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Data networks and nodes making up parts of data networks are arranged to derive information relating to the characterization of paths taken by data travelling between nodes in the networks. Path characterization information is fed back from a receiver of data to a provider of data, and informs nodes

Data networks and nodes making up parts of data networks are arranged to derive information relating to the characterization of paths taken by data travelling between nodes in the networks. Path characterization information is fed back from a receiver of data to a provider of data, and informs nodes subsequently forwarding data of characteristics of the downstream path. Also described are routing and related controlling nodes and methods for using such path characterization information to make informed routing and other decisions when forwarding data in a data network.

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1. A data network comprising: a provider node, a receiver node, and a plurality of intermediate nodes,the provider node being arranged to provide data to at least one of said intermediate nodes or to the receiver node,said intermediate nodes being arranged to receive data and forward data to at leas

1. A data network comprising: a provider node, a receiver node, and a plurality of intermediate nodes,the provider node being arranged to provide data to at least one of said intermediate nodes or to the receiver node,said intermediate nodes being arranged to receive data and forward data to at least one other intermediate node or to the receiver node, andthe receiver node being arranged to receive data from at least one intermediate node or from the provider node;wherein:said data comprises at least a part which relates to a dynamic path characterization metric, a condition of which is updatable as data of which it forms a part is passed from node to node, such that said condition is indicative of a state of a dynamic path characteristic which is changeable as the data traverses a path from the provider node to the receiver node, the condition of the dynamic path characterization metric indicating the state of the dynamic path characteristic;said provider node is arranged to assign an initial condition to the dynamic path characterization metric in respect of data provided by it according to a predetermined algorithm;said intermediate nodes are arranged to update the condition of the dynamic path characterization metric in respect of data they forward according to a predetermined algorithm;said receiver node is arranged to make available for the provider node discrepancy information indicative of a measure of any discrepancy between the condition of the dynamic path characterization metric in respect of data received by it and a predetermined target condition for the dynamic path characterization metric; andsaid provider node is arranged to assign a different initial condition to the dynamic path characterization metric in respect of subsequent data provided by it according to a predetermined algorithm that is dependent on discrepancy information received from said receiver node when the provider node receives discrepancy information from said receiver node, such that the different initial condition assigned in respect of said subsequent data differs from the initial condition assigned in respect of previous data provided by said provider node by a difference dependent on said discrepancy information. 2. A data network according to claim 1, wherein the condition of the dynamic path characterization metric at a node is indicative of a measure of congestion expected to be experienced by data on a path downstream of that node. 3. A data network according to claim 1, wherein the condition assigned to the dynamic path characterization metric is a value, and the predetermined target condition is a value. 4. A data network according to claim 1, wherein when said provider node assigns a different initial condition to the dynamic path characterization metric in respect of subsequent data provided by it, said different initial condition is assigned to decrease a corresponding discrepancy in respect of said subsequent data received by said receiver node. 5. A data network according to claim 4, wherein said different initial condition is assigned to maximize a possibility that said corresponding discrepancy in respect of said subsequent data received by said receiver node will be zero. 6. A data network according to claim 1, wherein an intermediate node is arranged to update the condition of the dynamic path characterization metric in response to a dynamic path characteristic associated with that node. 7. A data network according to claim 6, wherein said dynamic path characteristic relates to a measure of congestion on a path associated with that node. 8. A data network according to claim 6 wherein said dynamic path characteristic relates to a measure of congestion on a path downstream of that node. 9. A method for assigning dynamic path characterization metrics to data in a data network comprising a provider node, a receiver node, and a plurality of intermediate nodes, the provider node being arranged to provide data to at least one of said intermediate nodes or to the receiver node, said data comprising at least a part which relates to a dynamic path characterization metric, a condition of which is updatable as data of which it forms a part is passed from node to node, such that said condition is indicative of a state of a dynamic path characteristic which is changeable as the data traverses a path from the provider node to the receiver node, the condition of the dynamic path characterization metric indicating the state of the dynamic path characteristic, said intermediate nodes being arranged to receive data and forward data to at least one other intermediate node or to the receiver node, and the receiver node being arranged to receive data from at least one intermediate node or from the provider node; the method comprising: assigning an initial condition to the dynamic path characterization metric in respect of data provided by the provider node according to a predetermined algorithm;updating the condition of the dynamic path characterization metric in respect of data forwarded by said intermediate nodes according to a predetermined algorithm;monitoring a final condition of the dynamic path characterization metric in respect of data received by the receiver node, and determining discrepancy information indicative of a measure of any discrepancy between said final condition and a predetermined target condition for the dynamic path characterization metric; andassigning a different initial condition to the dynamic path characterization metric in respect of subsequent data provided by the provider node according to a predetermined algorithm that is dependent on said determined discrepancy information when said discrepancy information indicates such a discrepancy in respect of previous data provided by the provider node, such that the different initial condition assigned in respect of said subsequent data differs from the initial condition assigned in respect of said previous data by a difference dependent on said discrepancy information. 