Method and system for time synchronization
First Claim
1. A method of synchronizing a timing device of a client station comprising the steps of:
- a) sending a plurality of packets, each packet being sent at a predetermined time and having a predetermined temporal spacing from other packets, from a time server to the client station via a communications network having unknown transmission time variations;
b) receiving the plurality of packets at the client station;
c) determining a time indicative of a local time of receipt of each packet of the plurality of packets at the client station and storing time data in dependence thereon;
d) returning the plurality of packets to the time server via the communications network;
e) determining a time indicative of a local time of receipt of each packet of the plurality of packets at the time server; and
,f) determining synchronization data in dependence upon round trip delay of the packets and in dependence upon variance in temporal spacing of received packets relative to the predetermined temporal spacing, the synchronization data relating to an estimate of a minimum travel time of a packet between the time server and the client station via a communications network having unknown transmission time variations that are significant relative to the minimum travel time,wherein each packet comprises a binary signal of m bits, the binary signal comprising an identifier of the packet and an identifier of the time server.
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Accused Products
Abstract
A method for synchronizing a timing device of a client station via a communications network is disclosed. A plurality of packets is sent from a time server to the client station via the communications network. Upon receipt of the plurality of packets at the client station a time indicative of a local time of receipt of the plurality of packets is determined and the plurality of packets are returned to the time server via the communications network. Upon receipt of the plurality of packets at the time server data in dependence upon round trip delay of the packets and variance in packet spacing are determined and compared to threshold values. If the determined data are within the threshold values data indicative of a time correction are determined and sent from the time server to the client station.
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Citations
20 Claims
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1. A method of synchronizing a timing device of a client station comprising the steps of:
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a) sending a plurality of packets, each packet being sent at a predetermined time and having a predetermined temporal spacing from other packets, from a time server to the client station via a communications network having unknown transmission time variations; b) receiving the plurality of packets at the client station; c) determining a time indicative of a local time of receipt of each packet of the plurality of packets at the client station and storing time data in dependence thereon; d) returning the plurality of packets to the time server via the communications network; e) determining a time indicative of a local time of receipt of each packet of the plurality of packets at the time server; and
,f) determining synchronization data in dependence upon round trip delay of the packets and in dependence upon variance in temporal spacing of received packets relative to the predetermined temporal spacing, the synchronization data relating to an estimate of a minimum travel time of a packet between the time server and the client station via a communications network having unknown transmission time variations that are significant relative to the minimum travel time, wherein each packet comprises a binary signal of m bits, the binary signal comprising an identifier of the packet and an identifier of the time server. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method of synchronizing a timing device of a client station comprising the steps of:
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a) sending a plurality of packets, each packet being sent at a predetermined time and having a predetermined temporal spacing from other packets, from a time server to the client station via a communications network having unknown transmission time variations; b) receiving the plurality of packets at the client station; c) determining a time indicative of a local time of receipt of each packet of the plurality of packets at the client station and storing time data in dependence thereon; d) returning the plurality of packets to the time server via the communications network; e) determining a time indicative of a local time of receipt of each packet of the plurality of packets at the time server; f) determining synchronization data in dependence upon round trip delay of the packets and in dependence upon variance in temporal spacing of received packets relative to the predetermined temporal spacing, the synchronization data relating to an estimate of a minimum travel time of a packet between the time server and the client station via a communications network having unknown transmission time variations that are significant relative to the minimum travel time; g) comparing the synchronization data to threshold values; h) determining data indicative of a time correction if the determined data of step f) are within the threshold values; and
,i) sending a signal comprising the data indicative of a time correction from the time server to the client station, wherein step i) comprises the step of; signing securely at the time server the signal comprising the data indicative of a time correction. - View Dependent Claims (12)
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13. A method of synchronizing a timing device of a client station, comprising the steps of:
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a) sending a plurality of packets, each packet being sent at a predetermined time and having a predetermined temporal spacing from other packets, from a time server to the client station via a communications network having unknown transmission time variations; b) receiving the plurality of packets at the client station; c) determining a time indicative of a local time of receipt of each packet of the plurality of packets at the client station and storing time data in dependence thereon; d) returning the plurality of packets to the time server via the communications network, e) determining a time indicative of a local time of receipt of each packet of the plurality of packets at the time server; f) determining synchronization data in dependence upon round trip delay of the packets and in dependence upon variance in temporal spacing of received packets relative to the predetermined temporal spacing, the synchronization data relating to an estimate of a minimum travel time of a packet between the time server and the client station via a communications network having unknown transmission time variations that are significant relative to the minimum travel time; and
,g) providing a warning signal if the round trip delays of the packets are not within a threshold value, the threshold value being determined using a statistical estimate of round trip delays of the communications network.
