Time synchronization in computer network

• US 20040073718A1
• Filed: 11/12/2003
• Published: 04/15/2004
• Est. Priority Date: 12/28/2000
• Status: Abandoned Application

• Current Assignee: ABB Research Ltd. (ABB Ltd.)
• Original Assignee: ABB Research Ltd. (ABB Ltd.)
• Inventors: Skeie, Tor, Lokstad, Trond, Johannessen, Svein
• Application Number:
  US10/465,944
• Publication Number:
  US 20040073718A1
• Time in Patent Office: Days
• US Class Current: 709/400
• CPC Class Codes: G04G 7/00 Synchronisation radio-controlled time-pieces G04R
• 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: H04J 3/0697 Synchronisation in a packet node
• CPC Class Codes: H04L 1/08 by repeating transmission, e.g. Verdan system H04L1/1858 and H04L1/189 take precedence
• CPC Class Codes: H04L 43/50 Testing arrangements
• CPC Class Codes: H04L 69/28 Timers or timing mechanisms used in protocols
• CPC Class Codes: H04L 69/329 in the application layer [OSI layer 7]
• CPC Class Codes: H04L 9/40 Network security protocols

Abstract

A method for improved Network Time Protocol time synchronization in a computer network (1) where the computer network comprises a time client (2) and a timeserver (3). To eliminate network access errors at the client side, the actual time of leaving is stored in the time client (2) as a special time stamp (T11) and later substituted for T1 in the calculations. To eliminate network access errors at the server side, the time request packet is duplicated and returned twice, the second time containing the time stamp when the first packet left the server (T31). To eliminate network transversal jitter when using a switched network, a packet with a multicast is used and the time stamp (T11) is taken when the time request packet is reflected back from the switch and (T31) is taken when the reply packet is reflected back from the switch.

Claims

1. A method for Network Time Protocol time synchronization in a computer network (1), the computer network comprising a time client (2) and a timeserver (3), the method comprising the steps of

generating a time request packet (4) in the time client,

time-stamping the time request packet with a first time stamp (T1) corresponding to the time the time request packet is generated,

transmitting the time request packet to the time server,

time-stamping the time request packet with a second time stamp (T2) when it arrives at the time server,

time-stamping the time request packet with a third time stamp (T3) when it is sent back to the time client, characterized by the steps of

storing the actual time the time request packet (4) leaves the time client (2) as a fourth time stamp (T11) in the time client (2), after the step of time stamping the packet with the first time stamp (T1) in the time client, and

replacing the first time stamp (T1) in the time request packet by the fourth time stamp (T11) when the time request packet has returned to the time client, in order to improve the time client accuracy.

2. A method according to claim 1,

characterized in that the computer network (1) is a Local Area Network (LAN).

3. A method according to claim 1 or 2,

characterized by the steps of

duplicating the time request packet (4) into a time correction packet (5) in the time server (2),

time-stamping the time correction packet with the actual time the time request packet leaves the time server in the form of a fifth time stamp (T31),

transmitting the time correction packet (5) back to the time client (2), and

replacing the third time stamp (T3) in the time request packet by the fifth time stamp (T31) from the time correction packet.

4. A method according to claim 1, where a store-and-forward device and/or a switching device (6) are/is in the path between the time client (2) and the timeserver (3), characterized by

using a multicast or broadcast address for the time request packet (4) when transmitting the time request packet to the time server such that the time request packet is reflected to the time server from the store-and-forward device and/or switching device, and

time-stamping the fourth time stamp (T11) in the time client (2) as the reflected time request packet returns to the time client (2) from the store-and-forward or switching device (6).

5. A method according to claim 4,

characterized by the steps of

duplicating the time request packet (4) into a time correction packet (5) in the time server (2),

time-stamping the time request packet with a third time stamp (T3) when it is sent back out using a multicast or broadcast address

time-stamping the time correction packet with the actual time the time request packet was reflected back to the time server in the form of a fifth time stamp (T31)

transmitting the time correction packet back to the time client (2) and

replacing the third time stamp (T3) in the time request packet by the fifth time stamp (T31) from the time correction packet.

6. A Method according to any of the preceding claims, characterized by time-stamping the fourth time stamp (T11) or the fifth time stamp (T31), either in a network transmit interrupt or by using a dedicated hardware timer.

7. Use of the method according to any of claims 1-6 for control and protection of an energy distribution network node.