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Broadly speaking, the ITU-T synchronisation standards can be grouped into three major categories, each of which is covered by several methods:
- Standards aimed at delivering accurate frequency, to better than 50ppb
Main use case: 2G, 3G and 4G cellular mobile radio using Frequency Division Duplexing, FDD
Methods include:- Physical layer synchronisation using Synchronous Ethernet (SyncE)
- Packet-based synchronisation using Precision Time Protocol (PTP)
- Standards aimed at delivering accurate time and phase, to better than 1.5us
Main use case: 3G and 4G cellular mobile radio using Time Division Duplexing, TDD
Methods include:- Combined PTP/SyncE, using boundary clocks (BCs) or transparent clocks (TCs) at every node in the network (full timing support, FTS)
- Combined GNSS and PTP, operating over existing networks, where not all the nodes in the network contain BCs or TCs (assisted partial timing support, APTS)
- PTP alone, operating over existing networks, where not all the nodes in the network contain BCs or TCs (partial timing support, PTS)
- Standards aimed at delivering very accurate time and phase, to better than 130ns
Main use case: 5G cellular mobile radio using co-operative processing techniques
Methods include:- Combined PTP/enhanced SyncE, using boundary clocks (BCs) or transparent clocks (TCs) at every node in the network (full timing support, FTS)
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