Method of providing synchronous transport of packets between asynchronous network nodes in a frame-based communications network
First Claim
1. A method of providing synchronous transport of packets between asynchronous network nodes, each asynchronous network node having a local clock and transmitting and receiving packets to and from the asynchronous network according to an asynchronous network media access protocol, comprising:
- designating as a master node an asynchronous network node capable of transmitting and receiving packets on the asynchronous network;
designating as a slave node each non-master asynchronous network node which desires to synchronously transport packets across the asynchronous network as a slave node;
synchronizing a master node clock of the master node with a slave node clock of each slave node;
determining at the master node, a best arrival time for the reception by the master node of each particular packet transmitted by each particular slave node;
communicating from the master node to the slave nodes best arrival times for packets transmitted from slave nodes to the master node;
determining at each slave node best packet assembly times for packets to be transmitted by the particular slave node to the master node in the future in order for the packets to be received by the master node at future master clock referenced best arrival times;
continuously correcting each slave node clock compared with the master node clock to smooth slave clock error to an average of zero compared with the master clock as a reference in response to a message from the master node;
preparing packets for transmission at slave nodes according to determined future best packet assembly time information; and
transmitting packets at slave nodes according to the determined future best packet assembly time information.
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Abstract
A method of providing synchronous transport of packets between asynchronous network nodes, each asynchronous network node having a local clock and transmitting and receiving packets to and from the asynchronous network according to an asynchronous network media access protocol. An asynchronous network node capable of transmitting and receiving packets on the asynchronous network is designated as a master node. Each non-master asynchronous network node which desires to synchronously transport packets across the asynchronous network as a slave node and each slave node is designated as a slave node. A master node clock of the master node is synchronized with a slave node clock of each slave node. A best arrival time for the reception by the master node of each particular packet transmitted by each particular slave node is determined at the master node. Best arrival times for packets transmitted from slave nodes to the master node are communicated from the master node to the slave nodes. Best packet assembly times for packets to be transmitted by the particular slave node to the master node in the future in order for the packets to be received by the master node at future master clock referenced best arrival times. Each slave node clock is continuously corrected compared with the master node clock to smooth slave clock error to an average of zero compared with the master clock as a reference in response to a message from the master node. Packets for transmission at slave nodes according to determined future best packet assembly time information. Packets at slave nodes are then transmitted according to the determined future best packet assembly time information.
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Citations
11 Claims
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1. A method of providing synchronous transport of packets between asynchronous network nodes, each asynchronous network node having a local clock and transmitting and receiving packets to and from the asynchronous network according to an asynchronous network media access protocol, comprising:
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designating as a master node an asynchronous network node capable of transmitting and receiving packets on the asynchronous network;
designating as a slave node each non-master asynchronous network node which desires to synchronously transport packets across the asynchronous network as a slave node;
synchronizing a master node clock of the master node with a slave node clock of each slave node;
determining at the master node, a best arrival time for the reception by the master node of each particular packet transmitted by each particular slave node;
communicating from the master node to the slave nodes best arrival times for packets transmitted from slave nodes to the master node;
determining at each slave node best packet assembly times for packets to be transmitted by the particular slave node to the master node in the future in order for the packets to be received by the master node at future master clock referenced best arrival times;
continuously correcting each slave node clock compared with the master node clock to smooth slave clock error to an average of zero compared with the master clock as a reference in response to a message from the master node;
preparing packets for transmission at slave nodes according to determined future best packet assembly time information; and
transmitting packets at slave nodes according to the determined future best packet assembly time information. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. In an asynchronous communications network having a master node and one or more slave nodes, a method of synchronizing a master node clock of the master node with a slave node clock of each slave node, comprising:
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sending timestamp report messages in pairs from the master node to slave nodes at periodic intervals by;
sending a first timestamp report message from the master node to the slave nodes;
recording master timestamp information at the master node at a defined time during transmission of the first timestamp report message of a pair corresponding to the transmission of the first timestamp report message of a pair; and
sending a second timestamp report message from the master node to the slave nodes which contains the master timestamp information; and
receiving timestamp report messages in pairs by the slave nodes from the master node by;
recording a slave timestamp at the slave nodes at a fixed time during reception of each timestamp report message to provide a recorded timestamp of the first timestamp report message at the slave nodes;
comparing the recorded timestamp of the first timestamp report message of each pair at the particular slave node with the master timestamp information from within the second timestamp report message of the same pair to determine a master clock offset from the slave clock of the slave nodes; and
adjusting the slave clock of the slave nodes to be synchronized with the master clock based on the master clock offset.
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Specification