Short answer: Huawei RRUs such as the RRU3971 and RRU5904 connect to a BBU3900, BBU3910 or BBU5900 through CPRI fiber links that terminate on the baseband side, typically on a UBBP board. Whether a given RRU will work with a given BBU is rarely a question of the chassis itself. It depends on four things: the CPRI port rate both ends support, the optical modules in between, the baseband board installed, and whether the base station software release includes the RRU’s software components. This guide walks through each point so you can plan a used RRU deployment without surprises.
How a Huawei RRU connects to the BBU
In Huawei’s distributed base station architecture, the BBU handles baseband processing and the RRU handles RF: it modulates and demodulates baseband and RF signals, amplifies power and detects standing waves. The two are joined by a CPRI (Common Public Radio Interface) link carried over optical fiber.
On the BBU side, Huawei documentation describes the UBBP universal baseband processing unit as providing six CPRI ports, labelled CPRI0 to CPRI5, using SFP connectors. These are the data ports that connect the BBU to its RF modules. The UBBP also carries an HEI port (QSFP) used for interconnection with other baseband boards. UBBP boards can be configured in a BBU3900 or BBU3910, and the BBU5900 supports UBBP boards as well, including the UBBPe4, UBBPg1a and UBBPg2 listed on Huawei’s DBS5900 product page.
For the BBU chassis itself, see our Huawei BBU5900 and Huawei BBU3910 product pages. Board-level slot and board compatibility inside the chassis is covered in our earlier article on BBU5900 board compatibility (UBBP and UMPT).
CPRI specifications of common Huawei RRUs
The table below summarises the CPRI-related specifications published in Huawei’s RRU3971 description, alongside what to check for the RRU5904. Always confirm against the technical specification document for the exact band variant you are deploying.
| Item | RRU3971 | RRU5904 |
|---|---|---|
| Number of CPRI ports | 2 | Check the RRU5904 Technical Specifications for your band variant |
| CPRI data rates | 1.25, 2.5, 4.9 and 9.8 Gbit/s | Listed per band in the RRU5904 Technical Specifications |
| Topology | Star, chain or dual-star | Listed per band in the technical specifications |
| Cascading levels (CPRI MUX) | GU: 6, GL: 4, UL: 4 | Listed per band and mode |
| Radio modes | GSM, UMTS, LTE; dual-mode or triple-mode by software configuration | Multi-mode; later releases added NR FDD support for the 1800 MHz and 2100 MHz versions |
| TX/RX | 4T4R | 4T4R |
| Power input | -48 V DC (-36 V to -57 V DC) | See technical specifications |
If you are choosing between these two radios, our RRU5904 vs RRU3971 comparison covers the differences in more detail.
Four compatibility checks before connecting a used RRU
1. CPRI port rate on both ends
A CPRI link only comes up at a rate that both the RRU port and the baseband board port support. The RRU3971, for example, supports 1.25, 2.5, 4.9 and 9.8 Gbit/s. Different UBBP generations support different maximum CPRI rates, so the planned cell configuration (bandwidth, number of carriers, MIMO) has to fit within the rate the baseband board can actually deliver. Huawei’s RRU indicator descriptions list mismatched data rates on CPRI ports as one of the causes of a CPRI link out-of-lock alarm, which is a common symptom when this check is skipped.
2. Optical modules
The SFP modules at each end must match the required CPRI rate and the fiber type. Huawei’s documentation notes that some older RRU hardware cannot use optical modules that support a 9.8 Gbit/s CPRI rate, and that Huawei wireless equipment should use optical modules certified by Huawei. When you buy used RRUs, confirm whether optics are included and what rate they are rated for.
3. Baseband board and mode
The RRU’s working mode (GSM, UMTS, LTE, or a multi-mode combination such as GL or UL) must be supported by the baseband board serving it. A UBBP that supports LTE FDD will not serve GSM carriers unless that board variant also supports GSM. For multi-mode sites, check that the installed UBBP supports the specific co-BBP or multi-mode combination you plan to run. Our Huawei UBBPg2 page is a common choice for BBU5900 LTE deployments.
4. Software release
Huawei RRUs require matching hardware and software versions. The RRU3971 description, for example, states that the RRU3971 can be used with SRAN9.0, SRAN10.1 and SRAN11.1, which include its software components. New features also arrive by release: the RRU5904 technical specifications record NR FDD support being added to the 1800 MHz and 2100 MHz versions in a later software version. Before deployment, confirm that the base station software on site lists the RRU model and the features you need in Huawei’s software and hardware compatibility description.
Topology and cascading
Huawei RRUs typically support star, chain and dual-star topologies. In a star topology, each RRU has its own CPRI link back to the BBU. In a chain, RRUs are cascaded and share the CPRI link, which saves fiber and BBU ports but limits capacity and adds dependency between units. For the RRU3971, Huawei lists CPRI MUX cascading limits of six levels for GU and four levels for GL and UL. Plan cascades conservatively when mixing older and newer radios, and check the cascading limit for the mode you actually run.
Practical checklist for used RRU and BBU combinations
- Record the RRU model, band and BOM code from the label, and match it against the band you have licensed.
- Confirm the baseband board model in the BBU (UBBPd, UBBPe or UBBPg family) and its supported modes and CPRI rates.
- Use optical modules rated for the planned CPRI rate on both ends.
- Check that the site software release includes the RRU model and required features.
- After installation, verify the CPRI link indicators and clear any CPRI alarms before commissioning cells.
- Run a VSWR check on each RF port before putting the unit into service.
Popular radios for these combinations include the Huawei RRU3971 1800 MHz and the Huawei RRU5904 1800 MHz. The full range is on our Huawei category page.
FAQ
Can an RRU3971 work with a BBU5900?
The RRU connects to the baseband board, not directly to the chassis, so the question is whether the UBBP installed in the BBU5900 supports the RRU’s mode and CPRI rate, and whether the site software release supports the RRU3971. Check the software and hardware compatibility description for your release before deployment.
Why does a CPRI link stay down after connecting a used RRU?
Common causes include mismatched CPRI rates between the RRU and the baseband board, unsuitable or uncertified optical modules, a damaged fiber, or an RRU model that the installed software release does not support.
How many CPRI ports does a UBBP board have?
Huawei documentation describes six CPRI ports on the UBBP, labelled CPRI0 to CPRI5, using SFP connectors.
Can RRUs be cascaded on one CPRI link?
Yes, Huawei RRUs such as the RRU3971 support chain topology. The number of cascading levels depends on the mode; for the RRU3971, Huawei lists six levels for GU and four for GL and UL.
Buy tested Huawei RRUs and BBUs
Every unit we sell is functionally tested before shipment, and radio units such as RRUs are also VSWR tested. All equipment comes with a 90-day warranty, and we ship worldwide in secure packaging. Contact us on WhatsApp at +86 187 3329 4669 or +86 139 3088 8705, email jack@telecombts.com, or use the form at https://telecombts.com/contact-us/. We also buy surplus Huawei, Ericsson and Nokia equipment: see sell your equipment.