Peer-to-peer transparent clocks and methods of estimating skew in peer-to-peer transparent clocks

Patent metadata

Field	Value
Publication number	US-2020021379-A1
Application number	US-201816036186-A
Country	US
Kind code	A1
Filing date	Jul 16, 2018
Priority date	Jul 16, 2018
Publication date	Jan 16, 2020
Grant date	—

Abstract

This invention relates to peer-to-peer transparent clocks and methods of estimating skew in peer-to-peer transparent clocks. Embodiments of the invention relate to techniques for estimating clock skew between a free-running clock in a transparent clock and a master clock, in particular by using the timing information embedded in timing messages passing through the transparent clock. Further embodiments of the invention set out uses of these estimates to modify the residence times computed by the transparent clock and a synchronization network including such transparent clocks.

First claim

1 . A method of estimating the skew of a local clock in a peer-to-peer transparent clock device connected in a network between a master device having a master clock and a slave device, the method including the steps of:
sending timing messages from the master device to the slave device over the network, the timing messages passing through said transparent clock device; recording times of sending of said timing messages by the master device; extracting, in the transparent clock device, from timing messages sent from the master device to the slave device, the times of sending of said timing messages; recording the times of receipt by the transparent clock device of timing messages sent from the master device to the slave device; extracting, in the transparent clock device, from the timing messages, the total delay experienced by each timing message in passing from the master device to the transparent clock device, including the residence time in other transparent clock devices between the master device and the transparent clock device; and estimating the skew of the local clock compared to the master clock using a plurality of each of said extracted and recorded times.

2 . A method according to claim 1 , further including the step of syntonizing the local clock to the master clock.

3 . A method according to claim 1 , further including the step of computing modified residence times in the transparent clock device using the estimated skew of the local clock.

4 . A method according to claim 1 wherein the step of estimating the skew of the local clock includes:
calculating the skew α as:

α
=

(

T

1
,
n

-

T

1
,

n
-
1

)

+

(

d

total
,
n

-

d

total
,

n
-
1

)

(

T

2

TC

,
n

-

T

2

TC

,

n
-
1

)

-
1

wherein 1 is the departure time of the nth timing message sent from the master device to the slave device, 2TT is the arrival time of the nth timing message sent from the master device to the slave device at the transparent clock device and is the total delay experienced by the nth timing message in passing from the master device to the transparent clock device.

5 . A method according to claim 1 wherein the step of estimating the skew of the local clock includes operating a Kalman filter using the measurement equation

X
n

=

[

θ
n

α
n

]

=

[

1

(

T

2

TC

,
n

-

T

2

TC

,

n
-
1

)

0

1

]



[

Assignees

• Khalifa Univ Of Science Technology And Research
• British Telecomm
• Emirates Telecommunications Corp

Inventors

• Aweya James

Classifications

• H04J3/0667 Primary

  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 title

• H04J3/0673

  using intermediate nodes, e.g. modification of a received timestamp before further transmission to the next packet node, e.g. including internal delay time or residence time into the packet · CPC title

• H04J3/0644 Primary

  External master-clock · CPC title

• H04J3/0682

  by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging · CPC title