Description
Steering of Roaming Connected Mode Control Information (SOR-CMCI) is a control mechanism introduced in 3GPP Release 17 that works in conjunction with Steering of Roaming (SOR) data. It is a parameter delivered by the network to a User Equipment (UE) that is in CONNECTED mode (e.g., RRC_CONNECTED in NG-RAN), providing instructions on when the UE should process and apply newly received SOR information. The SOR-CMCI is included within the SOR transparent container that is sent from the Access and Mobility Management Function (AMF) to the UE via a DOWNLINK NAS TRANSPORT message.
The SOR transparent container, defined in 3GPP TS 24.501, carries the SOR data itself and the associated SOR-CMCI. The SOR-CMCI parameter is a 3-bit field that conveys specific commands to the UE. The primary commands are: 'apply immediately' and 'apply when in idle mode'. When the UE receives SOR information with an 'apply immediately' indication, it must initiate the steering of roaming procedure straight away, even though it is in connected mode. This typically involves the UE leaving connected mode, evaluating the preferred PLMN list from the SOR data, and potentially selecting a new cell/PLMN, which may trigger a registration procedure on a new network.
If the SOR-CMCI indicates 'apply when in idle mode', the UE stores the SOR information and defers its application until the next time it transitions to idle mode (e.g., after the RRC connection is released). This mechanism gives the network precise control over the timing of the steering action. The inclusion of SOR-CMCI addresses a key scenario: without it, a UE in connected mode receiving SOR data might not apply it until an unspecified later time, potentially delaying critical network steering decisions. The secure packet within the SOR data, which is integrity protected and encrypted for the UE, also includes a hash of the SOR-CMCI to ensure its authenticity and prevent tampering.
Purpose & Motivation
SOR-CMCI was introduced to solve the timing ambiguity problem associated with delivering Steering of Roaming information to a UE that is actively in a connected session. In the initial Release 16 SOR procedures, when SOR data was sent to a UE in connected mode, the standard did not explicitly mandate when the UE should execute the steering procedure. This could lead to unpredictable behavior and delays, undermining the operator's ability to dynamically manage roaming traffic in near-real-time. For effective traffic steering, especially in response to changing network conditions or commercial triggers, the home operator needs certainty about when the steering policy will be enacted.
The creation of SOR-CMCI provides the network with explicit control, allowing it to command an immediate steering action (which may interrupt an ongoing session) or to schedule it for a more convenient time (at the next idle period). This enables more sophisticated and reliable roaming management strategies. For instance, an operator might use 'apply immediately' for urgent steering away from a congested partner network, while using 'apply when in idle mode' for less time-critical policy updates, improving both network efficiency and the subscriber experience by avoiding unnecessary session drops where possible.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (542 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the SOR-CMCI function was newly introduced to support 5GS new steering of roaming procedures. Specifically, the control plane based SoR related EF was removed, mandating the use of only the EF-UST for this functionality. This change streamlined the mechanism for delivering steering of roaming information to a UE in connected mode.
- Establishment of N1 NAS signalling connection due to change in the network slicing information TS 24.501CR0169
- 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
- 3GPP PS Data Off - update to services for roaming TS 31.102CR0784
- Support of 5GS new steering of roaming procedures TS 31.102CR0785
- USIM Service Table update for PDU session call control support TS 31.102CR0786
+ 47 more changes
In Release 16, the SOR-CMCI function was enhanced to support new connected mode control mechanisms for steering of roaming, including service gap control for enforcement in both the UE and AMF. This release also introduced specific activation procedures and the ability to provide new time values via the UE Configuration Update (UCU) procedure. Furthermore, support was added for small data rate control and serving PLMN rate control, expanding the network's ability to manage UE behavior while roaming.
- SINE_5G: Back-off control and retry restriction mechanisms in 5GS TS 24.501CR0730
- Usage of ACS information PCO parameter TS 24.501CR0938
- Small data rate control, general description TS 24.501CR0970
- Small data rate control, activation TS 24.501CR0971
- Serving PLMN rate control, general description TS 24.501CR0972
- Serving PLMN rate control, activation TS 24.501CR0973
+ 123 more changes
In Release 17, the SOR-CMCI (Steering of Roaming Connected Mode Control Information) function was enhanced with new transport and usage procedures, allowing this information to be delivered to a UE in 5GMM-CONNECTED mode. Furthermore, a specific SOR security check criterion was added to the SOR-CMCI to ensure its integrity and authenticity. These alignments and clarifications provided a more robust mechanism for steering roaming decisions while the UE has an active NAS signalling connection.
- Usage of initial CAG information list TS 24.501CR2774
- PVS information providing in PDU session establishment for onboarding TS 24.501CR3323
- Introducion of Network Slice Admission Control TS 24.501CR3111
- Clarificaiton on behaviors of the UE and the network supporting Network Slice Admission Control TS 24.501CR3112
- SOR-CMCI transport and usage TS 24.501CR3207
- Deregister for disaster inbound roaming services TS 24.501CR3512
+ 118 more changes
In Release 18, the SOR-CMCI function was enhanced to operate in 5GMM-CONNECTED mode with RRC inactive indication, allowing for steering of roaming control while the UE remains in a connected state. The release also introduced the capability for network slice usage control and the delivery of S-NSSAI location availability information during the registration procedure. Furthermore, support was added for providing equivalent SNPN information to lower layers to influence cell reselection.
- Equivalent SNPNs usage for NSAG information storage TS 24.501CR4837
- Equivalent SNPNs usage for congestion control TS 24.501CR4838
- Equivalent SNPNs usage in 5GMM-CONNECTED mode with RRC inactive indication TS 24.501CR4839
- Introducing the TNAN information IE TS 24.501CR5123
- Enhanced CAG selection - providing additional information TS 24.501CR4976
- Redundant steering mode is not applicable for ATSSS-LL functionality (impact on TS 24.501) TS 24.501CR5138
+ 145 more changes
In Release 19, the SOR-CMCI function was enhanced with new capabilities for RAT utilization control, including its support during periodic registration updates and its storage in non-volatile memory. The release also introduced handling for RAT utilization restriction information and extended the control to apply to equivalent PLMNs. Furthermore, procedures were updated to ensure the RAT utilization control information is managed within the UE parameters update container and applied when the UE is in a 5GMM-CONNECTED mode.
- The clarification of the applicability of RAT utilization control TS 24.501CR6350
- Control of UE RAT utilization by 5GS TS 24.501CR6343
- The handling on the RAT utilization restriction information TS 24.501CR6377
- Storage and replacement of RAT utilization control information associated to the current PLMN TS 24.501CR6460
- RAT utilization control support in 3GPP access TS 24.501CR6461
- Storing RAT utilization control information in non-volatile-memory TS 24.501CR6468
+ 79 more changes
Explore further
Broader topics and technologies where SOR-CMCI plays a role.
Defining Specifications
3GPP specifications that define or reference SOR-CMCI, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 24.501 vj50 | 5G NAS Protocols Specification | Rel-19 |
| TS 31.102 vj40 | USIM Application Specification | Rel-19 |
| TS 31.111 vj30 | USIM Application Toolkit (USAT) Specification | Rel-19 |