A quick RU to DU to CU to Core of 5G vRAN

This post is a brief collection of some basic understandings that I have gathered around 5G virtualized Radio Access Network (vRAN) operations, and a little about where Dell Technologies plays a part.

Example of Cell Tower (pic by @PedroClarke1)

Probably the most recognisable telecommunications sight, for me, is that of a radio or cell tower with the various antennae pointing off in different directions. Upon closer inspection, there’s generally a lot of hardware up there, with large cables running to the base unit.

Upon joining the Dell Telco Systems Business, I started to learn about the various telecom components and associated acronyms, one of which is an RRU (Remote Radio Unit). It turns out that these RRUs are the white boxes that I have seen on various masts, just below the antennae themselves.

Among other functions, the RRU takes signals from the antenna, converting RF signal into Data signal, and vice versa as required, before sending that signal to the baseband unit (BBU) at ground level (via CPRI over fiber cable). This is referred to as the ‘Fronthaul’.

RAN architectures are changing with 5G, with the disaggregation of network services. Whereas previously the RRU to BBU connection would be a single, proprietary connection, now with Network Function Virtualization (NFV), the services previously provided by the RRU and BBU/gNB can be split out into Radio Units (RUs) Distributed Units (DUs) and Centralised Units (CUs). This functional ‘split’ is subject to 3GPP standards, more here.

What’s the benefit of splitting these functions?

A split architecture allows for more flexibility, enabling engineers to optimise performance features such as latency and cost.

The CU and DU functions can run as virtual software functions on standard commercial off-the-shelf (COTS) hardware, and providing the DU and CU infrastructure is where Dell starts to gets involved …

Distributed Units

As before with the RRU to BBU, the connection from the RU to the DU is referred to as the ‘Front Haul’. A Distributed Unit (DU) includes both baseband processing and RF functions. A DU needs to be closer to the RU (<20km), for latency requirements (micro seconds), and physically requires units of a small/compact profile that can tolerate rugged conditions and extreme temperatures. For DU infrastructure, Dell may position a server such as the XR11 (where the X stands for Extreme Conditions, and R stands for Rugged!).

As can be seen from the image above, capacity is at a premium in these DU cabinets, and can quite often be exposed to the elements, so the servers need to withstand extreme temperatures of -5C to +55C. (Fair to say that this 5G mast and DU location, in Cork City, Ireland will not be seeing +55C any time soon. This link shows the Eir 5G coverage in our area!)

Centralised Units

The CU (Centralised Unit) may be used for bridging the gap/distance back to the core for multiple DUs. Inserting this CU function then means we have a midhaul in addition to the backhaul. The midhaul connection from the DU to the CU has greater range (<80km) as well as more relaxed latency requirements (~ low milliseconds).

For CU infrastructure, Dell may position servers such as XR12, R650 or 750. The XR12 is 2U in height, but is similar to the XR11 wrt depth, ruggedness and certification.

The Backhaul, which always provides the link to the Core, regardless of functional splits, is then shifted to the CU-to-Core connection. The general backhaul connection should be <200km and has latency requirements of ~ tens of milliseconds.

This particular split function architecture is just one example of how a provider may choose to architect their 5G network. More on DU and CU architecture options here.

5G Core

Back in the Core datacenter, hosting the 5G mobile core services and OSS/BSS functions, Dell provides a wide range of hardware and software solutions and services in conjunction with various Partners. The infrastructure requirements in the core datacenter are not subject to the same environmental and capacity challenges as the DU and CU roadside cabinets, therefore the choice of server/storage/networking hardware and platform is much broader.

Dell partners with a range of vendors to provide a choice of cloud-native solutions across partners such as VMware, Red Hat, Nokia, Mavenir, Wind River, and Affirmed. A recent partnership with Nokia and VMware is highlighted here.

More information can be found at the Dell technologies InfoHub for Telco Solutions here.

Automation, Orchestration, Deployment, Lifecycle Management and so much more …

The proliferation of servers now supporting the 5G network reaches far from the Core Datacenter, but FEAR NOT, the rapid deployment and lifecycle management of every node can be tracked, viewed and managed by the recently announced Dell Bare Metal Orchestrator.

I will hopefully be in a position to post more about this BMO product another day, but it’s not the primary focus of this post, so for now, more information can be found in the Solution Brief.

Dell Bare Metal Orchestrator – Map view of infrastructure site locations

Higher up the stack, VMware Telco Cloud Automation is one option that provides CSPs with the ability to easily create, deploy, and manage 5G services through service automation/orchestration, network slicing, and more while deploying resources at the core and the edge of the network as needed (Core, Edge, CU/DU, Far Edge).

The Dell Technologies VMware Telco Cloud Platform Reference Architecture provides more detail on this proven cloud-native platform. I also plan to post some more about this over time.


In this post I have referred to vRAN, but there are other flavours of RAN, and these are perfectly explained in this post: C-RAN vs Cloud RAN vs vRAN vs O-RAN- A simple Guide!

That’s it for now, more to come, thanks for reading, hope that helps!

Steve

Other Resources:

Link to Dell Bare Metal Orchestrator

Link to VMware Telco Cloud Automation

Link to VMware Telco Cloud Platform

Link to VMware Telco Cloud Infrastructure

Open RAN Functional Splits Explained

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