---
# System prepended metadata

title: O-RAN Open X-haul Transport
tags: [Spec]

---

# O-RAN Open X-haul Transport
###### tags: `Spec`

### Passive WDM
* Based on the end-to-end all-passive method without relay
* Disadvantages of passive WDM 
    * lack of management channel
    * weak perception of fiber link fault


![](https://i.imgur.com/lsk86ie.png)

### Active WDM

* Reduces the number of fibers
* Provide management functions between WDM equipment
* cost of Active WDM scheme is about 4-6 times higher

![](https://i.imgur.com/SNFhg06.png)

### Semi-Active WDM
* Support query, configuration, and send OAM information
* Microcontroller Unit+ power detector reduce cost
    * Support management and OAM information
![](https://i.imgur.com/PfRSJcE.png)


### DWDM Wavelength

![](https://i.imgur.com/iWhcLpz.png)
![](https://i.imgur.com/pAgAnj5.png)

### Asymmetric 
![](https://i.imgur.com/BL3l7p5.png)
![](https://i.imgur.com/AmdzCgP.png)

### Operation Administration Maintenance

* Configuration
    * Station-site shall send a configuration message to the far-end
    * response shall be sent from the far-end
* Inquiry
    * Station-site shall send an enquiry message to the far-end
    * far-end shall reply with a result message
* Active
    * need to send some state message periodically
    
![](https://i.imgur.com/nllvEdW.png)
### Passive WDM
* wavelength-ID, alarms, energy saving policy are achieved by the O-DU and the O-RU
* embedded OAM channel must allow interoperability between transceivers face to face

![](https://i.imgur.com/BWpO6rh.png)

### Active WDM
* proposed for supervision, power saving mechanism, port & wavelength-ID
* The OAM coordination between TNE and O-DU & O-RU by management system
* ![](https://i.imgur.com/U8twCFb.png)

### Semi active WDM type I
* O-RU supports the WDM transceiver
* M-Plane dedicated to OAM function control
![](https://i.imgur.com/OL6hfCO.png)

### Semi active WDM type II
* The only specific OAM function controls the wavelength assignment to achieve wavelength pairing.

![](https://i.imgur.com/d0fnyqy.png)

### Configuration
* Power configuration message
    * set the transmitting optical power
* Enquiry
    * enquiry message for the vendor information of the far end module
    * should be received by the station site within a limited time
* Active
    * keep-alive message
    * faulty condition is met, a Loss Of Signal “LOS” message should be sent immediately
    * faulty condition is met, power or temperature alarm message should be sent immediately
    * state could be sent periodically
### Xhaul Transport Network Overview
![](https://i.imgur.com/jiJbIfl.png)
### ITU-T 5G use cases
![](https://i.imgur.com/H9qznq3.png)
### Ethernet encapsulation
![](https://i.imgur.com/UDObKya.png)
### O-RAN Planes
* Control and User planes
    * between the O-RUs and their serving O-DU
    * Ethernet encapsulation is a mandatory requirement
    * IP encapsulation is optional
* Synchronization plane
    * Time Division Duplex,Carrier Aggregation
    * PTP
* Management plane
    * Hierarchical model
        * NMS only needs to interact with the O-DU level
        * between the O-DU and sub-ordinate O-RUs
    * Hybrid model
        * between the O-RU,O-DU and NMS
        * an O-RU is managed by one or more NMS
### Fronthaul logical transport requirements
* C/U-Planes
    * Ethernet connectivity from O-RUs to serving O-DU with potential backup to a redundant O-DU
    * Optional IP connectivity from O-RUs to serving O-DU with potential backup to a redundant O-DU
* S-Plane
    * Timing and Synchronization Architecture and Solutions
* M-Plane
    * Hybrid
        * IP connectivity allowing NMS to communicate with O-DUs and O-Rus
    * Hybrid or hierarchical models
        * IP connectivity allowing serving O-DU to communicate with all its sibling O-RUs
### Midhaul logical transport
* characteristics of a disaggregated gNB
    * A gNB may consist of a gNB-CU-CP, multiple gNB-CU-UPs and multiple gNB-Dus
    * DUs and CU-UPs are connected to one CU-CP via the E1 interface or the F1-C interface
    * DUs can connect to multiple CU-Ups
    * Multiple CU-UPs can connect to one CU-CP
    * For resiliency reasons, DUs and CU-UPs may connect to multiple CU-CPs

![](https://i.imgur.com/IkEqxjc.png)

### Overall Midhaul logical transport requirements
* Control Plane
    * Multi-point at the IP interfaces level (IPv4 or IPv6) between O-CU-CP and multiple O-DUs (F1-C interface).
    * Multi-point at the IP interfaces level (IPv4 or IPv6) between O-CU-CP and multiple O-CU-Ups (E1 interface).
* Data Plane
    * Multi-point at the IP interfaces level (IPv4 or IPv6) between O-CU-UP and multiple O-DUs (F1-U interface).
### O-RAN D-RAN architecture
* A 5G Distributed RAN (D-RAN) architecture, the O-CU, O-DU, and O-RU all reside at the cell site

![](https://i.imgur.com/UqyIQbK.png)
### O-RAN C-RAN architecture
* 5G Centralized RAN (C-RAN) architectures splits the radio components into discrete components 
* centralize the O-DUs or the O-DUs together with O-CU
![](https://i.imgur.com/0Y43zyS.png)
### C-RAN architecture
![](https://i.imgur.com/Nrv9Z3n.png)

### Transport slicing example
* X2 interface used between RAN nodes for non-standalone
* Xn interface is newly specified between RAN nodes in standalone operation
![](https://i.imgur.com/bL5CLiU.png)