This section describes PTP considerations for Telco Cloud RAN deployments.

PTP Design Considerations

Precision Time Protocol (PTP) delivers time synchronization in various Telco applications and environments. It is defined in the IEEE 1588-2008 standard. PTP helps issuing accurate time and frequency over telecommunication mobile networks. Precise timekeeping is a key attribute for telco applications. It allows these applications to accurately construct the precise sequence of events that occurred or occur in real time. So, each DU in the Telco Cloud RAN must be time-synchronized.

For more information about the clocking models (LLS-C1 through LLS-C4), see the Telco Cloud - RAN Domains section.

PTP is leveraged in the RAN to provide consistent clocking between the DU and the RU. This can be configured in various ways depending on the RAN clocking requirements for LLS-C3. The following configurations can be automated through Telco Cloud Automation.

  • PCI-Pass Through PTP: In this model, a dedicated port from the Network Interface Card is used to provide clocking from the cell site router into the DU network function.

  • VF-based PTP: In this model, an SR-IOV Virtual Function (VF) is used to provide clocking between the cell site router and the DU network function. The VF-based model does not require a dedicated port. Instead, the same physical port used for the fronthaul traffic is used for the PTP clock.

LLS-C1 is also supported. This model depends on the exact hardware deployed at the cell site. Some NICs support an on-board GNSS, which is connected to the external Global-Positioning-System antenna. In this mode, the cell site router is not involved in the clocking path. The RUs are connected directly to the physical server and PTP is provided directly from the DU to the RU.

Note:

As highlighted, support for LLS-C1 is dependent on the vendor hardware deployed at the cell site. Some Network Interface Cards have onboard GNSS capabilities, while other Network Interface cards do not have the onboard GNSS and require additional external components for clocking.

PTP Notification

The O-RAN working group 6 (Cloudification and Orchestration Workgroup) includes an O-Cloud Notification API specification for event consumers. Telco Cloud Platform RAN incorporates a model to support this specification.

The notification model provides a way for a consumer (CNF) to subscribe to status and event updates from the O-Cloud environment.

The CNF can subscribe to notifications through a sidecar co-located in the same pod as the DU Worker or through a local REST API. The CNF can query, register, and receive notifications through a callback API specified during the CNF registration.

The initial instantiation of the Cloud API notification framework provides notification for PTP status events. Rather than each RAN NF vendor incorporating multiple mechanisms to support multiple timing implementations, this notification framework provides a REST API for the NF vendor to subscribe and receive PTP synchronization events. The Cloud API Notification framework monitors the PTP status (PTP Sync Status and PTP Lock Status) and delivers notifications through a message bus to consumer applications.

Design Recommendation

Design Justification

Design Implication

If the consumer CNF (DU) requires event notifications, deploy and integrate the sidecar with the CNF.

Provides a way for the notification (PTP status changes) to be communicated by the O-Cloud to event consumers.

Requires integration between the CNF (DU) and the sidecar applications.

If the consumer CNF (DU) requires event notifications, the O-Cloud API CSAR must also be deployed.

Provides a mechanism for the O-Cloud to monitor PTP and communicate to the sidecar.

Increases the overall CNF count deployed

The increased CNF count must be considered when designing to scale.

Leverage a clocking solution based on the RAN requirements for LLS-C1 or LLS-C3.

Ensure proper clocking is configured between DU and RU

LLS-C3 is easier to implement, but some deployments might require LLS-C1 which in turn requires additional hardware support.