# Daily Note 27/07/2020
###### tags: `Daily Notes` , `O-RAN`
## Name : Christofel Rio Goenawan
## University : Bandung Institute of Technology (ITB)

---

## Schedule:
1. Study architecture of L2 Interfaces .
2. Study background ( what ? why ? how ? ) about O- CU.

## Outcome :
1. Explained detailed work of L2 Interfaces.
2. Explain the detailed background and architectures of O- CU.

## Further Plan :
- Study more detailed about O- CU Functionality
- Study more detailed about AIO Installation in Kubernets
- Try to deploy Acumos AIO in NTUST server

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## Daily Log

### 1.Study architecture of L2 Interfaces . <mark>(9.00)</mark>
- In this meeting Writer presents the progress and latest result to Prof Ray, mentors and internee.

### 2.Study background ( what ? why ? how ? ) about O- CU. <mark></mark>
- Study more detail explanation in [Documentation](https://wiki.o-ran-sc.org/display/ORANDU/O-DU+High) and other sources.

---

## Report

### 1. L2 Interfaces

>This note is continuation of Yesterday's Notes ([see here](https://hackmd.io/@christofel04/TEEP_Daily_Notes_24_7_2020)). In this note Writer use [Documentation](https://wiki.o-ran-sc.org/display/ORANDU/O-DU+High) and [Ferlinda's Note](https://hackmd.io/@ferlinda/S1iQ2--pL) as study sources.

### F1AP Handler – MAC Interface

From reference , F1AP Handler - MAC Interface consists of 4 main category as below.
1. **F1AP Handler - MAC Cell Specific API**
2. **F1AP Handler - MAC UE Specific API**
3. **F1AP Handler - MAC Cell Start message contents**
4. **F1AP handler - MAC Cell Stop message contents**

The detail can be seen as below.

#### a. F1AP Handler – MAC Cell Specific API
|Message/API |Description|
|--|--|
|Cell Start |This API is used to start the Cell at MAC, i.e., to start broadcasting the system information. MAC starts the cell at L1 before sending the confirmation to the F1AP handler.|
|Cell Stop |This API is used to stop the broadcast at MAC, i.e., to stop broadcasting the system information. MAC stops the cell at L1 before sending the confirmation to the F1AP handler. MAC may also delete the cell configuration at SCH in which case it needs to configure the SCH with|

#### b. F1AP h=Handler - MAC UE Specific APIs
Except for Report CRNTI, others are from F1AP handler to MAC.
|Message/API |Description|
|--|--|
|UE Create Request |This API adds the UE information, such as, BWP, channel information, etc, at MAC.|
|UE Reconfiguration |This API is used to reconfigure the UE information, such as, BWP, channel information, etc, at MAC. MAC returns an error if the UE has not been already added at MAC.
|UE Delete |This API is used to delete the dedicated UE information at MAC
|RACH Resource Request |This API is used to get the CRNTI, preamble information from MAC for Contention Free Random Access|
|RACH Resource Release |This API is used to release the Contention Free RACH Resources at MAC|
|UE Reset |This API is used to reset the UE associated dynamic information (eg: HARQ processes) and release the UL Control channels (PUCCH, SRS) at MAC. MAC may use invoke the API at SCH to release the UE associated resources, as above, at the SCH.|
|Get UE CRNTI |This API is used by F1AP to fetch the CRNTI of UE from MAC.|
|Report CRNTI (MAC to F1AP handler)|MAC Report CRNTI to F1AP|

#### c. F1AP Handler - MAC Cell Start message contents
|Element |Description|
|--|--|
|Cell index |Identification of the Cell|
|Frame Number |Start time|
|Slot Number |Start time|

#### d. F1AP Handler - MAC Cell Stop message contents
|Element |Description|
|--|--|
|Cell index |Identification of the Cell|
|Frame Number |Stop time|
|Slot Number |Stop time|

### F1AP Handler – RLC Interface

From reference , F1AP Handler - RIC Interface consists of 4 main category as below.
1. **F1AP Handler - RLC Specific API**
2. **F1AP Handler - RIC UE Create Message Contents**
3. **F1AP handler - RLC UE Reconfiguration message contents**
4. **F1AP handler - RLC UE Delete message contents**

The detail can be seen as below.

