Network clock synchronization scheme
First Claim
1. A method comprising establishing a clock distribution tree within a synchronous digital network through the use of spanning tree computations at n odes of the network, the computations relying, at least in part, upon the exchange of clock distribution messages between the nodes of the network, each clock distribution message including information regarding a clock source available at the source node of the message, said information indicating a priority level assigned to said clock source and a stratum level for said clock source.
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Abstract
A clock distribution tree for a digital network is automatically established through the use of spanning tree computations at nodes of the network. The computations rely, at least in part, upon the exchange of clock distribution messages between the nodes of the network. Each clock distribution message includes information regarding a clock source available at the source node of the message. The clock distribution tree is hierarchical in nature, with nodes that are lower in the hierarchy (i.e., at a higher stratum level) extracting clock from links with nodes that are higher in the hierarchy (i.e., at a lower stratum level); this helps preserve the synchronous digital hierarchy of the network. The spanning tree computations involve a root selection process and a convergence test. The root selection process is made on the basis of configuration vectors exchanged as part of the clock distribution messages. The configuration vectors include a port priority, a node stratum level and a primary reference source identifier. The convergence test includes determining whether a number of clock distribution messages received or transmitted equals a network maximum diameter parameter for the network.
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Citations
76 Claims
- 1. A method comprising establishing a clock distribution tree within a synchronous digital network through the use of spanning tree computations at n odes of the network, the computations relying, at least in part, upon the exchange of clock distribution messages between the nodes of the network, each clock distribution message including information regarding a clock source available at the source node of the message, said information indicating a priority level assigned to said clock source and a stratum level for said clock source.
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7. A method comprising automatically selecting at a node of a synchronous digital network a clocking source for the node according to a comparison of clock source configuration vectors, each vector associated with a port in the network and each vector identifying the associated port'"'"'s priority, a stratum level of a clock source available at that port and an indication of a primary reference clock source for that port, at least one of the vectors having been:
- a) sent to the node by another node of the synchronous digital network; and
, b) having been received by the node. - View Dependent Claims (8, 9, 10)
- a) sent to the node by another node of the synchronous digital network; and
- 11. A set of computer-readable instructions, which when executed by a processor of a network node cause the processor to help establish a clock distribution tree for a synchronous digital network to which the node belongs by executing spanning tree computations that rely, at least in part, upon the exchange of clock distribution messages between the node and other nodes of the synchronous digital network, each clock distribution message including information regarding a clock source available at the source node of the message, said information indicating a priority level assigned to said clock source and a stratum level for said clock source.
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17. A synchronous network node comprising a processor and readable media having executable instructions to automatically select a clocking source for the node according to a comparison of clock source configuration vectors, each vector associated with a port in a network and each vector identifying the associated port'"'"'s priority, a stratum level of a clock source available at that port and an indication of a primary reference clock source for that port, at least one of the vectors having been:
- a) sent to the node by another node of the synchronous digital network, and, b) having been received by the node.
- View Dependent Claims (18, 19, 20)
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21. A method to recognize a root clock source for a synchronous network, said method comprising:
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a) receiving, at a second node that is part of said synchronous network, a message that was sent from a first node, said first node also part of said synchronous network, said message comprising;
(i) an indication of a first priority level assigned to a first clocking signal, said first clocking signal recognized by said first node as said root clock source when said message was sent by said first node, said first clocking signal found at a first port within said network and (ii) an indication of a stratum level for said first clocking signal; and
,b) comparing, by said second node, said first priority level against a second priority level, said second priority level assigned to a second clocking signal, said second signal recognized by said second node as said root clock source. - View Dependent Claims (22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41)
receiving messages from adjacent nodes, each message indicating the stratum level of its respective adjacent node; and
, refusing to use, as said root port, a port of said second node where a link resides that communicates to those of said adjacent ports having a higher stratum level than said second node.
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- 42. A set of computer-readable instructions which, when executed by a processor of a second node that is part of a synchronous network, cause said processor to perform a method that identifies a root clock source for said synchronous network, said method comprising comparing a first priority level against a second priority level, said first priority level assigned to a first clocking signal, said first clocking signal found at a first port within said network, said first node having sent a message to said second node that included an indication o f said first priority level and an indication of a stratum level for said first clocking signal, said first node having recognized said first clocking signal as said root clock source when said message was sent, said second priority level assigned to a second clocking signal, said second clocking signal recognized by said second node as said root clock source.
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62. A second node, said second node capable of being part of a synchronous network, said second node comprising:
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a) means for receiving a message that was sent from a first node, said first node also part of said synchronous network, said message comprising;
(i) an indication of a first priority level for a first clocking signal, said first clocking signal recognized by said first node as a root clock source for said network when said message was sent, said first clocking signal found at a first port within said network and (ii) an indication of a stratum level for said first clocking signal; and
,b) means for comparing said first priority level against a second priority level, said second priority level for a second clocking signal, said second clocking signal recognized by said second node as said root clock source. - View Dependent Claims (63, 64, 65, 66, 67, 68, 69)
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70. An apparatus that can be used to implement a node within a synchronous digital network, said apparatus comprising a network clock distribution protocol entity, said network clock distribution protocol entity to identify a root clock source of said network, said network clock distribution protocol entity to send messages that contain:
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(i) an indication of a priority level of a clocking source that is recognized by said network clock distribution protocol entity as said root clock source; and
,(ii) an indication of a stratum level of said clocking source. - View Dependent Claims (71, 72, 73, 74, 75, 76)
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Specification