Distributed synchronization method and system

• US 7,860,040 B2
• Filed: 05/04/2005
• Issued: 12/28/2010
• Est. Priority Date: 05/28/2004
• Status: Expired due to Fees

• Current Assignee: Thales SA
• Original Assignee: Thales SA
• Inventors: Fachau, Laurent, Thill, Jean-Claude
• Primary Examiner(s): MIZRAHI, DIANE D
• Application Number:
  US11/569,663
• Publication Number:
  US 20070230434A1
• Time in Patent Office: 2,064 Days
• Field of Search: 370/314, 370/321, 370/322, 370/326, 370/329, 370/337, 370/348, 370/349, 370/350
• US Class Current: 370/314
• CPC Class Codes: H04J 3/0664 unidirectional timestamps
• CPC Class Codes: H04J 3/0667 Bidirectional timestamps, e.g. NTP or PTP for compensation of clock drift and for compensation of propagation delays arrangements for monitoring round trip delays in packet switching networks H04L43/0864
• CPC Class Codes: H04W 56/002 Mutual synchronization

Abstract

A distributed synchronization method in a communication network is disclosed. A number of stations exchange messages between themselves. A synchronization pattern characteristic of the clock reference of the sender is inserted into each message transmitted by a sender. The clock reference of each station is updated with the clock reference that it receives from another station of the network if, and only if, the received time is leading the clock reference. The update is done by calculating the difference ΔX=T′a−Ta between the time of sending T′a of the message received by a station A and the time of reception Ta of the same message by the station B, and applying a correction 0<ΔY<=ΔX if the received time of sending is leading by a quantity of at least τ (ΔX>τ>0).

Claims

1. A distributed synchronization method in a communication network comprising a number of stations exchanging messages between themselves, comprising the following steps:

inserting by a sender station into each message transmitted by the sender station a synchronization pattern characteristic of the clock reference of the sender station,

updating the clock reference of each station with the clock reference that each station receives from another station of the network if, and only if, the time received is in advance the clock reference, the update being done as follows;

calculating by a receiving station, the difference Δ

X=T′

a−

Ta between the time of sending T′

a of the message received by a station A and the time of reception Ta of the same message by the station B,

applying, by the receiving station, a correction 0<

Δ

Y<

=Δ

X if the received time of sending is in advance by a quantity of at least τ

(Δ

X>

τ

>

0).

2. The method as claimed in claim 1, wherein the error correction between two stations is performed as follows:

on the synchronization links set up between the different stations of the network, T₁=T′

°

a−

T°

a is calculated, being the difference between the time of sending from a station B and the time of reception of a message received by A at °

a and sent by B at T°

′

a,

A corrects T₁ by the intermediate corrections made since T°

a and the time of sending T′

a by A of a new message, to obtain Δ

T°

′

=T₁—

corrections, A transmits in the message T′

a, T′

°

a and Δ

T°

′

to the remote station concerned B,

B corrects Δ

T°

′

by the clock corrections made between T′

°

a and Ta to obtain Δ

T₃,

B determines Δ

T₂=T′

a−

Ta

if Δ

T₂−

Δ

T₃ is greater than 0, then B corrects the clock of the station with Δ

T₂−

Δ

T₃ measuring twice the advance of the remote station A corrected by the propagation times.

3. The method as claimed in claim 2, wherein each station comprises an internal clock having a drift +/−

A and the network has a driver maintaining this clock by sending pulses, the sending of the pulses is adapted to maintain the drift of the internal clock within a given range, −

B;

−

B-2A.

4. The method as claimed in claim 2, wherein the network is a radio network.

5. The method as claimed in claim 2 to a network comprising one or more stations in radio silence mode.

6. The method as claimed in claim 2 to a network having a GPS on one or more stations, the GPS clock messages being treated as received time messages.

7. The method as claimed in claim 1, wherein a station comprising an internal clock having a drift +/−

A and the network having a driver maintaining this clock by sending pulses, the sending of the pulses is adapted to maintain the drift of the internal clock within a given range.

8. The method as claimed in claim 7, wherein the range is.

9. The method as claimed in claim 8, wherein the network is a radio network.

10. The method as claimed in claim 8 to a network comprising one or more stations in radio silence mode.

11. The method as claimed in claim 7 to a network having a GPS on one or more stations, the GPS clock messages being treated as received time messages.

12. The method as claimed in claim 8 to a network having a GPS on one or more stations, the GPS clock messages being treated as received time messages.

13. The method as claimed in claim 7, wherein the network is a radio network.

14. The method as claimed in claim 7 to a network comprising one or more stations in radio silence mode.

15. The method as claimed in claim 1, wherein the network is a radio network.

16. The application of the method as claimed in claim 1 to a network comprising one or more stations in radio silence mode.

17. The application of the method as claimed in claim 1 to a network having a GPS on one or more stations, the GPS clock messages being treated as received time messages.

18. The distributed synchronization system as claimed in claim 1, comprising an external clock reference.

19. A distributed synchronization system in a network comprising a number of stations exchanging messages between themselves, comprising:

a internal clock H, the time of which is controlled by a driver and an optional delay control device, such that the drift of the time is always negative,

a device C_E/R which receives the messages and the main function of which is to measure the time of reception and control the time of sending of the messages,

a device Co for correcting the time H, receiving the clock information (T, Δ

T) transported by the messages and calculating the synchronization data to be transported, the device Co being designed to;

calculate the difference Δ

X=T′

a−

Ta between the time of sending T′

a of the message received by a station A and the time of reception Ta of the same message by the station B,

apply a correction 0<

Δ

Y<

=Δ

X if the received time of sending is in advance of by a quantity of at least τ

(Δ

X>

τ

>

0).

20. The distributed synchronization system as claimed in claim 19, wherein the network is a radio network.