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Introduction to Synchronization

Learn about synchronization and its importance in coordinating events for the seamless operation of a system. Explore different synchronization modes and options, as well as accurate synchronization sources such as atomic clocks and GPS receivers.

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Introduction to Synchronization

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  1. Introduction to Synchronization Nir Tshobani– Focus Telecom

  2. What is Synchronization ? Synchronization*is the coordination of events to operate a system in unison. The conductor of an orchestra keeps the orchestra synchronized or in time. *Wikipedia

  3. What is Time ? Well …. That is a philosophical question …. What we do care is how to synchronize it !

  4. Standard Time Definition What is the time now ? What is the time in NY now ? What was the time in NY 30.05.1883 ? Trains company decided on Standard Time Zones 18.11.1883 12:00pm ?

  5. Standard Time Definition 19.03.1918 – US Standard Time Law Great Western Railway 1840 Britain 1847 GMT – Greenwich Mean Time 02.08.1880 – Britain Standard Time Law

  6. Time Units Day/Night Seasons Days/Weeks/Months Years Seconds/Minutes/Hours

  7. Time Units -3 1 millisecond = 0.001 = 10 1 microsecond = 0.000001 = 10 1 nanosecond = 0.000000001 = 10 1 picosecond = 0.000000000001 = 10 1 Femtosecond = 0.000000000000001 = 10 1 Attosecond= 0.000000000000000001 = 10 -6 -9 -12 -15 -18

  8. Types/Modes of Synchronization • Three different synchronization modes used • Frequency synchronization (It is also called Syntonization) • The Frequencyof synchronized Network Elements is identical • No phase or Timeof day synchronization • This synchronization mode is used e.g. PDH, SDH, SyncE, GSM, UMTS-FDD and LTE-FDD • Phase synchronization • Frequency and Phase of synchronized Network Elements is identical • No Time of day synchronization • This synchronization mode is used e.g. most TDD variants • Time synchronization • Frequency, Phase and Time of day of synchronized Network Elements is identical • This synchronization mode is used e.g. some TDD variants (CDMA, LTE-TDD, LTE-A, 5G)

  9. Types/Modes of Synchronization Three different synchronization modes are used :

  10. Synchronization options • Multiple synchronization options depending on the OSI layer • Depending on the requirements and the network design synchronization can be done on different OSI layer • OSILayer 1 • Widely used for frequency synchronization • Phase and/or Time synchronization typically not possible • High reliability and accuracy • Network support required • OSI Layer 2 or 3 • Frequency synchronization without network support possible under consideration of some rulesRemark: Can have some restriction on reliability and accuracy • Phase and/or Time synchronization possible but typically need on-path support by Network Elements on the transmission path

  11. Synchronization options - Examples • OSI Layer 1 • 2 MHz, 10 MHz • 1 PPS (1 Pulse Per Second) • SDH / PDH (Signals with or without data transmission) • Synchronous Ethernet (Transmission Clock on Ethernet is synchronized) • NTR over DSL (Network Timing Reference) • GPON (It is on Layer 1 TDM based) • OSI Layer 3 or higher • PWE3 (PseudoWire Emulation Edge to Edge) e.g. CESoPSN(vendor specific solutions for clock synchronization, ToD not supported) • NTP (Network Timing Protocol) • PTP (Precision Time Protocol) (IEEE1588-2008 needed for this purpose) • GNSS (Global Navigation Satellite System). GPS, GLONASS Galileo and Beidou/Compass.

  12. Types of synchronization sources Atomic Clock • Type of clock that uses an atomic resonance, accurate, measurable reference signal generators. • In 1967 it was decided that the Cesium atom sets the international unit of time, Its frequency is accurately : 9,192,631,770Hz • For civil use there is another time scale called UTC (Coordinated Universal Time). The standard was defined by the National Institute of Standards and Technology (NIST), in the USA • The UTC accuracy is maintained by the organization of national laboratories for physics called BIPM(Bureau International des Poids et Mesures)

  13. Primary Reference Source (PRS) - Cesium CESIUM with frequency offset of 1x10-12 or an average rT/T of 1 picosecond/second One DayrT = 86,400 picoseconds One YearrT = 31,536 nanoseconds 12 YearsrT = 378 microseconds All PRS equipment must be a source based on Cesium.

  14. Types of synchronization sources Atomic Clock MHM 2010 - Hydrogen Masers 5071A - Cesium 10-15 CSAC (Chip Scale Atomic Clock) 10-13 Rb(MAC) 5x10-11 5x10-11

  15. Types of synchronization sources GPS Receiver GPS – Global Positioning System Satellites circle the earth twice a day • The GPS system is based on a 24 to 31 dedicated satellites launched by United States Department of Defense, which operates the system. • Orbiting the earth in orbit about 20,000 miles tall • The satellites revolve around the Earth and transmit time signal to the ground receiver that picks it up from four or more satellites.

  16. Summary • Synchronization is the coordination of events to operate a system in unison. • There are 3 types of Synchronization – Frequency, Phase and Time. • Atomic clocks and GPS/Glonass are the most accurate synchronization sources.

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