About O-RAN O-CU Testing
Open RAN (O-RAN) architecture disaggregates and splits traditional RAN into CU (Centralized Unit), DU (Distributed Unit), and RU (Radio Unit), supporting standardized open and interoperable interfaces, and allowing key functions to run as virtualized software functions on vendor-neutral hardware. This avoids single-vendor dependency by opening the architecture to multiple suppliers.
The CU sits between the DUs and the core network. The CU handles the higher layers of the protocol stack, where the critical packet processing functions typically reside (SDAP, RRC, and PDCP). A single CU handles many DUs. CUs are also virtualized and can be deployed on inexpensive,vendor-neutral COTS hardware. Cloud deployments are also an option, which brings its own set of challenges.
Disaggregated architecture, open interfaces, virtualization,multi-vendor interworking, and cloud deployments are some of the many challenges that mandate comprehensive testingof the CU.
The CU can be tested in isolation, in wraparound testing mode. In this case, the O-CU test solution emulates all the network functions surrounding the CU, including DUs & UEs, core network, eNBs/gNBs, neighboring CUs, and the RIC. The core network emulation can be 5GC for SA mode or it could be the EPC for NSA mode. The CU can also be tested in an end-to-end configuration, in which case the core network is part of the System Under Test (SUT).
Key Features
The O-CU Testing feature set includes the following capabilities:
• Non-standalone (NSA) and Standalone (SA) modes
• Emulation of UEs, DUs and 5GC and/or EPC to completely surround the CU being tested
• Relevant interfaces F1-C, F1-U, N1, N2, N3, S1-U, S1-MME, X2, Xn are supported
• Control plane and user plane testing
• Functional, performance & capacity testing
• Support for intra-CU & inter-CU mobility scenarios
• High performance solution that can be scaled to 1000s of emulated
DUs, millions of emulated subscribers, 100s of gbps of user plane traffic
• Call modeling capabilities to shape test traffic as needed, for control and user planes
• Highly customizable, with ability to edit messages onsite as needed
• Appliance-based or virtualized deployment options, including ability to deploy on public cloud platforms
• Automation through RESTful or Tcl API
Benefits
The Spirent O-CU solution provides flexibility, scalability, and high-performance for comprehensively testing the CU for compliance, functionality, performance, & capacity. With the need to interoperate with network functions from different vendors, compliance to the specification is of paramount importance. Often, the same specification gets interpreted differently by different vendors. This can manifest itself in whether certain optional Information Elements (IE) are included or not in certain procedures. Message editing capabilities empower users to quickly deal with these situations themselves. Powerful traffic modeling capabilities allow users to shape test traffic as needed, both for the control and user planes. This enables easy replication of live network traffic conditions, patterns, and scale in the lab.
Some of the key use cases that can be addressed include:
• DU, EPC, 5GC, eNBs and gNB interoperability
• CU subscriber capacity
• CU DU capacity
• CU Performance (e.g., registration rate)
• Single UE and aggregate data throughput capacity
• Real-world user plane traffic performance (such as HTTPS, QUIC and application traffic such as Facebook, YouTube, Zoom, etc.)
• Voice and video quality
• Ability to handle real world mix and scale of events, including different types of mobility events
• CU robustness for handling abnormal, non-compliant messages & scenarios
• CI/CD automation pipeline integration
Test Cases
An intuitive, easy-to-use graphical interface enables quick configuration & execution of tests and analysis of test results. Landslide also provides robust automation options including RESTful & Tcl APIs. - Using the RESTFul API , Using the TCL API
gNB CU NSA Nodal test case - Adds gNB CU testing to a Landslide C100 test system.
Includes F1-C, F1-U, X2-C, X2-U RAN interfaces.
- gNB CU NSA Nodal Test Configuration , gNB CU NSA Nodal Parameters , About gNB CU NSA F1-U Interface Testing
gNB CU SA Nodal test case - Includes F1-C, F1-U, Xn-C, Xn-U RAN interfaces.
- gNB CU SA Nodal Test Configuration , gNB CU SA Nodal Parameters , About gNB CU SA F1-U Interface Testing
gNB CU Node test case - Includes F1-C, F1-U, Xn-C, Xn-U RAN interfaces.
Technical Specifications
Landslide O-CU Testing is compliant to to Release 15 of the following 3GPP specifications:
• 3GPP TS 24.301 Non-Access-Stratum (NAS) protocol for Evolved Packet System (EPS); Stage 3
• 3GPP TS 24.501 Non-Access-Stratum(NAS) protocol for 5G System (5GS); Stage 3
• 3GPP TS 29.281 General Packet Radio System (GPRS) Tunneling Protocol User Plane (GTPv1-U)
• 3GPP TS 36.331 Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC) protocol specification
• 3GPP TS 36.413 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 Application Protocol (S1AP)
• 3GPP TS 36.423 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 application protocol (X2AP)
• 3GPP TS 37.324 E-UTRA and NR; Service Data Adaptation Protocol (SDAP) specification
• 3GPP TS 37.340 NR; Multi-connectivity; Overall description; Stage-2
• 3GPP TS 38.300 NR;NR and NG-RAN Overall Description
• 3GPP TS 38.323 Packet Data Convergence Protocol (PDCP) Specification
• 3GPP TS 38.331 Radio Resource Control (RRC) protocol specification
• 3GPP TS 38.401 NG-RAN; Architecture description
• 3GPP TS 38.413 NG-RAN; NG Application Protocol (NGAP)
• 3GPP TS 38.415 NG-RAN; PDU Session User Plane Protocol
• 3GPP TS 38.423 NG-RAN; Xn Application Protocol (XnAP)
• 3GPP TS 38.425 NG-RAN; NR User Plane Protocol
• 3GPP TS 38.473 NG-RAN; F1 Application Protocol (F1AP)
Definitions:
- ORAN – Open RAN
- O-CU - (Centralized Unit) - O-RAN Central Unit – a logical node hosting PDCP, RRC, SDAP and other control functions. This can be considered short-hand for the O-CU-CP and O-CU-UP in an O-RAN system.
- O-DU – (Distributed Unit) - O-RAN Distributed Unit: a logical node hosting RLC/MAC/High-PHY layers based on a lower layer functional split. O-DU in addition hosts an M-Plane instance.
- O-RU – (Radio Unit) - O-RAN Radio Unit: a logical node hosting Low-PHY layer and RF processing based on a lower layer functional split. This is similar to 3GPP’s “TRP” or “RRH” but more specific in including the Low-PHY layer (FFT/iFFT, PRACH extraction). O-RU in addition hosts M-Plane instance.
- C-Plane - Control Plane: refers specifically to real-time control between O-DU and O-RU, and should not be confused with the UE’s control plane.
- S-Plane - Synchronization Plane: Data flow for synchronization and timing information between nodes
- U-Plane - User Plane: refers to IQ sample data transferred between O-DU and O-RU
- NSA - Non-Stand-Alone network mode that supports operation of SgNB attached to MeNB
- SA - Stand-Alone network mode that supports operation of gNB attached to a 5G Core Network
5G Glossary Acronyms, Terms and Specifications in 5G-Glossary