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 ?
Trains company decided on Standard Time Zones :00pm ?

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

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

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

8. Types/Modes of Synchronization
Three different synchronization modes used
Frequency synchronization (It is also called Syntonization)
The Frequency of synchronized Network Elements is identical
No phase or Time of 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
OSI Layer 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 rules Remark: 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) (IEEE 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 Day rT = 86,400 picoseconds
One Year rT = 31,536 nanoseconds
12 Years rT = 378 microseconds
All PRS equipment must be a source based on Cesium.

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

15. Types of synchronization sources GPS – Global Positioning System
Satellites circle the earth twice a day
GPS
Receiver
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.