Description
Overload Control Information (OCI) is a protocol-level mechanism designed to manage and mitigate overload conditions within the IP Multimedia Subsystem (IMS) and the 5G Service-Based Architecture (SBA). It operates by allowing a network function that is experiencing high load (the overloaded entity) to inform its peer functions (the clients) about its current capacity status. This information is typically embedded within protocol responses, such as SIP responses in IMS (e.g., 503 Service Unavailable) or within HTTP/2 messages in the 5G core (e.g., Nudm_UEContextManagement response). The OCI contains parameters that instruct the client on how to adjust its request traffic. Key parameters include a 'retry-after' value, which specifies a duration during which the client should refrain from sending new requests, and potentially more granular controls like a probability factor, where the client is instructed to discard a certain percentage of new requests before sending them. In 5G SBA, OCI is formalized as part of the overload control procedures in TS 29.500. A consumer NF (client) sending a service request to a producer NF (server) includes its own overload control preferences in the request. If the producer is overloaded, it can respond with OCI that includes a 'load control information' element, dictating a reduction factor and a validity period. The consumer NF must then apply this reduction to its request rate towards that producer. The mechanism is dynamic and stateful, allowing load to be managed in real-time. It works in conjunction with other resilience features like load balancing and stateless design to ensure that a single point of overload does not cascade into a wider network failure.
Purpose & Motivation
OCI was created to address the critical problem of signaling overload in all-IP core networks, which became prominent with the deployment of IMS for multimedia services. Traditional telephony switches had hardware-based overload controls, but software-based, IP-connected NFs are susceptible to being overwhelmed by signaling storms—sudden surges in traffic that can be caused by mass call events, network failures, or malicious attacks. Without a standardized overload control mechanism, an overloaded server might crash, drop connections indiscriminately, or become unresponsive, leading to a cascading failure that affects service across the network. OCI provides a graceful and cooperative way to handle such conditions. It allows an overloaded NF to proactively protect itself by instructing its peers to reduce their request load, rather than simply rejecting requests, which can cause clients to retry aggressively and exacerbate the problem. Its introduction in Release 6 for IMS and later refinement for the 5G SBA was motivated by the need for robust, scalable, and self-regulating networks that can maintain service continuity for priority users (e.g., emergency calls) even under extreme load, fulfilling regulatory and reliability requirements.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (41 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, the Overload Control Information (OCI) function was not newly introduced or modified based on the provided CR titles and grounding context. The listed Change Requests focus on USIM/EF updates for 5G security contexts, access identities, and service tables, with no mention of OCI procedures, interfaces, or capabilities. Therefore, the grounding materials indicate no specific technical update to the OCI function in this release.
- Introduce EFs that contain NAS full native security context from 5G Mobility Management Information. TS 31.102CR0776
- Introduce an EF that contains 5G UAC Access Identity Information TS 31.102CR0780
- USIM Service Table update for PDU session call control support TS 31.102CR0786
- Remove the control plane based SoR related EF and use only the EF-UST. TS 31.102CR0798
- Corrections to the control plane based SoR related EF TS 31.102CR0799
In Release 16, the Overload Control Information (OCI) function was enhanced to support the **"Enhanced Coverage Mode"** for control procedures, allowing for improved management of devices in challenging radio conditions. Additionally, new mechanisms were introduced for the **storage of 5GMM information**, specifically to handle counters related to the **SOR counter** and a **UE parameter update counter**, which are essential for managing network-initiated updates and steering of roaming operations. These updates provided more granular control and resilience for network overload scenarios.
In Release 17, the key new development for the Overload Control Information (OCI) function was the introduction of support for load and overload control for northbound APIs. This enhancement specifically extended OCI mechanisms to manage congestion on these API interfaces. No other changes to OCI were specified in the provided materials.
- Supporting Load and Overload Control for northbound APIs TS 29.122CR0492
- Introduce a USIM file to store pre-configured CAG information list TS 31.102CR0904
- Support of QoS notification control for requested alternative QoS parameters TS 29.122CR0580
- Reporting condition for QoS Monitoring Information TS 29.122CR0607
- Introduction of a CAG-ID range in the CAG information list TS 31.102CR0927
- Clarification of CAG-ID range indication in the CAG information list for HPLMN or EHPLMN TS 31.102CR0960
+ 1 more changes
In Release 18, the Overload Control Information (OCI) function was enhanced to support the measurement and reporting of congestion information, providing a new capability for network monitoring. Furthermore, the release generalized the description for QoS monitoring control and removed previously unspecified QoS monitoring control options to streamline the function. These updates built upon the existing foundation of Connection Admission Control (CAC) mechanisms used by the network to balance QoS requirements and utilization.
- Update Flow Description Information with ToSTC in ChargeableParty API TS 29.122CR0634
- Update Flow Description Information with ToSTC in AsSessionWithQoS API TS 29.122CR0636
- Network slice admission control notification update for UE with atleast one PDU session/PDN connection TS 29.122CR0732
- Support of the congestion information measurement and reporting TS 29.122CR0741
- Support the provisioning of periodicity information at service data flow level TS 29.122CR0814
- Support of UL and DL policy control based on Round-Trip latency requirements TS 29.122CR0851
+ 7 more changes
In Release 19, the Overload Control Information (OCI) function was enhanced with new capabilities for reporting rate limitation information and QoS notifications. Specifically, it introduced support for an AF request rate limitation information reporting procedure and an updated mechanism for reporting the QoS notification event with direction information. These additions provided the network with more granular control and monitoring during congestion scenarios.
- Introduce (S)RTP Multiplexed Media Information TS 29.122CR0889
- Support Energy related information exposure TS 29.122CR0898
- Support of on-path N6 signaling information to deliver Media related information TS 29.122CR0902
- Support of AF request rate limitation information reporting TS 29.122CR0903
- Update rate limit information reporting TS 29.122CR0942
- Enhancements on Data Rate Limitation Information for Non-GBR service data flow TS 29.122CR0948
+ 8 more changes
Explore further
Broader topics and technologies where OCI plays a role.
Defining Specifications
3GPP specifications that define or reference OCI, 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 29.122 vj40 | T8 Reference Point for Northbound APIs | Rel-19 |
| TS 29.500 vj50 | 5GC Service Based Architecture Specification | Rel-19 |
| TR 29.843 vg00 | 5GC Load and Overload Control Study | Rel-16 |
| TS 31.102 vj40 | USIM Application Specification | Rel-19 |