Enhanced pulse assisted time synchronization protocol

• US 8,806,063 B1
• Filed: 07/11/2011
• Issued: 08/12/2014
• Est. Priority Date: 07/11/2011
• Status: Active Grant

• Current Assignee: Juniper Networks Incorporated
• Original Assignee: Juniper Networks Incorporated
• Inventors: Kamath, Prakash, Mehta, Apurva, Gopalakrishnan, Kamatchi, Subbiah, Rajagopalan, Puri, Rohit, Bobade, Vikram
• Primary Examiner(s): Divecha, Kamal
• Assistant Examiner(s): TURRIATE GASTULO, JUAN CARLOS
• Application Number:
  US13/180,286
• Time in Patent Office: 1,128 Days
• Field of Search: 709/248
• US Class Current: 709/248
• CPC Class Codes: G06F 1/12 Synchronisation of different clock signals provided by a plurality of clock generators
• CPC Class Codes: G06F 1/14 Time supervision arrangements, e.g. real time clock
• 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

Abstract

A network device may include a timing module and at least one interface. The timing module determines a local time of the network device indicating when the network device sends a synchronization start message. The at least one interface sends the synchronization start message to a time client device to set the current time of day on the time client device, receives a synchronization response message from the time client device indicating that the current time of day of the time client device was set, and sends a synchronization success message to the time client device indicating that the time client device has correctly set its current time of day.

Claims

1. A method comprising:

sending, with a time server, a synchronization start message to a time client device to set a current time of day on the time client device, wherein the synchronization start message includes a local time of the time server indicating when the time server sent the synchronization start message;

receiving, with the time server, a synchronization response message from the time client device indicating that the time client device received the synchronization start message and performed an operation of setting the current time of day of the time client device based on the local time of the time server as included within the synchronization start message, wherein the synchronization response message includes a local time of the time client device indicating when the synchronization response message was sent by the time client device after setting the current time of day at the time client device, wherein the local time of the time client device indicating when the synchronization response message was sent by the time client device is different than a time at which the time client device received the synchronization start message;

determining, with the time server, a local time of the time server indicating when the time server received the synchronization response message;

receiving, with the time server, a primary reference time, wherein the local time of the time server indicating when the time server sent the synchronization start message and the local time of the time server indicating when the time server received the synchronization response message are based on the primary reference time;

phase shifting, with a clock generator of the time server, at least one of a rising or falling edge of a clock signal of the time server based on the primary reference time such that the at least one of the rising or falling edge occurs at a time subsequent to the primary reference time;

determining, with the time server, the time difference between the local time of the time server indicating when the time server received the synchronization response message and the local time of the time client device as set based on the local time of the time server as included in the synchronization response message indicating when the synchronization response message was sent by the time client device; and

when the time server determines that the time difference is less than a threshold amount of time, sending, with the time server, a synchronization success message to the time client device indicating that the time client device has correctly set its current time of day.

2. The method of claim 1, wherein the threshold amount of time is one second.

3. The method of claim 1, wherein the primary reference time comprises a first unit seconds portion, and a first fractional portion of the first unit seconds portion, wherein the time subsequent to the primary reference time comprises a second unit seconds portion, and a second fractional portion of the second unit seconds portion, wherein the second unit seconds portion comprises a value that is a next consecutive value of the first unit seconds portion, and wherein the second fractional portion of the second unit seconds portion comprises a value of zero.

4. The method of claim 1, wherein the local time of the time server indicating when the time server sent the synchronization start message, the local time of the time client device as included in the synchronization response message, and the local time of the time server indicating when the time server received the synchronization response message each comprise unit seconds portions and fractional portions of the unit seconds portions.

5. The method of claim 1, wherein the time server comprises a first line card of a router, and wherein the time client device comprises a second line card of the router.

6. A method comprising:

receiving, with a time client device, a synchronization start message from a time server, wherein the synchronization start message includes a local time of the time server indicating when the synchronization start message was sent by the time server;

setting, with the time client device, a current time of day of the time client device based on the local time of the time server as included within the synchronization start message, wherein setting the current time of day comprises;

(i) when a fractional portion of a unit seconds portion of a local client time when the time client device received the synchronization start message is greater than a fractional portion of a unit seconds portion of the local time of the time server as included within the synchronization start message, setting the current time of day of the time client device using a same value of the unit seconds portion of the local time of the time server as included within the synchronization start message, and

(ii) when the fractional portion of the unit seconds portion of the local client time when the time client device received the synchronization start message is less than the fractional portion of the unit seconds portion of the local time of the time server as included within the synchronization start message, setting the current time of day of the time client device by adding one second to the value of the unit seconds portion of the local time of the time server as included within the synchronization start message;

after setting the current time of day of the time client device, sending, with the time client device, a synchronization response message to the time server to indicate that the current time of day of the time client device was set based on the local time of the time server as included within the synchronization start message, wherein the synchronization response message includes a local time of the time client device indicating when the time client device sent the synchronization response message; and

receiving, with the time client device, a synchronization success message from the time server when the time server determines that the difference between the local time of the time client device as included in the synchronization response message and a local time of the time server indicating when the time server received the synchronization response message is less than one second, wherein the synchronization success message indicates that the time client device has correctly set its current time of day.

