Description
The Outgoing Call Timer (OCT) is a subscriber-specific timer stored within the Universal Subscriber Identity Module (USIM) application, as defined in 3GPP TS 31.102. It is a proactive UICC (Universal Integrated Circuit Card) feature, meaning the USIM can initiate actions independently of the Mobile Equipment (ME). The timer's primary function is to limit the duration of a mobile-originated call setup procedure. When a user initiates a call, the ME sends a SETUP message to the network. Concurrently, the USIM starts the OCT. If the call is successfully established (e.g., the user answers), the timer is stopped. However, if the call setup does not complete within the pre-configured OCT duration—due to network congestion, the called party not answering, or other failures—the USIM proactively commands the ME to terminate the call attempt. This is typically done by sending a terminal response with a specific result, such as 'Call control by USIM,' which instructs the ME to release the call.
The OCT value is a parameter defined in the USIM's Elementary File (EF) under the Telecom service table. It is configured by the operator and can be personalized for different subscribers or subscription plans. The timer mechanism is part of the Call Control (CC) service provided by the USIM, which interacts with the ME's call control layer via the Application Protocol Data Unit (APDU) interface defined by ETSI/3GPP. The USIM monitors the call state by processing envelope commands from the ME that carry call status information.
Architecturally, the OCT operates within the secure environment of the UICC, ensuring the timer logic and value are tamper-resistant. Its enforcement is independent of the network core, providing a reliable fallback mechanism even if network signaling experiences delays or anomalies. By imposing a finite time limit on call setup, the OCT helps prevent scenarios where a mobile device remains stuck in a prolonged call establishment state, which could drain battery, occupy radio resources unnecessarily, and lead to a poor user perception of service reliability. It is a fundamental element of the USIM's role in managing basic telephony services securely and efficiently.
Purpose & Motivation
The Outgoing Call Timer was introduced to address the problem of indefinite or excessively long call setup attempts in mobile networks. Prior to its standardization, if a call setup failed due to network issues or an unresponsive called party, the mobile device might remain in a call setup state for an unpredictable duration, waiting for a network response or timeout. This wasted valuable radio resources (like the traffic channel) and device battery life, and could cause user confusion as the device appeared to be 'stuck.' The OCT provides a standardized, subscriber-controlled mechanism to bound this time.
Its creation was motivated by the need for improved network efficiency and a consistent user experience. By allowing operators to define a maximum call setup duration, networks can more quickly free up resources from failed attempts, improving overall capacity and stability. From a user perspective, it ensures that a failed call attempt concludes in a predictable timeframe, allowing the user to retry or attempt other actions. The timer's implementation within the secure USIM also means its operation is trusted and consistent across different mobile devices, as it is governed by the operator-provisioned SIM card rather than variable device software.
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (29 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-6, normative work from Rel-15.
In Release 15, updates were made to USIM management procedures for 5GS, including enhancements to the USIM OPL configuration to support a 3-byte TAC when in NG-RAN. The release also introduced a USIM Service Table update for PDU session call control support and allowed for the configuration of Mission Critical Services data via the USIM.
- USIM Service Table update for PDU session call control support TS 31.102CR0786
- Allow configuration of MCS (Access Identity 2) via USIM. TS 31.102CR0794
- Mission Critical Services configuration data update to USIM TS 31.102CR0808
- Update EFHPPLMN description to clarify timer T interpretation based on the RAT in use. TS 31.102CR0795
- Enhance USIM OPL configuration to support 3 bytes TAC when in NG-RAN. TS 31.102CR0818
- Updates to USIM management procedures for 5GS TS 31.102CR0806
+ 1 more changes
In Release 16, the new functionality for the Outgoing Call Timer (OCT) was not explicitly detailed in the provided Change Requests or grounding context. The listed CRs focus on enhancements for USIM configuration and storage, such as for the RLOS PLMN list, URSP, and PS Data Off lists, but do not contain specific technical details about changes to the OCT function itself. Therefore, based solely on the given materials, no new OCT features for Release 16 can be described.
- Support for USIM configuration of RLOS PLMN list TS 31.102CR0847
- URSP storage in USIM TS 31.102CR0861
- Specify storage for a potentially separate KSEAF for non-3gpp access on the USIM TS 31.102CR0864
- USIM configuration of RLOS allowed MCC list TS 31.102CR0881
- Support for Trusted non-3GPP access networks list by USIM TS 31.102CR0891
- Dedicated AID for USIM Applications with non-IMSI based SUPI Types TS 31.102CR0897
+ 3 more changes
In Release 17, the primary new feature for the Outgoing Call Timer (OCT) function was the introduction of a multiplier coefficient to adjust the high priority PLMN search timer. This enhancement allows for more flexible configuration of the timer's duration based on network or subscriber-specific requirements. The adjustment mechanism is managed through parameters stored on the USIM.
- Introduce a USIM file to store pre-configured CAG information list TS 31.102CR0904
- SOR-CMCI storage in USIM TS 31.102CR0917
- Addition of USIM files for the indication of whether disaster roaming is enabled in the UE, disaster roaming wait range, disaster return wait range and applicability indicator for disaster roaming PLMNs list provided by VPLMN. TS 31.102CR0938
- Adding eDRX parameters in the USIM for NG-RAN TS 31.102CR0943
- 5G NSWO (Non-Seamless WLAN Offload) configuration support in the USIM compromised proposal. TS 31.102CR0946
- Support of 'No E-UTRA Disabling In 5GS' in USIM TS 31.102CR0947
+ 3 more changes
In Release 18, the OCT function was not updated; the provided Change Requests and grounding context do not describe any changes to the Outgoing Call Timer. The specified enhancements for Release 18 instead focus on USIM applications, including extending security parameter storage, adding an Access Control EF for GBA_U_APIs, and adding an EF for IMS Data Channel configuration.
In Release 19, the specification introduced new backward compatibility handling for the USIM when it lacks extended security parameter storage in the EF_5GAuthKeys file. This ensures that network access and security procedures can function correctly even with USIMs that do not support this specific storage capability. The update focuses on maintaining operational continuity for user equipment during authentication processes.
- Backward compatibility handling of USIM without extended security parameter storage in EF_5GAuthKeys - Rel19 TS 31.102CR1074
Explore further
Broader topics and technologies where OCT plays a role.
Defining Specifications
3GPP specifications that define or reference OCT, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TR 21.905 vj00 | 3GPP Technical Terms and Definitions | Rel-19 |
| TS 31.102 vj40 | USIM Application Specification | Rel-19 |