PROTOCOL FOR CLOCK DISTRIBUTION AND LOOP RESOLUTION
In response to a network topology change, a clock root node calculates a new clock path for each affected node by building a clock source topology tree, and identifying from that tree a path to the network node from a clock source of higher or equal stratum relative to that network node. The root node then sends a network message to each node indicating the new path that the node should use. Each node receives the message and compares the new path with the existing path. If the paths are different then the node acquires the new path just received in the message. If the paths are the same then the node does nothing and discards the message.
1 . A network comprising a set of nodes, the set of nodes including a root node, the root node being aware of nodal adjacency and nodal clock quality level for the set of nodes and being configured to set up and maintain a network clock distribution infrastructure for the set of nodes by:
creating an eligibility matrix of elements that do not violate clock sourcing hierarchy constraints;
deriving a clock distribution tree topology indicative of clock sourcing for a plurality of nodes from the eligibility matrix;
detecting a network topology change;
identifying a node affected by the network topology change;
calculating, based at least in-part on the clock distribution tree topology, a new clock distribution path for the affected node; and
sending an indication of the new clock distribution path to the affected node; and
the affected node being configured:
to receive the indication of the new clock distribution path; and
to receive clock signal packets from other nodes of the network; and
to process clock signal packets based on the new clock distribution path.
2 . The network of claim 1 , wherein the root node is selected from among a plurality of candidate Primary Reference Clocks (PRCs).
3 . The network of claim 1 , wherein the root node is configured to calculate the new clock distribution path for the affected node by identifying, from the clock distribution tree topology, a path to the affected node from a clock source of higher or equal stratum relative to the affected node.
4 . The network of claim 1 , wherein the root node is configured to build a spanning tree with paths from the root node to leaf nodes with clock levels satisfying clock sourcing constraints.
5 . The network of claim 4 , wherein the nodes are configured to report indications of link availability and clock quality to the root node.
6 . The network of claim 5 , wherein the root node is configured to prompt communication, by neighboring nodes in the spanning tree, of the indications of link availability and clock quality.
7 . The network of claim 1 comprising a plurality of distinct sets of nodes, each distinct set of nodes including a respective root node, each respective root node being aware of nodal adjacency and nodal clock quality level for a respective distinct set of nodes and being configured to set up and maintain a network clock distribution infrastructure for the respective distinct set of nodes by:
creating a respective eligibility matrix of elements that do not violate clock sourcing hierarchy constraints;
deriving a respective clock distribution tree topology indicative of clock sourcing for a plurality of nodes from the respective eligibility matrix;
detecting a network topology change;
identifying a node in the respective distinct set of nodes which is affected by the network topology change;
calculating, based at least in-part on the respective clock distribution tree topology, a new clock distribution path for the affected node; and
sending an indication of the new clock distribution path to the affected node.
8 . The network of claim 7 , wherein the respective root node for each respective distinct set of nodes is selected from among a plurality of candidate Primary Reference Clocks (PRCs).
9 . The network of claim 7 , wherein each respective root node is configured to calculate the new clock distribution path for the affected node by identifying, from the respective clock distribution tree topology, a path to the affected node from a clock source of higher or equal stratum relative to the affected node.
10 . The network of claim 7 , wherein each respective root node is configured to build a respective spanning tree with paths from the respective root node to respective leaf nodes with clock levels satisfying clock sourcing constraints.
11 . The network of claim 10 , wherein the nodes of each distinct set are configured to report indications of link availability and clock quality to the respective root node of each distinct set.
12 . The network of claim 11 , wherein the respective root node is configured to prompt communication, by neighboring nodes in the respective spanning tree, of the indications of link availability and clock quality.
13 . The network of claim 1 , wherein the root node is configured to prompt the affected node:
to compare the new clock distribution path with a current clock distribution path; and
when the new clock distribution path differs from the current clock distribution path, to adopt the new path.
14 . The network of claim 13 , wherein the root node is configured to prompt reversion to the current clock distribution path following repair of fault resulting in the network topology change.
15 . The network of claim 1 , wherein the topology change comprises a link failure.
16 . The network of claim 1 , wherein the topology change comprises a node failure.
17 . The network of claim 1 , wherein the topology change comprises a link addition.
18 . The network of claim 1 , wherein the topology change comprises a node addition.
19 . The network of claim 1 , wherein the topology change comprises a clock quality degradation.
20 . The network of claim 1 , wherein the root node is configured to capture clock distribution topology.
21 . The network of claim 1 , wherein the root node is configured to capture failure conditions.
22 . The network of claim 1 , wherein the root node is configured to capture redundant clock source adjacency information.