide UEs with a list that includes extended and local emergency numbers, along with their applicable domains for call initiation. This release defined the storage mechanism for this list in the UE and specified the procedures for passing the Extended Emergency Number List to the upper layers for emergency number detection. Additionally, it included corrections to ensure the list is correctly handled and deleted upon PLMN change.
- Emergency numbers list with URN formats TS 24.301CR2998
- Extended and local emergency numbers and applicable domain for call initiation TS 24.301CR3012
- Storage of extended local emergency numbers TS 24.301CR3013
- Extended Emergency Number List IE TS 24.301CR3033
- Extended EMM cause for NB-IoT TS 24.301CR3035
- Handling of timer expiry during extended service request procedure for MT CSFB TS 24.301CR2900
+ 18 more changes
In Release 16, the EENLV function was enhanced to improve the continuity and handling of emergency sessions, particularly for UEs attached for emergency bearer services or RLOS access. Key corrections addressed UE behavior during system fallback scenarios, such as ensuring proper emergency call handling when a UE is attached for EPS services only or cannot attempt a PS emergency call after fallback. The release also introduced support for maintaining emergency session continuity upon attach failure and included corrections to the length of the extended emergency number list information element.
- UE attached for access to RLOS and emergency call TS 24.301CR3199
- Correct emergency CSFB for UE's performing system fallback TS 24.301CR3224
- Correct emergency call handling if UE is attached for EPS services only TS 24.301CR3233
- Correct emergency call handling when UE selected PS domain and after emergency service fallback the UE cannot attempt the PS emergency call TS 24.301CR3275
- Correct UE behavior when maximum number of active EPS bearer contexts is reached and the upper layers request more DRBs TS 24.301CR3317
- Detach before attach for RLOS and Emergency TS 24.301CR3338
+ 7 more changes
In Release 17, the EENLV function was enhanced to ensure a UE does not release its NAS signalling connection or indicate paging restriction during a Tracking Area Update procedure if an emergency service is ongoing in EPS. This prevents the interruption of emergency bearer services during mobility. Additionally, clarifications were made to improve the definitions of "PDN connection for emergency bearer services" and "Emergency EPS bearer context" for consistency.
- The MUSIM capable UE shall not initiate Service Request procedure for Leaving the network if Emergency service is ongoing TS 24.301CR3521
- Addition of extended NAS timers via a satellite access TS 24.301CR3687
- Failure to transfer emergency session upon successful attach TS 24.301CR3426
- Congestion handling of initial registration for emergency TS 24.301CR3461
- Correct the wrong timer number TS 24.301CR3493
- Fix typo in the minimum range of APN-AMBR for downlink or uplink (extended-2) TS 24.301CR3525
+ 9 more changes
In Release 18, the EENLV function was enhanced with new procedures for handling UE and network behaviour during transitions between N1 and S1 modes when only an emergency session is active, and for managing collisions between mobility management procedures like Tracking Area Update and network-initiated detach during emergency services. The release also specified rules for the storage of the EMM context when a UE is emergency attached and defined network handling for authentication reject messages received during emergency services.
- UE behaviour upon N1 to S1 transition with only Emergency session active TS 24.301CR3965
- Collision of TAU or SR for emergency service and network initiated detach TS 24.301CR3906
- EMM context storage when emergency attached TS 24.301CR3908
- Handling authentication reject during emergency services TS 24.301CR3962
- EMM context storage when emergency attached, 24.501 alignment TS 24.301CR3958
- Moving the NAS timer handling from the general section to Extended DC section TS 24.301CR4008
+ 1 more changes
In Release 19, the EENLV function was enhanced to improve network handling of emergency services, particularly for UEs maintaining a PDN connection for emergency bearer services after a disaster condition ends. The release introduced specific interactions for IMS emergency services in the eCALL-INACTIVE state and defined procedures for PSAP emergency callbacks with UEs in Power Saving Mode (PSM). It also clarified the handling of Forbidden TAI lists and addressed the persistence of Forbidden PLMNs in the Equivalent PLMN list following the release of an emergency PDN connection.
- MME behaviour when the disaster condition has ended and the UE maintains a PDN connection for emergency bearer services TS 24.301CR4572
- IMS emergency services in eCALL-INACTIVE state TS 24.301CR4164
- FTAI list handling for extended EMM cause with cause #15 TS 24.301CR4255
- PSAP emergency callback interaction with PSM TS 24.301CR4449
- Access barring for disaster roaming in case of emergency call TS 24.301CR4613
- Minor correction in reference number TS 24.301CR4648
+ 1 more changes
Explore further
Broader topics and technologies where EENLV plays a role.
Defining Specifications
3GPP specifications that define or reference EENLV, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 24.301 vj60 | NAS protocol for Evolved Packet System | Rel-19 |