Description
The Processing Cross-check Organization (PCO) is a conceptual and architectural framework defined within 3GPP specifications to ensure the integrity and correctness of processing functions, with a primary application in Lawful Interception (LI) systems. It operates by establishing mechanisms to verify that the processing of intercepted communication content and associated interception-related information (IRI) is performed accurately and without corruption or unauthorized modification. This involves cross-checking the output of processing functions against expected results or through redundant processing paths to detect errors or inconsistencies.
Architecturally, the PCO framework interfaces with key LI functional entities such as the Intercepting Control Element (ICE), which performs the actual interception within the network, and the Delivery Functions (DF2 and DF3), which handle the transport of intercepted data to the Law Enforcement Monitoring Facility (LEMF). The PCO may employ techniques like checksums, sequence numbers, cryptographic integrity protection, or comparison with duplicate processing streams to validate that data has been processed correctly from the point of interception through to delivery.
Its role in the network is primarily one of assurance and compliance. By providing a verifiable trail and validation of processing steps, the PCO helps network operators and authorities demonstrate that intercepted data is a true and accurate representation of the target's communications, which is a fundamental legal requirement for lawful interception. It addresses risks related to software bugs, hardware faults, or malicious tampering within the interception infrastructure.
Purpose & Motivation
The PCO was introduced to address the critical need for verifiable accuracy and reliability in lawful interception systems. As telecommunications networks became more complex and digital, ensuring that intercepted data remained intact and unaltered during processing became a significant technical and legal challenge. Legal frameworks worldwide mandate that intercepted evidence must be authentic and reliable to be admissible in court, necessitating technical mechanisms to prove the integrity of the interception process.
Prior to formalized concepts like PCO, reliance was placed on less systematic methods of ensuring processing integrity, which could be insufficient for rigorous legal scrutiny. The creation of the PCO framework within 3GPP standards provided a structured, standardized approach to this problem. It defines specific requirements and potential methods for cross-verification, enabling equipment vendors and network operators to implement solutions that meet stringent compliance demands. Its development was motivated by the evolving regulatory landscape and the need for international technical standards to support lawful interception across different jurisdictions and network technologies.
Release Timeline
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (17 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the PCO function was enhanced to enable network-initiated restoration of IMS services following a P-CSCF failure. Specifically, it introduced a procedure where the PDN-GW, upon detecting a failure, sends a new list of available P-CSCF addresses within a PCO IE to update all affected UEs. Furthermore, it defined a new UE capability indication (P-CSCF Re-selection support) within the PCO to allow the network to employ this restoration mechanism.
- Corrections for MTU PCO parameters handling TS 24.501CR0374
In Release 16, enhancements to the PCO function included the standardized usage of the ACS information as a PCO parameter and improved handling for encapsulating multiple QoS rule or flow parameters within a single PCO/ePCO container. Furthermore, the release formalized procedures for P-CSCF restoration, introducing a specific PCO parameter (0012H) for UE capability indication and enabling the network to provide updated P-CSCF address lists or a failure indicator via PCO during bearer modification.
In Release 17, the enhancements for the PCO function included clarifying the usage of 5GS parameters within the (e)PCO or APCO and defining procedures for handling PCO parameters during inter-system changes, such as allowing the UE to use the PCO IE after a change from N1 to S1 mode. The release also introduced specific error checks for unstructured PDU session types within PCO and established rules for deleting PCO parameters after a handover between 3GPP and non-3GPP access systems.
- EDC related PCO parameters usage TS 24.501CR3848
- PVS PCO parameter providing TS 24.501CR3382
- Correction of PCO related terminology TS 24.501CR3434
- Delete the PCO parameters after handover between 3GPP and non-3GPP access TS 24.501CR3737
- UE is allowed to use PCO IE after inter-system change from N1 mode to S1 mode TS 24.501CR4027
- QoS error checks for unstructured PDU session type in PCO TS 24.501CR4322
+ 2 more changes
In Release 18, the PCO function was enhanced with new UE and network capabilities for P-CSCF restoration, including a specific UE support indicator for this extension over WLAN access. The release also introduced procedural cleanup, such as refining parameter naming and defining UE handling for syntactical errors in PCO during QoS operations. Furthermore, it specified mechanisms for the network to provide a new P-CSCF address list or a P-CSCF failure indicator within the PCO to UEs when a failure is detected.
- Resolving the EN related to the inclusion of SDNAEPC support indicator in the PCO or the ePCO TS 24.301CR3871
- Remove description on inclusion of ATSSS response in (e)PCO TS 24.301CR3890
- Cleanup of PCO parameters naming TS 24.301CR3889
- QoS error checks for unstructured PDU session type in PCO TS 24.501CR4462
- UE handling on PCO or EPCO syntactical errors in QoS operations TS 24.501CR4879
In Release 19, the enhancements for the PCO function introduced a specific P-CSCF failure indicator within the PCO information element to explicitly notify UEs of a failure, alongside the existing mechanism to provide a new list of available P-CSCF addresses. The release also defined the UE's capability to indicate support for P-CSCF re-selection and restoration extensions during PDN connection establishment, particularly for WLAN access via the TWAN. Furthermore, the procedures were detailed for the PDN-GW to initiate bearer modification using PMIP Update Notification messages to propagate these PCO updates through the network.
- Correction to ATSSS request PCO parameter TS 24.193CR0233
Explore further
Broader topics and technologies where PCO plays a role.
Defining Specifications
3GPP specifications that define or reference PCO, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.380 vj10 | IMS Restoration Procedures | Rel-19 |
| TR 23.979 vj00 | PoC over 3GPP Systems Architectural Requirements | Rel-19 |
| TR 23.981 vj00 | IPv4 IMS Interworking and Migration Study | Rel-19 |
| TS 24.193 vj50 | ATSSS Procedures Specification | Rel-19 |
| TS 24.229 vj50 | IMS call control protocol based on SIP and SDP | Rel-19 |
| TS 24.244 vj00 | Wireless LAN Control Plane Protocol | Rel-19 |
| TS 24.301 vj60 | NAS protocol for Evolved Packet System | Rel-19 |
| TS 24.302 vj00 | Access to EPC via non-3GPP networks; Stage 3 | Rel-19 |
| TS 24.501 vj50 | 5G NAS Protocols Specification | Rel-19 |
| TR 26.996 vj00 | ISAR Split Rendering Audio Characterization | Rel-19 |
| TS 29.061 vj00 | Packet Domain Interworking for PLMN | Rel-19 |
| TS 29.274 vj50 | GTPv2-C Control Plane Protocol Specification | Rel-19 |
| TS 29.806 vc10 | P-CSCF Restoration Analysis & Solutions | Rel-12 |
| TS 29.826 vd10 | P-CSCF Restoration Enhancements for WLAN | Rel-13 |
| TR 33.739 vi10 | Study on security enhancement of support for | Rel-18 |
| TS 36.305 vj00 | UE Positioning in E-UTRAN Stage 2 | Rel-19 |
| TS 38.305 vj00 | NG-RAN UE Positioning Stage 2 | Rel-19 |
| TR 38.859 vi10 | Technical Report | Rel-18 |
