# <center><i class="fa fa-edit"></i> Learning the Fundamentals : OpenRAN </center>
###### tags: `Pre-Internship`
:::info
**Goal:**
To gain a basic understanding of the OpenRAN
- [x] What is OpenRan
- [x] How OpenRAN aims to improve previous generations' technology

**Resources:**
[Previous Note](https://www.tutorialspoint.com/lte/index.htm)
[Introduction to OpenRAN video](https://www.youtube.com/watch?v=-fVHO_WCGF8)
[Ferlinda's OpenRAN note](https://hackmd.io/@ferlinda/rJZ5svlWU)
[OSC Training Course](https://hackmd.io/HvThns4FQjS1xScrNdvBmw?view)
:::

## Background
The telecom industry is going through a dramatic change that can be only compared to what data centers experienced in the 2000s – all driven by Moore’s Law. This is driving the need to move from costly, proprietary solutions to COTS and open-based ones, and to create a broader vendor supply chain.

Deploying, maintaining and optimizing networks requires a lot of manual labor and results in high cost. There are traditional, legacy RAN vendors whose solutions are proprietary and siloed for each G. Historically, mobile network operators (MNOs) have been “locked in” to these legacy RAN vendors, which makes maintaining and upgrading networks costly and challenging. However, these challenges can be addressed with the automation/DevOps approach found in Open RAN solutions.

Open RAN (sometimes referred to as ORAN) is a new movement to open up interfaces to reduce cost, driven by the O-RAN Alliance to standardize interfaces and Telecom Infra Project (TIP) to deploy and establish an ecosystem of MNOs and vendors.

In 2G and 3G, the mobile architectures had controllers that were responsible for RAN orchestration and management. With 4G, overall network architecture became flatter and the expectation was that, to enable optimal subscriber experience, base stations would use the X2 interface to communicate with each other to handle resource allocation. This created the proverbial vendor lock-in as different RAN vendors had their own flavor of X2, and it became difficult for an MNO to have more than one RAN vendor in a particular location. The O-RAN Alliance went back to the controller concept to enable best-of-breed Open RAN.

## RAN Evolution
Image Source : Ferlinda's Note
The Image on the left shows how Mobile Towers work in the earlier generations of cellular communications, where BBU and Radio Unit were both put under the tower. But the loss due to attenuation pushed the evolution into the right image, where radio unit is moved into the tower, and called remote radio unit to minimize attenuation.

The image shows that all Radio Access Networks that is being used until now are all propietary, which means every vendor has their own hardware and software for both BBUs and RRUs. Interconnecting different RANs from different Vendors would be a near-impossible chalenge.

A big evolution where BBU is now virtualized (running on a COTS Server + Propietary Software). But keep in mind OpenRAN is not just about virtualization, this approach is still propietary and can't be interconnected with another vendors' RAN.

Has the working principle of Virtualized RAN, but everything is "Open". OpenRAN opens a new chapter in cellular networking wher open interface is introduced. This can be further explained with this example :


## OpenRAN Architecture

**Orchestration/NMS layer with Non Real Time RAN Intelligent Controller**
This block has core algorithm which is owned and deployed by network operators. The algorithms allow modification of RAN behaviors. AI-enabled policies and ML-based models generated messages in RIC non-RT and conveyed to RIC near-RT.

Functions:
1. service and policy management
2. RAN analytics
3. Model-training for the near-RT RAN functionality

**RAN Intelligent Controller (RIC) near-Real Time function layer**
Functions:
1. Provides new functions leveraging embedded intelligence,such as QoS management, connectivity management and seamless handover control.
2. Delivers a robust, secure, and scalable platform that allows for flexible on-boarding of third-party control-applications.
3. Leverages a database called the Radio-Network Information Base (R-NIB) which captures the near real-time state of the underlying network
4. Feeds various RAN measurements data, to the near-RT RIC to facilitate radio resource management
5. Provides initiate configuration commands to CU/DU.
6. Receives an AI model from RIC non-RT and execute it to change the functional behavior of the network

More on CU, RU and DU can be read on [Previous Note (5G Basics)](https://hackmd.io/X-DW_k6rSLuy15X7YBg1iw#Radio-Access-Network)