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C-RAN vs Cloud RAN vs vRAN vs O-RAN- A simple Guide!

OK, you have heard enough of these terms perhaps from RAN vendors? C-RAN vs Cloud RAN vs vRAN vs O-RAN in the context of Radio Access Network ( RAN)

However, these terms are not clear to you because everyone out there explains them in a way that is enough to confuse many. The fact is that they are confusing as the terms are similar and there is not a lot of difference in them.

That is where this blog can help to explain these technologies related to RAN architecture. It will settle the explanation of these terms, once for all.

And don’t worry, if you don’t know what is RRU, BBU, CU, DU, fronthaul, mid haul; I will explain all these terms as we go through.

Radio Access Network has evolved quite a bit, so it’s important for you to be aware of all these new terms.

Understanding all this will help in understanding a vendor RAN solution.

C-RAN vs cloud RAN vs vRAN vs O-RAN? Is it that difficult to understand?

Not exactly, once you understand D-RAN, it is easy to understand the rest of them regarding RAN architecture.

Lets go step by step to understand D-RAN first and then moving to other types

The following diagram summarizes the differences but we will explain it in a moment.

D-RAN vs C-RAN vs vRAN vs O-RAN

What is D-RAN?

D-RAN stands for “Distributed RAN”

The diagram below shows distributed RAN. The RRU and BBU are co-located at every cell site. Each cell site with all its radio functions are distributed and connected back to the core network through backhaul.

WHAT IS D-RAN ( Distributed RAN)
What is D-RAN ( Distributed RAN)

What is it ?
BBU: Baseband unit. Manages the whole base station, including operating/maintenance and signaling processing. It decides the “CAPACITY” of the system.
RRU: Remote Radio unit interfaces with an antenna on one end and BBU on the other. It connects to BBU through CPRI interface and converts RF signal into data signal and vice versa. Further, it does filtering and amplification of RF signal. In fact, it decides the “COVERAGE” of the system” 
Antenna: It interfaces a cell phone wirelessly and transmits/receives RF signal. It decides the “SHAPE” of the coverage.
Reference: ITU-T

What is C-RAN / Cloud RAN

C-RAN (Also CRAN) stands for Centralized RAN or Cloud RAN. In fact, I have seen the industry uses these terms interchangeably.

In C-RAN (Cloud RAN) the BBU moves to a centralized location and the cell site only has the antenna and the RRU. This centralization of BBU functionality (also called BBU pool) results in the name centralized RAN or C-RAN.

What is C-RAN ( Centralized RAN/ Cloud RAN)
What is C-RAN ( Centralized RAN/ Cloud RAN) ( Option 1)

This results in a new interface called fronthaul, which is between the RRU and BBU pool. The benefits of C-RAN includes CAPEX and OPEX reduction as deployment and maintenance cost per cell site are reduced because of BBUs centralization. In addition, it improves spectral efficiency and reduces inter channel interferences, as centralized BBUs can share the resources dynamically among the multiple RRUs. The inter-channel interference is eased because of the joint scheduling and processing.

In addition, a second option of the centralized RAN architecture has a further split in BBUs into DU and CU. Here, CU is further towards the core network resulting in a new interface called midhaul.

Option 2: C-RAN with BBU Split
Option 2: C-RAN with BBU Split

What is it ?
Fronthaul
Fronthaul is the link between RRU and BBU (or RRU and DU). It has a strict latency requirements of 100 to 250 µs (one way)
Midhaul: Midhaul is the link between DU and CU.. Midhaul has relaxed latency requirements, which means we can place CU further closer to the core node.
DU: Distributed runs the RLC, MAC, and parts of the PHY layer. We normally place DU closer to RRU.
CU: Centralized Unit handles the RRC and PDCP layers (and SDAP in case of 5G) . One CU can connect to multiple DUs, CU can be co-located with DU or far from DU.

What is vRAN or Virtual RAN?

vRAN decouples the software from Hardware by virtualizing Network Functions. It uses virtualization technologies such as NFV or containers to deploy CU and DU over x86 server. (or virtual BBU on a server). This is like running Functions in software.