10. A method according to claim 9, wherein the condition assigned to the dynamic path characterization metric is a value, and the predetermined target condition is a value. 11. A feedback node for enabling an initial condition to be assigned to a dynamic path characterization metric in respect of data to be forwarded through a data network, said data network comprising a provider node, a receiver node and a plurality of intermediate nodes, said data comprising at least a part which relates to a dynamic path characterization metric, a condition of which is updatable as data of which it forms a part is passed from node to node, such that said condition is indicative of a state of a dynamic path characteristic which is changeable as the data traverses a path from the provider node to the receiver node, the condition of the dynamic path characterization metric indicating the state of the dynamic path characteristic; said provider node being arranged to assign an initial condition to the dynamic path characterization metric in respect of data according to a predetermined algorithm, and to provide said data to at least one of said intermediate nodes or to the receiver node; said intermediate nodes being arranged to receive data from said provider node or from one or more other intermediate nodes, to update a condition of the dynamic path characterization metric in respect of data received by them according to a predetermined algorithm, and to forward data to at least one other intermediate node or to the receiver node; and said receiver node being arranged to receive data from at least one intermediate node or from the provider node, and to make available for the feedback node information relating to the dynamic path characterization metric in respect of data received by it, said feedback node comprising: at least one message processor arranged to enable a different initial condition to be assigned to the dynamic path characterization metric in respect of subsequent data provided by the provider node according to a predetermined algorithm that is dependent on received discrepancy information when said feedback node receives information indicative of a discrepancy between a predetermined target condition for the dynamic path characterization metric and the condition of the dynamic path characterization metric in respect of previous data received by said receiver node, such that the different initial condition assigned in respect of said subsequent data differs from the initial condition assigned in respect of previous data provided by said provider node by a difference dependent on said discrepancy information. 12. A feedback node according to claim 11, wherein the condition assigned to the dynamic path characterization metric is a value, and the predetermined target condition is a value. 13. A feedback node according to claim 11, wherein when a different initial condition is assigned to the dynamic path characterization metric in respect of subsequent data, said different initial condition is assigned to decrease a corresponding discrepancy in respect of said subsequent data received by said receiver node. 14. A feedback node according to claim 11, said feedback node also serving as said provider node in said network. 15. A feedback node according to claim 14, said feedback node being arranged to assign a different initial condition to the dynamic path characterization metric in respect of subsequent data when it receives, from said receiver node, a measure of a discrepancy between said predetermined target condition for the dynamic path characterization metric and the condition of the dynamic path characterization metric in respect of previous data received by said receiver node. 16. A feedback node according to claim 14, said feedback node being arranged to assign a different initial condition to the dynamic path characterization metric in respect of subsequent data when it receives, from said receiver node, information indicative of the condition of the dynamic path characterization metric in respect of previous data received by said receiver node, and determines that there is a discrepancy between said condition of the dynamic path characterization metric and said predetermined target condition for the dynamic path characterization metric. 17. A feedback node according to claim 11, said feedback node also serving as said receiver node in said network. 18. A feedback node according to claim 17, said feedback node being arranged to make available for the provider node a measure of a discrepancy between said predetermined target condition for the dynamic path characterization metric and the condition of the dynamic path characterization metric in respect of previous data received by said receiver node, whereby to enable said provider node to assign a different initial condition to the dynamic path characterization metric in respect of subsequent data. 19. A feedback node according to claim 17, said feedback node being arranged to make available for the provider node information indicative of the condition of the dynamic path characterization metric in respect of previous data received by said receiver node, whereby to enable said provider node to assign a different initial condition to the dynamic path characterization metric in respect of subsequent data when said provider node determines that there is a discrepancy between said condition of the dynamic path characterization metric and said predetermined target condition for the dynamic path characterization metric. 