7. The method of claim 6, wherein the local time of the time server indicating when the synchronization start message was sent by the time server, the current time of day of the time client device, and the local time of the time client device indicating when the time client device sent the synchronization response message each comprise unit seconds portions and fractional portions of the unit seconds portions.

8. The method claim 6, further comprising receiving, with the time client device, a clock signal from a clock generator of the time server, wherein determining the current time of day of the time client device and the local time of the time client device indicating when the time client device sent the synchronization response message comprises determining the current time of day of the time client device and the local time of the time client device indicating when the time client device sent the synchronization response message based on the clock signal.

9. The method of claim 6, wherein the time client device comprises a first line card of a router, and wherein the time server comprises a second line card of the router.

10. A network device comprising:

a timing module that determines a local time of the network device indicating when the network device sends a synchronization start message;

at least one interface that sends the synchronization start message to a time client device to set a current time of day on the time client device, receives a synchronization response message from the time client device indicating that the client device received the synchronization start message and performed an operation of setting the current time of day of the time client device based on the local time of the network device as included within the synchronization start message indicating when the network device sent the synchronization start message, and sends a synchronization success message to the time client device indicating that the time client device has correctly set its current time of day,

wherein the synchronization response message includes a local time of the time client device indicating when the synchronization response message was sent by the time client device,

wherein the at least one interface receives a primary reference time, and wherein the timing module determines the local time of the network device indicating when the network device sent the synchronization start message and a local time of the network device indicating when the network device received the synchronization response message based on the primary reference time; and

a clock generator that delivers a clock signal, wherein the clock generator phase shifts at least one of a rising or falling edge of the clock signal such that the at least one of the rising or falling edge occurs at a time subsequent to the primary reference time,

wherein the timing module determines a time difference between the local time of the network device indicating when the network device received the synchronization response message and the local time of the time client device as set based on the local time of the time server as included in the synchronization response message indicating when the synchronization response message was sent by the time client device, and wherein the interface sends the synchronization success message when the timing module determines that the time difference is less than a threshold time value.

11. The network device of claim 10, wherein the threshold time value is one second.

12. The network device of claim 10, wherein the primary reference time comprises a first units seconds portion, and a first fractional portion of the first units seconds portion, wherein the time subsequent to the primary reference time comprises a second units seconds portion, and a second fractional portion of the second units seconds portion, wherein the second units seconds portion comprises a value that is a next consecutive value of the first units seconds portion, and wherein the second fractional portion of the second units seconds portion comprises a value of zero.

13. The network device of claim 10, wherein the local time of the network device indicating when the network device sends the synchronization start message, the local time of the time client device as included in the synchronization response message, and the local time of the network device indicating when the network device received the synchronization response message each comprise unit seconds portions and fractional portions of the unit seconds portions.

14. The network device of claim 10, wherein the network device comprises a first line card of a router, and wherein the time client device comprises a second line card of the router.

15. A network device comprising:

at least one interface that receives a synchronization start message from a time server, wherein the synchronization start message includes a local time of the time server indicating when the synchronization start message was sent by the time server; and

a timing module that sets a current time of day of the network device based on the local time of the time server as included within the synchronization start message, and determines a local time of the network device indicating when the network device sends a synchronization response message, wherein the timing module sets the current time of day by;

(i) when a fractional portion of a unit seconds portion of a local client time when the time client device received the synchronization start message is greater than a fractional portion of a unit seconds portion of the local time of the time server as included within the synchronization start message, setting the current time of day of the time client device using a same value of the unit seconds portion of the local time of the time server as included within the synchronization start message, and

(ii) when the fractional portion of the unit seconds portion of the local client time when the time client device received the synchronization start message is less than the fractional portion of the unit seconds portion of the local time of the time server as included within the synchronization start message, setting the current time of day of the time client device by adding one second to the value of the unit seconds portion of the local time of the time server as included within the synchronization start message,

wherein after setting the current time of day of the time client device, the at least one interface sends the synchronization response message to the time server to indicate that the current time of day of the network device was set based on the local time of the time server as included within the synchronization start message, and wherein the synchronization response message includes the local time of the network device indicating when the network device sends the synchronization response message, and

wherein the at least one interface receives a synchronization success message from the time server when the time server determines that the difference between the local time of the network device as included in the synchronization response message and a local time of the time server indicating when the time server received the synchronization response message is less than one second, wherein the synchronization success message indicates that the network device has correctly set its current time of day.

16. The network device of claim 15, wherein the local time of the time server indicating when the synchronization start message was sent by the time server, the current time of day of the network device, and the local time of the network device indicating when the network device sent the synchronization response message each comprise unit seconds portions and fractional portions of the unit seconds portions.

17. The network device of claim 15, wherein the timing module receives a clock signal from the time server, and wherein the timing module sets the current time of day of the network device and determines the local time of the network device indicating when the network device sends the synchronization response message based on the clock signal.

18. The network device of claim 15, wherein the network device comprises a first line card of a router, and wherein the time server comprises a second line card of the router.