Clock model and synchronization topology in ORAN
Clock Models and Synchronization Topologies in ORAN
Open Radio Access Networks (ORAN) are revolutionizing the way cellular networks are designed and deployed. Within this complex system, maintaining precise timing and synchronization is critical for seamless operation. This article explores the different clock models and synchronization topologies considered essential for ORAN deployments.
The clock models and synchronization topologies in ORAN are crucial aspects of network design and implementation. Choosing the right topology for a specific deployment requires careful consideration of factors such as network architecture, cost, and performance requirements.? By adhering to ITU-T standards, the industry can ensure reliable and seamless operation of ORAN networks worldwide.
Why is Timing Important in ORAN?
Accurate timing across the network is fundamental for:
·???Radio Transmission Coordination: Precise timing ensures that radio signals from different cells and components are properly aligned, minimizing interference and maximizing efficiency.
·????Data Packet Transfer: Accurate timing is necessary for the efficient transmission of data packets within the network, especially in time-sensitive applications like voice calls and video streaming.
·????Regulatory Compliance: Many countries have strict regulations on the timing accuracy of cellular networks. Compliance with these regulations is essential to avoid interference with other services.
ORAN Synchronization Topologies:
To address the diverse needs of different deployments, ORAN supports multiple synchronization topologies.
Each configuration has its own characteristics and is suitable for specific scenarios. There are four scenarios:
o?? The O-DU (Open Distributed Unit) is an integral part of the synchronization chain to the O-RU (Open Radio Unit).
o?? Network timing is distributed directly from the O-DU to the O-RU via a dedicated connection.
2. Configuration LLS-C2:
o?? Similar to LLS-C1, the O-DU is part of the synchronization chain.
o?? Network timing is distributed from the O-DU to the O-RU, but Ethernet switches may be present in the fronthaul network.
o?? The allowed number of switches in the PTP and SyncE path (between PTP and SyncE master and slaves) is limited by frequency and time error contributions by all clocks in the chain.
o?? With Full Timing Support and Annex H detailed budget split, the allowed network noise limit in the budget can be met by 2 T-BC Class B switches.
o?? Additional T-BC switches may be allowed if total noise limit can be met.
o?? T-TC switch is also allowed as T-BC replacement with the same expectation based on G.8271.1.
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o?? Interconnection among switches and fabric topology (for example mesh, ring, tree, spur etc.) are deployment decisions which are out of the scope of this O-RAN spec.
3. Configuration LLS-C3:
o?? The O-DU is not part of the synchronization chain to the O-RU.
o?? Network timing is distributed directly from a PRTC/T-GM (Primary Reference Time Clock/Grandmaster Clock) to the O-RU, often from a central site.
4. Configuration LLS-C4:
o?? The O-RU is synchronized without relying on the transport network, typically using a local GNSS (Global Navigation Satellite System) receiver.
o?? O-RAN maintains network timing distribution as the preferred approach within the fronthaul network, however, there could be some deployment use cases that prevent the fronthaul network (or only a section of the network) from being upgraded to G.8271.1 compliance and meeting the target performance at the O-RU
Key Points:
?1. Clock Types and Classes: ORAN considers specific clock types and classes as defined by ITU-T (International Telecommunication Union Telecommunication Standardization Sector) standards.
??2. O-DU Synchronization: How the O-DU itself is synchronized is not a part of the topology classification. It can be synchronized from either a local or remote PRTC.
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