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14. A method of synchronizing a timing device of a client station comprising the steps of:
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a) sending a plurality of packets, each packet being sent at a predetermined time and having a predetermined temporal spacing from other packets, from a time server to the client station via a communications network having unknown unknown transmission time variations; b) receiving the plurality of packets at the client station; c) determining a time indicative of a local time of receipt of each packet of the plurality of packets at the client station and storing time data in dependence thereon, d) returning the plurality of packets to the time server via the communications network; e) determining a time indicative of a local time of receipt of each packet of the plurality of packets at the time server; f) determining synchronization data in dependence upon round trip delay of the packets and in dependence upon variance in temporal spacing of received packets relative to the predetermined temporal spacing, the synchronization data relating to an estimate of a minimum travel time of a packet between the time server and the client station via a communications network having unknown transmission time variations that are significant relative to the minimum travel time g) comparing the synchronization data to threshold values; h) determining data indicative of a time correction if the determined data of step f) are within the threshold values; and
,i) sending a signal comprising the data indicative of a time correction from the time server to the client station, wherein step h) comprises the steps of; determining a round trip delay value for each of the plurality of packets; determining a minimum round trip delay value by interpolating using at least two round trip delay values; determining an interpolated predetermined time corresponding to the interpolated round trip delay value; and
,calculating data indicative of a correct time by adding half of the interpolated minimum round trip delay value to the interpolated predetermined time.
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15. A method of synchronizing a timing device coupled to a communications network comprising the steps of:
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a) sending a plurality of packets, each packet being sent at a predetermined time, from a first node to a second node via a communications network having unknown transmission time variations; b) receiving the plurality of packets at the second node; c) determining a time indicative of a local time of receipt of each packet of the plurality of packets and providing time data in dependence thereon; d) returning the plurality of packets to the first node via the communications network; e) determining a time indicative of a local time of receipt of each packet of the plurality of packets at the first node; and
,f) determining data in dependence upon round trip delay of the packets and variance in packet spacing and comparing the data to threshold values, the data relating to an estimate of a minimum travel time of a packet between the first node and the second node via a communications network having unknown transmission time variations that are significant relative to the minimum travel time, g) determining data indicative of a time correction if the determined data of step f) are within the threshold values, wherein the provided time data is appended to a packet and is returned with the packet to the first node.
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16. A method of synchronizing a timing device coupled to a communications network comprising the steps of:
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a) sending a plurality of packets, each packet being sent at a predetermined time, from a first node to a second node via a communications network having unknown transmission time variations; b) receiving the plurality of packets at the second node; c) determining a time indicative of a local time of receipt of each packet of the plurality of packets and providing time data in dependence thereon; d) returning the plurality of packets to the first node via the communications network; e) determining a time indicative of a local time of receipt of each packet of the plurality of packets at the first node; and
,f) determining data in dependence upon round trip delay of the packets and variance in packet spacing and comparing the data to threshold values, the data relating to an estimate of a minimum travel time of a packet between the first node and the second node via a communications network having unknown transmission time variations that are significant relative to the minimum travel time, wherein in step (c) each of the packets is time stamped with a local time of the second node.
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17. A system of synchronizing a timing device of a client station via a communications network comprising:
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first processing means connected to the communications network and a time clock; and
, second processing means connected to the communications network and the tinning device,wherein the first processing means comprise; means for sending in real time a plurality of packets, each packet being sent at a predetermined time, via the communications network to second processing means; means for receiving the plurality of packets from the second processing means in real time; means for determining in real time a time indicative of a time of receipt of each of the plurality of packets; means for determining data in dependence upon round trip delay of the packets and variance in packet temporal spacing and comparing the data to threshold values; means for determining data indicative of a correct time in dependence upon time data from the time clock and the data in dependence upon round trip delay of the packets and variance in packet temporal spacing; and
,means for sending a signal comprising the data indicative of a time correction to the second processing means via the communications network; and, wherein the second processing means comprise; means for receiving a plurality of packets from the first processing means in real time; means for determining in real time a time indicative of a time of receipt of each of the plurality of packets; means for returning the plurality of packets in real time to the first processing means; means for receiving a signal comprising the data indicative of a time correction from the first processing means; means for synchronizing the timing device in dependence upon the data indicative of the time correction; and
,means for time-stamping each of the packets in real time. - View Dependent Claims (18)
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19. A system of synchronizing a timing device of a client station via a communications network comprising:
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first processing means connected to the communications network and a time clock; and
, second processing means connected to the communications network and the timing device,wherein the first processing means comprise; means for sending in real time a plurality of packets, each packet being sent at a predetermined time, via the communications network to second processing means; means for receiving the plurality of packets from the second processing means in real time; means for determining in real time a time indicative of a time of receipt of each of the plurality of packets; means for determining data in dependence upon round trip delay of the packets and variance in packet temporal spacing and comparing the data to threshold values; means for determining data indicative of a correct time in dependence upon time data from the time clock and the data in dependence upon round trip delay of the packets and variance in packet temporal spacing; and
,means for sending a signal comprising the data indicative of a time correction to the second processing means via the communications network; and, wherein the second processing means comprise; means for receiving a plurality of packets from the first processing means in real time; means for determining in real time a time indicative of a time of receipt of each of the plurality of packets; means for returning the plurality of packets in real time to the first processing means; means for receiving a signal comprising the data indicative of a time correction from the first processing means; means for synchronizing the timing device in dependence upon the data indicative of the time correction; and
,means for attaching in real time to at least one of the packets an authenticator identifying the client station. - View Dependent Claims (20)
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Specification