Method for synchronization in a local area network including a store-and-forward device

• US 20040151125A1
• Filed: 11/12/2003
• Published: 08/05/2004
• Est. Priority Date: 12/28/2000
• Status: Active Grant

• Current Assignee: ABB Research Ltd. (ABB Ltd.)
• Original Assignee: ABB Research Ltd. (ABB Ltd.)
• Inventors: Johanssen, Svein, Apneseth, Christoffer, Skeie, Tor, Holmeide, Oyvind, Lokstad, Trond
• Granted Patent: US 8,291,105 B2
• Time in Patent Office: Days
• US Class Current: 370/252
• 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 43/50 Testing arrangements

Abstract

The present invention relates to a method for identifying inaccurate time measurements in a local area network. The local area network comprises a sending device (2), such as a time client, a destination device (3), such as a timeserver, and a switching device and/or a store-and-forward device (6). A time request packet (4) is rejected if it arrives at the time client or timeserver within a given or calculated minimum distance from the preceding network packet. The time request packet (4) is also rejected if it falls outside a set of calculated error limits based on a set of estimates. Those estimates are kept in the time client memory and updated according to a given set of rules.

Claims

1. Method for identifying inaccurate time measurements when running time synchronization on a local area network, the local area network comprising a sending device (2), a destination device (3) and a switching device and/or a store-and-forward device (6) arranged on a path (1) between the sending device (2) and the destination device (3), characterized by

rejecting time request packets (4) that arrive to the destination device (3) within a given time interval t from a preceding network packet.

2. Method for identifying inaccurate time measurements when running time synchronization on a local area network, the local area network comprising a sending device (2), a destination device (3) and a switching device and/or a store-and-forward device (6) arranged on a path (1) between the sending device (2) and the destination device (3), characterized by

keeping one or more estimates of the accuracy and precision of the local time-of day clock in a memory in the sending device (2) and accepting or rejecting the new time measurement based on a set of calculations made from these estimates.

3. Method according to claim 2, characterized in that the sending device (2) is a time client.