# OPEN RAN

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**Resources**
1. [Introduction to Open RAN](https://www.brighttalk.com/webcast/16515/359818?utm_source=brighttalk-portal&utm_medium=web&utm_content=Parallel%20Wireless&utm_campaign=webcasts-search-results-feed)
2. [An Introduction to the Open RAN Concept by Parallel Wireless](https://www.youtube.com/watch?v=-fVHO_WCGF8)
3. [Wilfrid's notes](https://hackmd.io/8n7BZiJgRD-BrIGJ_DxkvQ)
4. [Ferlinda's notes](https://hackmd.io/@ferlinda/rkqC-jlWU)
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Wireless network comprises two domains: RAN and Core Network. The function of hardware nowadays have been replace by Commercial Off-The-Shelf Severs (COTS)

*Transport network = Backhaul*

**RAN**
- Final link between network and phone
- Visible piece (antennae on towers and base stations)
- Antenna transmits and receives signals to and from phones. The signal is digitalized in the RAN base station and conected to the network

**Core**
- Provides access controls
- Controls the network by making handovers happen as a user moves from coverage provided bye one RAN tower to the next
- Include firewall, routers, gateway, etc

## Notes
- 3GPP started the journey with Control and User Plane Separation (CUPS) of EPC nodes in 3GPP Release-14.
- CUPS provides architecture enhancements for separation of functionality in core networks --> Enable flexible network deployment and operation, by distributed or centralized deployment
- 5G Core (5GC) continues this Control & User Plane Separation with Service Based Architecture (SBA) --> SBA leverages service-based interactions between different network functions, aligning system operations with the Network Functions Virtualization (NFV) and Software Defined Networking (SDN) paradigms
- **NFV has enabled moving of hardware into software**.
- NFV Approach ---> The function of hardware nowadays have been replace by Commercial Off-The-Shelf Servers (COTS)

## DISAGGREGATION OF THE CORE NETWORK
Base station split into two part, **Baseband Unit (BBU)** and **Radio Unit (RU)**

*(Left) How mobile towers used to look in the 2G and 3G
(Right) During the later phases of 3G and during 4G rollout***

- Access network can be divided into 2 main sections, BBU and RRU
- BBU (Baseband Unit) handles the Digital Signal Processing (DSP) task
- RRU (Remote Radio Unit) handles the Radio Frequency (RF) task of the access network

- BBU hardware gets replace by the COTS server


* RRU replaced by SDR
* BBU still the same as vRAN
* Interface between SDR and BBU is an **open interface** ---> All the hardware and software work of access network (RRU, BBU, interface) dan be taken care by using vendors.
* BBU will be separated into Central Unit (CU) and Distributed Unit (DU)
* CU will handle the **less time sensitive processing functions**
* DU will handle the **real-time processing functions**

:::info
Key concept =
* Open RAN is "**opening**" the protocols and **interfaces** between these various building blocks (radios, hardware, and software) in the RAN
* Open RAN enable operators to mix and match components and goes one step further by opening the interfaces inside the base station. This will relace the specific designed hardware to a more general one
* Specific machine tends to cost less, work faster, and save more energy while a general machine will do the opposite because it has to be prepared to do everything. On the other hand, general machine will innovate faster because the software-driven development and require less money to mass-produce because the market will be bigger that specific machines.
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***RRU and DU used different vendors.***


In Open RAN, RAN is disaggregated into three main building blocks:
**1. Radio Unit (RU)**
* Where RF signals are transmitted, received, amplified, and digitized
* Located near or integrated into antenna

**2. Distributed Unit (DU)**
* Located at or near the RU
* Computation parts of the base station
* Sending digitalized radio signal into the network
* Handle less time sensitive processing functions

**3. Centralised Unit (CU)**
* Can be located nearer the Core
* Computation parts of the base station
* Sending digitalized radio signal into the network
* Handle RT processing functions

O-RAN ALLIANCE has defined different interfaces within the RAN:
- **Fronthaul** between RU and DU
- **Midhaul** between DU and CU


## WHY OPEN RAN

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- Open RAN doesn't mean Open Source
- Open RAN doesn't apply to 4G and 5G only, but also to 2G and 3G as well
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