20. A method of providing data in a data network comprising a provider node, a receiver node and a plurality of intermediate nodes, the provider node being arranged to provide data to at least one of said intermediate nodes or to the receiver node, said data comprising at least a part which relates to a dynamic path characterization metric, a condition of which is updatable as data of which it forms a part is passed from node to node, such that said condition is indicative of a state of a dynamic path characteristic which is changeable as the data traverses a path from the provider node to the receiver node, the condition of the dynamic path characterization metric indicating the state of the dynamic path characteristic; said intermediate nodes being arranged to receive data from said provider node or from one or more other intermediate nodes, to update a condition of the dynamic path characterization metric in respect of data received by them according to a predetermined algorithm, and to forward data to at least one other intermediate node or to the receiver node; and said receiver node being arranged to receive data from at least one intermediate node or from the provider node, and to make available for the provider node information indicative of a discrepancy between an eventual condition of the dynamic path characterization metric in respect of data received by it and a predetermined target condition for the dynamic path characterization metric; the method comprising: assigning an initial condition to the dynamic path characterization metric in respect of data according to a predetermined algorithm;providing said data to at least one of said intermediate nodes;receiving information relating to said eventual condition of the dynamic path characterization metric in respect of previously-provided data received by said receiver node; andassigning a different initial condition to the dynamic path characterization metric in respect of subsequent data according to a predetermined algorithm that is dependent on received discrepancy information when receipt of discrepancy information indicative of a measure of any discrepancy between said eventual condition of the dynamic path characterization metric and a predetermined target condition for the dynamic path characterization metric, such that the different initial condition assigned in respect of said subsequent data differs from the initial condition assigned in respect of previous data provided by said provider node by a difference dependent on said discrepancy information. 21. A method according to claim 20, wherein the condition assigned to the dynamic path characterization metric is a value, and the predetermined target condition is a value. 22. A method according to claim 20, said receiver node being arranged to make available for the provider node a measure of a discrepancy between said predetermined target condition for the dynamic path characterization metric and said eventual condition of the dynamic path characterization metric in respect of previous data received, whereby to enable said provider node to assign a different initial condition to the dynamic path characterization metric in respect of subsequent data. 23. A method according to claim 20, said receiver node being arranged to make available for the provider node information indicative of the condition of said dynamic path characterization metric in respect of previously received data, whereby to enable said provider node to assign a different initial condition to the dynamic path characterization metric in respect of subsequent data when said provider node determines that there is a discrepancy between said condition of the dynamic path characterization metric and said predetermined target condition for the dynamic path characterization metric. 24. A method for providing dynamic path characterization information for nodes in a network, said network comprising a plurality of nodes including a provider node, a receiver node, and at least one intermediate node, the provider node being arranged to provide data to at least one intermediate node or to the receiver node, an intermediate node being arranged to receive data and to forward data to at least one other intermediate node or to the receiver node, and the receiver node being arranged to receive data from the provider node or from at least one intermediate node, the method comprising: assigning an initial condition to a dynamic path characterization metric, condition of which is updatable as data of which it forms a part is passed from node to node, such that said condition is indicative of a state of a dynamic path characteristic which is changeable as the data traverses a path from the provider node to the receiver node, the condition of the dynamic path characterization metric indicating the state of the dynamic path characteristic, in respect of data provided by said provider node according to a predetermined algorithm, said dynamic path characterization metric being associated with said data and being subject to change as data is passed from node to node;updating the condition of the dynamic path characterization metric when an intermediate node receives said data;determining an eventual condition of the dynamic path characterization metric when said receiver node receives said data; andestablishing discrepancy information indicative of a measure of any discrepancy which exists between the eventual condition of the dynamic path characterization metric and a predetermined target condition;wherein, when it is established that a discrepancy does exist between said eventual condition and said predetermined target condition, said method further comprises:assigning a different initial condition to the dynamic path characterization metric in respect of subsequent data provided by said provider node according to a predetermined algorithm, such that the different initial condition assigned to the dynamic path characterization metric in respect of said subsequent data differs from the initial condition assigned to the dynamic path characterization metric in respect of said data provided by said provider node by a difference dependent on said discrepancy information;updating the condition of the dynamic path characterization metric in respect of said subsequent data according to a predetermined algorithm when an intermediate node receives said subsequent data; andmaking information indicative of the updated dynamic path characterization metric in respect of said subsequent data available to said intermediate node. 25. A method according to claim 24, wherein the condition assigned to the dynamic path characterization metric is a value, and the predetermined target condition is a value. 