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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:

  1. 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)
  2. 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)
  3. 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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