Feed-forward time transfer mechanism for time synchronization

Patent metadata

Field	Value
Publication number	US-2016170441-A1
Application number	US-201414570232-A
Country	US
Kind code	A1
Filing date	Dec 15, 2014
Priority date	Dec 15, 2014
Publication date	Jun 16, 2016
Grant date	—

Abstract

In one embodiment, a device in a network receives a timestamp from a time synchronization master of the device that is associated with a clock message received from the master. The device determines an amount of transmission delay between the device and the master. The device generates a new clock message for one or more slaves of the device. The device determines an elapsed time between when the device received the clock message from the master and when the device generated the new clock message for the one or more slaves of the device. The device sends a new timestamp associated with the new clock message to the one or more slaves of the device. The new timestamp is based on the timestamp received from the master, the determined amount of transmission delay, and the elapsed time.

First claim

What is claimed is:

1 . A method, comprising:
receiving, at a device in a network, a timestamp from a time synchronization master of the device, wherein the timestamp is associated with a clock message received from the master; determining, by the device, an amount of transmission delay between the device and the master; generating, by the device, a new clock message for one or more slaves of the device; determining, by the device, an elapsed time between when the device received the clock message from the master and when the device generated the new clock message for the one or more slaves of the device; and sending, by the device, a new timestamp associated with the new clock message to the one or more slaves of the device, wherein the new timestamp is based on the timestamp received from the master, the determined amount of transmission delay between the device and the master, and the elapsed time between when the device received the clock message from the master and when the device generated the new clock message.

2 . The method as in claim 1 , further comprising:
calculating, by the device, the new timestamp by summing the timestamp received from the master, the determined amount of transmission delay, and the elapsed time between when the device received the clock message from the master and when the device generated the new clock message.

3 . The method as in claim 1 , wherein determining the amount of transmission delay between the device and the master comprises:
sending, by the device, a delay request message to the master; generating, by the device, a timestamp indicative of when the delay request message was sent; receiving, at the device, a delay response message from the master that includes a timestamp indicative of when the master received the delay request message; and using the timestamps indicative of when the delay request message was sent and received to compute the amount of transmission delay between the device and the master.

4 . The method as in claim 1 , wherein the master is a time synchronization grandmaster.

5 . The method as in claim 1 , wherein the device is a networking router or a networking switch.

6 . The method as in claim 1 , further comprising:
updating, by the device, a local timing mechanism of the device using the timestamp received from the master.

7 . The method as in claim 1 , wherein the clock message received from the master and the new clock message sent by the device to the one or more slaves of the device are time synchronization messages.

8 . The method as in claim 1 , further comprising:
receiving, at the device, a delay request message from a particular one of the one or more slaves; calculating, by the device, a timestamp indicative of when the device received the delay request message from the particular slave by summing the timestamp received from the time synchronization master, the amount of transmission delay between the device and the master, and an elapsed time that corresponds to the amount of time from when the device received the clock message from the master; and providing, by the device, the timestamp indicative of when the device received the delay request to the particular slave.

9 . An apparatus, comprising:
one or more network interfaces to communicate with a network; a processor coupled to the network interfaces and configured to execute one or more processes; and a memory configured to store a process executable by the processor, the process when executed operable to:
receive a timestamp from a time synchronization master of the apparatus, wherein the timestamp is associated with a clock message received from the master;
determine an amount of transmission delay between the apparatus and the master;
generate a new clock message for one or more slaves of the apparatus;
determine an elapsed time between when the apparatus received the clock message from the master and when the apparatus generated the new clock message for the one or more slaves of the apparatus; and
send a new timestamp associated with the new clock message to the one or more slaves of the apparatus, wherein the new timestamp is based on the timestamp received from the master, the determined amount of transmission delay between the apparatus and the master, and the elapsed time between when the apparatus received the clock message from the master and when the apparatus generated the new clock message.

10 . The apparatus as in claim 9 , wherein the process when executed is further operable to:
calculate the new timestamp by summing the timestamp received from the master, the determined amount of transmission delay, and the elapsed time between when the apparatus received the clock message from the master and when the apparatus generated the new clock message.

11 . The apparatus as in claim 9 , wherein the amount of transmission delay between the apparatus and the master is determined by:
sending a delay request message to the master; generating a timestamp indicative of when the delay request message was sent; receiving a delay response message from the master that includes a timestamp indicative of when the master received the delay request message; and using the timestamps indicative of when the delay request message was sent and received to compute the amount of transmission delay between the apparatus and the master.

12 . The apparatus as in claim 9 , wherein the master is a time synchronization grandmaster.

13 . The apparatus as in claim 9 , wherein the apparatus is a networking router or a networking switch.

14 . The apparatus as in claim 9 , wherein the process when executed is further operable to:
update a local timing mechanism of the apparatus using the timestamp received from the master.

15 . The apparatus as in claim 9 , wherein the clock message received from the master and the new clock message sent by the apparatus to the one or more slaves of the apparatus are time synchronization messages.

16 . The apparatus as in claim 9 , wherein the process when executed is further operable to:
receive a delay request message from a particular one of the one or more slaves; calculate a timestamp indicative of when the apparatus received the delay request message from the particular slave by summing the timestamp received from the time synchronization master, the amount of transmission delay between the apparatus and the master, and an elapsed time that corresponds to the amount of time from when the apparatus received the clock message from the master; and provide the timestamp indicative of when the apparatus received the delay request to the particular slave.

17 . A tangible, non-transitory, computer-readable media having software encoded thereon, the software when executed by a processor of a device operable to:
receive a timestamp from a time synchronization master of the device, wherein the timestamp is associated with a clock message received from the master; determine an amount of transmission delay between the device and the master; generate a new clock message for one or more slaves of the device; determine an elapsed time between when the device received the clock message from the master and when the device generated the new clock message for the one or more slaves of the device; and send a new timestamp associated with the new clock message to the one or more slaves of the device, wherein the new timestamp is based on the timestamp received from the master, the determined amount of transmission delay between the device and the master, and the ela

Assignees

• Cisco Tech Inc

Inventors

• Mcgaughey Johnston Reid

Classifications

• H04L67/125

  involving control of end-device applications over a network · CPC title

• G06F1/12 Primary

  Synchronisation of different clock signals {provided by a plurality of clock generators} · CPC title

• H04L67/01

  Protocols · CPC title