Clock reconstruction for time division multiplexed traffic transported over asynchronous ethernet networks
First Claim
1. A method of clock synchronization for use in transporting synchronous traffic over an asynchronous network, said method comprising the steps of:
- extracting a network timestamp from packets transported over said asynchronous network;
generating a local timestamp for each received packet utilizing a local clock source;
fitting a best straight line through sample points of network timestamp data and local timestamp data and generating a clock control signal in accordance with the resulting slope of said line; and
adjusting said local clock source in accordance with said clock control signal so as to generate a reconstructed clock therefrom.
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Accused Products
Abstract
A clock reconstruction mechanism for synchronous TDM communications traffic transported over asynchronous networks such as Ethernet networks. The invention is applicable to edge switches in Metropolitan Area Networks (MANs) that transport legacy TDM traffic using a Circuit Emulation Services (CES) module whereby TDM traffic is encapsulated and transported across the Ethernet network where it is de-encapsulated and clocked out to the destination. The mechanism encapsulates the input TDM data stream into Ethernet packets and inserts a network timestamp within the packet. At the destination CES, a local timestamp is generated for each received packet as it is received. The network timestamp is extracted and input along with the local timestamp to a Digital Time Locked Loop (DTLL) which is operative to accurately reconstruct the original transmit TDM clock. The filter in the DTLL performs a Least Squares Regression (LSR) algorithm and Infinite Impulse Response (IIR) filter algorithm to generate a clock control signal for adjusting the clock generated.
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Citations
37 Claims
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1. A method of clock synchronization for use in transporting synchronous traffic over an asynchronous network, said method comprising the steps of:
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extracting a network timestamp from packets transported over said asynchronous network; generating a local timestamp for each received packet utilizing a local clock source; fitting a best straight line through sample points of network timestamp data and local timestamp data and generating a clock control signal in accordance with the resulting slope of said line; and adjusting said local clock source in accordance with said clock control signal so as to generate a reconstructed clock therefrom. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. An apparatus for reconstructing a clock for synchronous traffic transported over an asynchronous network, comprising:
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means for extracting a network timestamp from packets received over said asynchronous network, said network timestamp generated using a master clock and transported over said asynchronous network; means for generating a local timestamp for each received packet from utilizing a reconstructed clock generated by a local clock source; a filter to track differences between said local clock and a master clock used to generate said received network timestamp by fitting a best straight line through sample points of said network timestamp and said local timestamp and generating a clock control signal in accordance with the resulting slope of said line; and a clock generator comprising said local clock source and to output said reconstructed clock having a frequency determined in accordance with said clock control signal. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33)
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34. A Circuit Emulation Services (CES) apparatus for transmitting and receiving synchronous TDM traffic over an synchronous Ethernet network, comprising:
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a PHY circuit for receiving and transmitting Time Division Multiplexing (TDM) based communications; an encapsulation module comprising; means for segmenting received TDM frames into one or more Ethernet packets; means for generating and inserting a network timestamp in each Ethernet packet before transmission over said Ethernet network; means for receiving Ethernet packets from said Ethernet network, re-assembling TDM frames and extracting received network timestamps therefrom, said re-assembled TDM frames output utilizing a reconstructed TDM clock; a clock reconstruction module for generating said reconstructed TDM clock and comprising; means for generating a local timestamp for each received packet utilizing said reconstructed clock generated by a local clock source; a filter to track differences between said local clock and a master clock used to generate said received network timestamp by fitting a best straight line through sample points of said network timestamp and said local timestamp and generating a clock control signal in accordance with the resulting slope of said line; and a clock generator comprising said local clock source, said clock generator for outputting said reconstructed clock having a frequency determined in accordance with said clock control signal.
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35. An edge switch, comprising:
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a plurality of user ports for interfacing said edge switch to one or more users; a circuit Emulation Services (CES) module comprising; a PHY circuit adapted to receive and to transmit Time Division Multiplexing (TDM) based communications; an encapsulation module comprising means for segmenting received TDM frames into one or more Ethernet packets, means for generating and inserting a network timestamp in each Ethernet packet before transmission over said Ethernet network and means for receiving Ethernet packets from said Ethernet network, re-assembling TDM frames and extracting received network timestamps therefrom, said re-assembled TDM frames output utilizing a reconstructed TDM clock; a clock reconstruction module for generating said reconstructed TDM clock and comprising means for generating a local timestamp for each received packet utilizing said reconstructed clock generated by a local clock source, a filter for tracking differences between said local clock and a master clock used to generate said received network timestamp by fitting a best straight line through sample points of said network timestamp and said local timestamp and generating a clock control signal in accordance with the resulting slope of said line and a clock generator comprising said local clock source and operative to output said reconstructed clock having a frequency determined in accordance with said clock control signal; a plurality of network ports for interfacing said edge switch to one or more communication links; and a packet processor comprising ingress packet processing means and egress packet processing means.
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36. A method of clock synchronization for use in transporting synchronous traffic over an asynchronous network, said method comprising the steps of:
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extracting a network timestamp from packets transported over said asynchronous network; generating a local timestamp for each received packet utilizing a local clock source; applying an Infinite Impulse Response (IIR) filter to network timestamp data and local timestamp data to generate a clock adjustment signal; and adjusting said local clock source in accordance with said clock adjustment signal so as to generate a reconstructed clock therefrom.
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37. A network switch, comprising:
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a plurality of user ports for interfacing said edge switch to one or more users; a Circuit Emulation Services (CES) module comprising; a PHY circuit to receive and to transmit Time Division Multiplexing (TDM) based communications; an encapsulation module comprising means for segmenting received TDM frames into one or more Ethernet packets, means for generating and inserting a network timestamp in each Ethernet packet before transmission over said Ethernet network and means for receiving Ethernet packets from said Ethernet network, re-assembling TDM frames and extracting received network timestamps therefrom, said re-assembled TDM frames output utilizing a reconstructed TDM clock; a clock reconstruction module for generating said reconstructed TDM clock, said clock reconstruction module comprising; means for extracting a network timestamp from packets transported over said asynchronous network; means for generating a local timestamp for each received packet utilizing a local clock source; means for applying an Infinite Impulse Response (IIR) filter to network timestamp data and local timestamp data to generate a clock adjustment signal; means for adjusting said local clock source in accordance with said clock adjustment signal so as to generate a reconstructed clock therefrom; a plurality of network ports for interfacing said edge switch to one or more communication links; and a packet processor comprising ingress packet processing means and egress packet processing means.
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Specification