# 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


### Active WDM

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


### Semi-Active WDM
* Support query, configuration, and send OAM information
* Microcontroller Unit+ power detector reduce cost
* Support management and OAM information

### DWDM Wavelength


### Asymmetric

### 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

### 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


### Active WDM
* proposed for supervision, power saving mechanism, port & wavelength-ID
* The OAM coordination between TNE and O-DU & O-RU by management system
* 

### Semi active WDM type I
* O-RU supports the WDM transceiver
* M-Plane dedicated to OAM function control

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


### 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
### ITU-T 5G use cases
### Ethernet encapsulation
### 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


### 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

### 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
### C-RAN architecture

### Transport slicing example
* X2 interface used between RAN nodes for non-standalone
* Xn interface is newly specified between RAN nodes in standalone operation