Method to improve the resolution of time measurements and alignment in packet networks by time modulation
First Claim
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1. A method of recovering timing information over multiple asynchronous packet networks, each having its own time grid, comprising:
- transmitting timestamped packets between a sender on a first said network and a receiver on a second said network;
transporting timing information between the sender and receiver as a modulated signal comprising a modulation in the rate of sending out the timestamped packets transmitted between the sender and receiver;
extracting said timing information from the packets arriving at the receiver; and
using said timing information at the receiver to align the time grid at the receiver with the time grid at the sender; and
wherein said modulated signal is manifested as an offset in the rate of transmission of packets from the sender, said offset being an odd fraction ƒ
of a cycle of a clock signal such that the timing error at the receiver contains only high frequency components, and wherein the packet rate is offset by an amount equal to the ratio of the packet cycle and clock cycle multiplied by ƒ
.
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Abstract
A method of recovering timing information in a packet network is disclosed wherein a modulation scheme is used to transport additional information required for clock recovery between the sender and receiver across the network.
23 Citations
18 Claims
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1. A method of recovering timing information over multiple asynchronous packet networks, each having its own time grid, comprising:
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transmitting timestamped packets between a sender on a first said network and a receiver on a second said network; transporting timing information between the sender and receiver as a modulated signal comprising a modulation in the rate of sending out the timestamped packets transmitted between the sender and receiver; extracting said timing information from the packets arriving at the receiver; and using said timing information at the receiver to align the time grid at the receiver with the time grid at the sender; and wherein said modulated signal is manifested as an offset in the rate of transmission of packets from the sender, said offset being an odd fraction ƒ
of a cycle of a clock signal such that the timing error at the receiver contains only high frequency components, and wherein the packet rate is offset by an amount equal to the ratio of the packet cycle and clock cycle multiplied by ƒ
. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method of recovering timing information in a packet network, wherein a modulated signal is used to transport additional information required for clock recovery between the sender and receiver across the network, wherein said modulated signal is manifested as an offset in the rate of transmission of packets from the sender, said offset being an odd fraction ƒ
- of a cycle of a clock signal such that the timing error at the receiver contains only high frequency components, and wherein the packet rate is offset by an amount equal to the ratio of the packet cycle and clock cycle multiplied by ƒ
. - View Dependent Claims (9, 10, 11)
- of a cycle of a clock signal such that the timing error at the receiver contains only high frequency components, and wherein the packet rate is offset by an amount equal to the ratio of the packet cycle and clock cycle multiplied by ƒ
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12. In a packet network linking a sender and receiver, an apparatus for recovering timing information across the network at the receiver comprising:
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a modulator at the sender for sending a modulated signal across the network conveying timing information; and a clock recovery unit at the receiver using said modulated signal to improve the accuracy of the recovered clock; and a control unit coupled to said modulator for varying the precise time of departure of outgoing packets to provide said modulated signal, said control unit varying the time of transmission of said packets to provide an offset in rate the transmission of said packets, wherein said offset is an odd fraction ƒ
of a cycle of a clock signal such that the timing error at the receiver contains only high frequency components; andwherein the packet rate is offset by an amount equal to the ratio of the packet cycle and clock cycle multiplied by ƒ
. - View Dependent Claims (13, 14, 15, 16, 17, 18)
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Specification