Maintaining a global time reference among a group of networked devices

• US 7,035,246 B2
• Filed: 03/13/2001
• Issued: 04/25/2006
• Est. Priority Date: 03/13/2001
• Status: Expired due to Term

• Current Assignee: Longhorn Automotive Group LLC (Alpha Alpha Intellectual Partners LLC)
• Original Assignee: Pulse-Link Incorporated
• Inventors: Taylor, James L.
• Primary Examiner(s): Pezzlo, John
• Assistant Examiner(s): Cho, Hong Sol
• Application Number:
  US09/805,735
• Publication Number:
  US 20020131398A1
• Time in Patent Office: 1,869 Days
• Field of Search: 370/350, 370503-507, 370/509, 370/512, 370510-523, 455/502, 375/242, 375/340, 710/25, 713/400, 713/401
• US Class Current: 370/350
• CPC Class Codes: H04J 3/0632 Synchronisation of packets and cells, e.g. transmission of voice via a packet network, circuit emulation service [CES] queuing arrangements in packet switching elements H04L49/90; synchronising systems for the synchronous transmission of a pulse code modulated video signal with one or more other pulse code modulated signals H04N7/56
• CPC Class Codes: H04J 3/0641 Change of the master or reference, e.g. take-over or failure of the master
• CPC Class Codes: H04L 2007/047 using a sine signal or unmodulated carrier
• CPC Class Codes: H04L 7/041 using special codes as synchronising signal
• CPC Class Codes: H04N 21/4305 Synchronising client clock from received content stream, e.g. locking decoder clock with encoder clock, extraction of the PCR packets arrangements for synchronising receiver with transmitter by comparing receiver clock with transmitter clock H04L7/0012; arrangements for synchronising receiver with transmitter wherein the receiver takes measures against momentary loss of synchronisation H04L7/0083
• CPC Class Codes: H04N 21/43615 Interfacing a Home Network, e.g. for connecting the client to a plurality of peripherals home Audio Video Interoperability [HAVI] data switching networks H04L12/2805
• CPC Class Codes: H04W 92/18 between terminal devices

Abstract

Synchronization is maintained among a plurality of network devices having local clocks that participate in a network. A first packet is broadcast from a first network device to other network devices that participate in the network. The first packet includes a global time reference derived from the local clock of the first network device. The clocks of the network devices that receive the first packet are adjusted to be closer to the local clock of the first network device. A first network local time reference and a second network local time reference may be maintained for a device that participates in a first network and a second network. A free running clock is maintained on the device. The difference between the free running clock and a first network global time reference is determined. A first network offset is calculated to account for the difference between the free running clock and the first network global time reference. The difference between the free running clock and a second network global time reference is determined. A second network offset is calculated to account for the difference between the free running clock and the second network global time reference.

Claims

1. A method of maintaining synchronization among a plurality of network devices having local clocks that participate in a network comprising:

broadcasting a first packet from a first network device to other network devices that participate in the network wherein the first packet includes a global time reference derived from the local clock of the first network device; and

adjusting the clocks of the network devices that receive the first packet to be closer to the local clock of the first network device;

wherein the global time reference includes a least significant part of the local clock of the first network device and does not include a most significant part of the local clock of the first network device.

2. A method of maintaining synchronization among a plurality of network devices having local clocks that participate in a network comprising:

broadcasting a first packet from a first network device to other network devices that participate in the network wherein the first packet includes a global time reference derived from the local clock of the first network device; and

adjusting the clocks of the network devices that receive the first packet to be closer to the local clock of the first network device;

wherein the global time reference includes a least significant part of the local clock of the first network device and does not include a most significant part of the local clock of the first network device, and wherein the most significant part of one of the network device local clocks is broadcast periodically and the most significant parts of all local clocks are conformed to the broadcast most significant part.

3. A method of maintaining synchronization among a plurality of network devices having local clocks that participate in a network comprising:

broadcasting a first packet from a first network device to other network devices that participate in the network wherein the first packet includes a global time reference derived from the local clock of the first network device; and

adjusting the clocks of the network devices that receive the first packet to be closer to the local clock of the first network device;

wherein adjusting the clocks of the network devices that receive the first packet to be closer to the local clock of the first network device includes adjusting the clocks of the network devices by approximately one half the difference between the broadcast global time reference and the unadjusted value of the clock being adjusted.

4. A method of maintaining synchronization among a plurality of network devices having local clocks that participate in a network comprising:

broadcasting a first packet from a first network device to other network devices that participate in the network wherein the first packet includes a global time reference derived from the local clock of the first network device; and

adjusting the clocks of the network devices that receive the first packet to be closer to the local clock of the first network device;

wherein adjusting the clocks of the network devices that receive the first packet to be closer to the local clock of the first network device includes adjusting the clocks of the network devices according to a nonlinear function of the difference between the unadjusted value of the clock being adjusted and the broadcast global time reference.

5. A method of maintaining synchronization among a plurality of network devices having local clocks that participate in a network comprising:

broadcasting a first packet from a first network device to other network devices that participate in the network wherein the first packet includes a global time reference derived from the local clock of the first network device; and

adjusting the clocks of the network devices that receive the first packet to be closer to the local clock of the first network device;

wherein adjusting the clocks of the network devices that receive the first packet to be closer to the local clock of the first network device includes adjusting the clocks of the network devices according to a nonlinear function of the difference between the unadjusted value of the clock being adjusted and the broadcast global time reference, and wherein the nonlinear function of the difference between the unadjusted value of the clock being adjusted and the broadcast global time reference causes substantially no adjustment to the clock being adjusted when the difference between the unadjusted value of the clock being adjusted and the broadcast global time reference is greater than a maximum adjustable difference.