System for establishing and maintaining a clock reference indicating one-way latency in a data network

• US 9,722,718 B2
• Filed: 07/19/2016
• Issued: 08/01/2017
• Est. Priority Date: 08/24/2012
• Status: Active Grant

• Current Assignee: Accedian Networks Inc. (Cisco Systems, Inc.)
• Original Assignee: Accedian Networks Inc. (Cisco Systems, Inc.)
• Inventors: Hansson, Kjell, Hagsand, Olof
• Primary Examiner(s): Lee, Andrew
• Application Number:
  US15/213,517
• Publication Number:
  US 20160329979A1
• Time in Patent Office: 378 Days
• CPC Class Codes: H04J 3/0658 Clock or time synchronisation among packet nodes
• 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: H04L 1/0018 based on latency requirement
• CPC Class Codes: H04L 43/0858 One way delays
• CPC Class Codes: H04L 43/0864 Round trip delays
• CPC Class Codes: H04L 69/22 Parsing or analysis of headers
• CPC Class Codes: H04L 7/0012 by comparing receiver clock with transmitter clock

Abstract

A method for indicating one-way latency in a data network, with continuous clock synchronization, between first and second node having clocks that are not synchronized with each other includes a continuous synchronization session and a measurement session. The method repetitively sends predetermined synchronization messages from the first node to the second node and from the second node to the first node, calculates a round trip time for each message at the first node, updates a synchronization point if the calculated round trip time is smaller than a previously calculated round trip time, stores the updated synchronization points of a synchronization window, and calculates a virtual clock from the updated synchronization points of the synchronization window. The measurement session collects multiple measurements of one-way latency between the first and second nodes using the virtual clock, and generates a latency profile by interpolating the multiple measurements.

Claims

1. A method of adapting to clock offsets in a network, the method comprising:

establishing a plurality of virtual clocks at a responding node, each of the plurality of virtual clocks associated with one of a plurality of requesting nodes;

transmitting a plurality of synchronization requests from the responding node to each of the plurality of requesting nodes;

responding to each of the plurality of synchronization requests received by each of the plurality of requesting nodes by transmitting a synchronization response back to the responding node;

for each of the plurality of synchronization responses received by the responding node, calculating a plurality of round trip delay measurements at the responding node, utilizing the plurality of round trip delay measurements to produce a plurality of synchronization points for each of the plurality of requesting nodes; and

and utilizing the round trip delay to determine a latency profile for each of the plurality of requesting nodes.

2. The method of claim 1 wherein each of the plurality of synchronization points associated with each of the plurality of requesting nodes is produced using the minimum of the plurality of round trip delay measurements between the responding node and the associated one of the plurality of requesting nodes.

3. The method of claim 1 wherein the plurality of synchronization points are periodically updated using an additional plurality of round trip delay measurements.

4. The method of claim 1 wherein the number of the plurality of synchronization requests is predetermined.

5. The method of claim 1 wherein the plurality of synchronization points is produced by calculating a sum of least-squared method.