So there is no difference between vRAN and C-RAN except that traditionally C-RAN uses proprietary hardware while vRAN uses Network Functions on the server platform. vRAN is infact a type of C-RAN.

What is Virtual RAN ?
What is Virtual RAN ?

Because of vRAN HW/SW decoupling flexibility, we can achieve scalability. This can cause a decrease in hardware costs and application agility as application can be upgraded easily or swapped altogether (which is not easier with traditional hardware).

However, vRAN puts servers to new limits because of the performance expectation. There has been quite an innovation on enhancing server platform to meet the performance needs of vRAN.

What is O-RAN or Open RAN?

Open RAN/O-RAN (from O-RAN alliance) takes vRAN to the next level. While traditionally vRAN is a closed network, as RU, DU and CU, which are all part of the RAN must be bought from the same vendor.

The O-RAN alliance is working on specifications to open the interface between RRU and DU and further between DU and CU. This means that a customer can mix and match the components from different vendors without being locked to one vendor for all these three components, thus resulting in an open RAN network.

WHAT IS OPEN RAN ( O-RAN)
WHAT IS OPEN RAN ( O-RAN)

These new open components as per O-RAN alliance’s specs are called O-RU, O-DU and O-CU (where O stands for Open) which is actually a modular base station software stack on off-the-shelf server hardware.

So that’s it about the different between C-RAN , V-RAN and O-RAN. Hopefully, with this you will easily understand a vendor’s solution and also give you an insight on how Radio Access Networks have evolved over the time. Let me know in the comments if the concept is clear to you?

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Anand Hotchandani
Anand Hotchandani
3 months ago

Very well articulated.

Govindaraj Muthukrishnan
Govindaraj Muthukrishnan
3 months ago

Very Nice

Anuradha Udunuwara
3 months ago

Great piece of work Faisal. When it comes to open RAN, both O-RAN Alliance and TIP OpenRAN are involved. Please include ONFs SD-RAN too, so that this becomes a single source of reference for D/C/V/SD RAN.

Tarun Kapoor
Tarun Kapoor
3 months ago

Described in layman language. Thanks for this really helpful

Anzar A Hasan
Anzar A Hasan
3 months ago

Great presentation.

Nagatheja
Nagatheja
3 months ago

Thank you Faisal. Very helpful.

Aamir
Aamir
3 months ago

These acronyms were indeed confusing , specially for an engineer with no background in RAN/BSS.
Very nicely explained..Thanks Faisal sb

On a side note, what are your views on the technology service providers should use for transmission in front haul links, there is an interesting competition between DWDM and POS, would love to read your take on it.

Thomas Degen
3 months ago

Faisal, as always your new post is a pleasure up to the point with right feeling about what‘s hot by you which is Open–RAN these days. Thank you for your excellent comprehensive summary about the synonyms around O-RAN topic. I‘ve forwarded your article to my esteemed colleagues for internal joy and leisure and external distribution to partners and customers as recommended reference. Looking forward to your next post, have a good weekend, best regards from Cologne/Germany – Thomas

rahul tomer
rahul tomer
3 months ago

very well explained

Marjory Sy
Marjory Sy
3 months ago

thank you for making these concepts easier to understand, especially for someone who has minimum background in wireless networks

Ansar Al-Kayani
Ansar Al-Kayani
3 months ago

complexity Simplified. Thanks Faisal

Ajay
Ajay
3 months ago

Excellent explanation as always!

Kidane Habte
Kidane Habte
2 months ago

Excellent explanation. Thanks to your detailed description. It is really helpful.

Anurag
Anurag
2 months ago

Very well described in short..

Rajesh Ramchandra Bhosale
Rajesh Ramchandra Bhosale
19 days ago

Thanks, Faisal for well-articulated nuggets of aspects of RAN.

Batakrushna Mallik
Batakrushna Mallik
10 days ago

it was very useful for aspirant.

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