# Assignment3
###### tags: `Wireless Communications course`

 p.8
reference:https://www.5gamericas.org/wp-content/uploads/2020/07/Security-Considerations-for-the-5G-Era-2020-WP-Lossless.pdf

* 前傳是指BS到DU那條

## Overview of O-RAN Fronthaul Specifications
reference:https://www.docomo.ne.jp/english/binary/pdf/corporate/technology/rd/technical_journal/bn/vol21_1/vol21_1_007en.pdf
:::success
原先不懂的
p.2

* This state of affairs has made it difficult to achieve interoperability between baseband processing equipment and radio equipment from different vendor
* 因為不同廠牌之間的技術不相容

p.3
* There is no need to transmit on the fronthaul an IQ sampling sequence for a frequency resource transmitting no signals on the DL wireless interface.
* (digital conversion)無線電波轉成數位訊號
:::

### C-RAN architecture
* Fronthaul使用光纖(optical fiber connections)
* Centralized RAN (C-RAN) connects a baseband processing section in centralized base station equipment to multiple units of radio equipment via fronthaul
* Baseband(O-DU)processing:準備好低頻訊號(data)
* radio equiment(O-RU):把準備好的低頻訊號(data)放在高頻載波上打出去

* 與RAN的差別
* CRAN把baseband拉到同一個部分
### 為甚麼要增加the required fronthaul transmission bandwidth
* (1)wider frequency bandwidths in the 5G era
* (2)higher antenna counts due to Massive Multiple Input Multiple Output (Massive MIMO)

### Split Option 7-2x is a specification for functional splitting between O-RAN Distributed Unit (O-DU) and O-RAN Radio Unit (O-RU) as following figure.

* DownLink
* resource element mapping then resulting in an IQ sampling sequence of an Orthogonal Frequency Division Multiplexing (OFDM) signal in the frequency domain,then converted to an OFDM signal in the time domain, and finally converted to an analog signal.

* UpLink
* in the UpLink (UL) process flow, the OFDM signal in the time domain received at the O-RU and converted to a digital signal is subjected to FFT processing resulting in an IQ sampling sequence of the OFDM signal in the frequency domain

* Resource element demapping:
* A process for extracting an IQ signal sequence from an IQ signal mapped to time/frequency resources in LTE, LTE-Advanced, and NR

* User bit sequence:
* The baseband bit sequence of user data

* MIMO spatial stream:
* 用超過一根天線的方式來做通訊,可以好對抗環境干擾,同時可以傳超過一份資料

### Tradeoffs in O-DU and O-RU functional splitting

* In general, the required fronthaul bandwidth becomes smaller as more functions become entrusted to the O-RU(O-RU不做事所以要把東西傳回去給O-DU做 所以 Required fronthaul bandwidth is large)
* For example, compared to CPRI in which the O-RU handles only the RF function section, placing IFFT/FFT processing in the O-RU can prevent an increase in the fronthaul required bandwidth caused by oversampling applied to the OFDM signal in the time domain.
* For example placing DL precoding in the ORU can prevent an increase in the required fronthaul bandwidth that occurs when the number of MIMO spatial streams is greater than the number of MIMO layers.
*

### p.5主要在介紹前傳的三個平面的protocol stack
* In the C/U-Plane, the O-RAN fronthaul specifications support a protocol stack that transmits signals used by eCPRI or Radio over Ethernet (RoE) directly over Ethernet and an optional protocol stack that transmits the signals over User Datagram Protocol (UDP)/IP.

* In the S-Plane, meanwhile, the O-RAN fronthaul specifications support a protocol stack that transmits signals used in Precision Time Protocol and Sync over Ethernet.
* NETCONF:is a general-purpose protocol for managing network devices

* Finally, in the M-Plane, the O-RAN fronthaul specifications support a protocol stack that transmits signals used in NETwork CONFiguration protocol (NETCONF) over Ethernet/IP/Transmission Control Protocol (TCP)/Secure SHell (SSH).

### C/U plane
* U-Plane message frame format
* The eCPRI payload of the U-Plane message can be used to transmit an IQ sample sequence of the OFDM signal in the frequency domain.
* The frame format of the U-Plane message is used in common in both directions, that is, for transmission from the O-DU to O-RU and transmission from the O-RU to O-DU

* C-Plane message

* The frame format for a C-Plane message is shown in Figure 7. The eCPRI header in a C-Plane message is the same as that of the U-Plane message
* Here, the C-Plane message source and destination identifiers have become ecpriRtcid in contrast to ecpriPcid of the U-Plane message(不同)

* The O-RU uses "BF weights" to generate a beam for transmitting and receiving signals on the radio interface.

* Using a beam identifier can be applied to digital BF, analog BF, or a combination of the two (hybrid BF)

## Delay management(我不會)


* The O-DU, meanwhile, must transmit a C/U-Plane message to the fronthaul so that it is delivered within the O-RU receive window

## S plane
* As an S-Plane, O-RAN fronthaul specifications support protocols such as PTP and SyncE to achieve high-accuracy synchronization on the O-RU side by synchronizing with the clock on the high-performance O-DU side

## M plane

* The M-Plane provides a variety of O-RU management functions to set parameters on the O-RU side as required by the C/U-Plane and S-Plane described above, to manage O-RU software (SW), perform fault management, etc.

* In the M-Plane, the O-DU and Network Management System (NMS) are specified as network devices managing O-RUs.

* Two kinds of architecture
* Hierarchical model: an O-RU is managed by one or more O-DUs.this model has the advantage of enabling network construction without affecting the existing system since O-DU supports NETCONF in this M-Plane
* Hybrid model: an O-RU is managed by one or more NMSs in addition to O-DUs.


* 
* “Start up” installation
* specifies the establishment of M-Plane connections between ORU and NETCONF clients such as O-DU and NMS. Establishing these connections on the M-Plane requires mutual exchange of Transport Layer address*46 information.
* Manual setting of Tr • ansport Layer addresses
* Allocation of Transport Layer addresses by a Dynamic Host Configuration Protocol (DHCP) server
* Allocation of Transport Layer addresses by StateLess Address Auto-Configuration (SLAAC)
* SW management
* An O-DU/NMS NETCONF client performs O-RU SW management via the M-Plane.
* 
* in the SW inventory step, the NETCONF client gets information on what types of files are currently stored on the O-RU

* Configuration management
* an O-DU/NMS NETCONF client sets O-RU parameters required on the C/U-Plane and S-Plane and gets equipment status information via the M-Plane.

* Fault management
* An NETCONF client manages O-RU faults via the M-Plane
* In this function, the O-RU sends a notification to the O-DU/NMS NETCONF client using "notification" specified as a standard message in NETCONF.
* Including:
* ID
* Location of fault occurrence
* Locations affected by fault
* Severity of fault
* New fault occurrence or a fault that has already been resolved

## advantage of L2 switch

* case(1):L2 switches之間只需要一條線路,所以cost down.
* case(2):如果有一條path fail,可以透過另外一條傳輸
* case(3):如果O-DU的port有限制的話,那透過L2 switch就可以接到很多O-RU