#### a. F1AP handler - RLC Specific APIs
|Message/API |Description|
|--|--|
|UE Create|This API is used to add the UE associated RLC entity and related information (e.g.: sn field length, t reassembly timer etc.). **Note:** One or more RLC entities of the UE may be created in the same API.|
|UE Reconfiguration|This API is used to reconfigure the UE associated RLC entity previously added at RLC. **Note:** One or more RLC entities of the UE may be reconfigured in the same API.|
|UE Delete Request|This API is used to delete the UE and associated RLC entities at RLC. **Note:** One or more RLC entities of the UE may be deleted in the same API.|
|RLC Re-establish UE Request| This API is used to re-establish all the RLC entities associated with the UE. |

#### b. F1AP handler - RLC UE Create message contents
|Element |Description|
|--|--|
|Cell index |Identification of the Cell|
|UE index |Identification of the UE|
|Frame Number |Start time|
|Slot Number |Start time|
|Number of RB |The number of RB|
|RB information list (Rb Id, logicalChannelIdentity, RB type, SN Bit, Timer)|See RLC-BearerConfig in TS 38.331|

#### c. F1AP handler - RLC UE Reconfiguration message contents
|Element |Description|
|--|--|
|Cell index |Identification of the Cell
|UE index |Identification of the UE
|Frame Number| Start time
|Slot Number| Start time
|Number of RB ToAddModList| The number of RB ToAddMod
|RB ToAddModList (Rb Id, logicalChannelIdentity,RB type, SN Bit, Timer )| See RLC-BearerConfig in 38.331|
|Number of RB ToReleaseList |The number of RB ToRelease|
|RB ToReleaseList (Rb Id) |The RB to Release|

#### d. F1AP handler - RLC UE Delete message contents
|Element |Description|
|--|--|
|Cell index| Identification of the Cell|
|UE index| Identification of the UE|
|Frame Number |Delete time|
|Slot Number |Delete time|

---

### 2. How O- CU Works?

> In this note Writer use [Documentation](https://www.o-ran.org/specification-access) and [Ferlinda's Note](https://hackmd.io/@ferlinda/SJaaKXCT8) as study sources.

There are 2 interfaces in O- DU that is **L1/L2** and **L2** Interfaces.

#### What is O- CU ?

O- RAN Central Unit ( usually called "O- CU" ) are **logical nodes that hosting RRC, SDAP and PDCP protocols in O- RAN**.
There are 2 types of O- CU as below.

1. **O- CU CP**
2. **O- CU UP**

#### O- CU Software Architecture

From reference simple O- CU Software architectures can be seen as below.


#### Interfaces Functionality

From the scheme above there are 3 interfaces used as below.

1. **F1 Interface**

F1 Interface is interface that **supports control plane and user plane separation**. It consist of 2 components, that is **F1- C** and **F1- U** interfaces. From Ferlinda's notes the functionality can be seen as below.

a. **F1- C Interfaces**
- F1 interface management function
- System Information management function
- F1 UE context management function
- RRC message transfer function
- Paging function
- Warning messages information transfer function

b. **F1- U Interfaces**
- Transfer of user data
- Flow control function

2. **O1 and E2 Interfaces**
> This interfaces have been discussed in previous study notes. [See Here](https://hackmd.io/@christofel04/TEEP2020_Daily_Notes)

#### O- CU Functional Block

The simple O- CU Functional Block scheme can be seen as below.


:::info
**Next Writer Will Study more detailed about O- CU Functional Block**
:::

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## Reference
1. https://wiki.o-ran-sc.org/display/ORANDU/O-DU+High
2. https://www.o-ran.org/specification-access
3. https://docs.o-ran-sc.org/en/latest/architecture/architecture.html