26. A method for providing dynamic path characterization information for nodes in a network, said network comprising a plurality of nodes including a provider node, a receiver node, and at least one intermediate node, the provider node being arranged to provide data to at least one intermediate node or to the receiver node, an intermediate node being arranged to receive data and to forward data to at least one other intermediate node or to the receiver node, and the receiver node being arranged to receive data from the provider node or from at least one intermediate node; the method comprising: assigning an initial condition to a dynamic path characterization metric, a condition of which is updatable as data of which it forms a part is passed from node to node, such that said condition is indicative of a state of a dynamic path characteristic which is changeable as the data traverses a path from the provider node to the receiver node, the condition of the dynamic path characterization metric indicating the state of the dynamic path characteristic, in respect of data provided by said provider node according to a predetermined algorithm, said dynamic path characterization metric being associated with said data and being subject to change as data is passed from node to node;updating the condition of the dynamic path characterization metric according to a predetermined algorithm when an intermediate node receives said data;determining an eventual condition of the dynamic path characterization metric when said receiver node receives said data; andestablishing discrepancy information indicative of a measure of any discrepancy which exists between the eventual condition of the dynamic path characterization metric and a predetermined target condition;wherein, when it is established that a discrepancy does exist between said eventual condition and said predetermined target condition, said method further comprises:assigning an initial condition to the dynamic path characterization metric in respect of subsequent data provided by said provider node according to a predetermined algorithm;updating the condition of the dynamic path characterization metric in respect of said subsequent data according to a predetermined algorithm when an intermediate node receives said subsequent data;making information indicative of the updated dynamic path characterization metric in respect of said subsequent data available to said intermediate node; andmaking information relating to the discrepancy between the eventual condition of the dynamic path characterization metric in respect of said data provided by said provider node and said predetermined target condition available to said intermediate node. 27. A method according to claim 26, wherein the condition assigned to the dynamic path characterization metric is a value, and the predetermined target condition is a value. 28. A path characterization system for providing dynamic path characterization information in association with a data network, said data network comprising a plurality of nodes including a provider node, a receiver node, and at least one intermediate node, the provider node being arranged to provide data to at least one intermediate node or to the receiver node, an intermediate node being arranged to receive data and to forward data to at least one other intermediate node or to the receiver node, and the receiver node being arranged to receive data from the provider node or from at least one intermediate node; the dynamic path characterization system comprising: a dynamic path characterization metric condition assigning means, associated with the provider node, arranged to assign an initial condition to a dynamic path characterization metric, a condition of which is updatable as data of which it forms a part is passed from node to node, such that said condition is indicative of a state of a dynamic path characteristic which is changeable as the data traverses a path from the provider node to the receiver node, the condition of the dynamic path characterization metric indicating the state of the dynamic path characteristic, in respect of data provided by said provider node according to a predetermined algorithm;a dynamic path characterization metric updating means, associated with an intermediate node, arranged to update the condition of the dynamic path characterization metric according to a predetermined algorithm when said node receives data; anda dynamic path characterization metric feedback means, associated with the receiver node, arranged to determine an eventual condition of the dynamic path characterization metric when said receiver node receives said data, and to make available for the dynamic path characterization metric condition assigning means discrepancy information indicative of a measure of any discrepancy between the eventual condition of the dynamic path characterization metric and a predetermined target condition for the dynamic path characterization metric; wherein said dynamic path characterization metric condition assigning means is arranged to assign a different initial condition to the dynamic path characterization metric in respect of subsequent data provided by said provider node according to a predetermined algorithm that is dependent on feedback indicative of a discrepancy when feedback is made available indicative of such a discrepancy between the eventual condition of the dynamic path characterization metric in respect of said data previously provided by said provider node and the predetermined target condition, such that the different initial condition assigned to the dynamic path characterization metric in respect of said subsequent data differs from the initial condition assigned to the dynamic path characterization metric in respect of data previously provided by said provider node by a difference dependent on said discrepancy information. 29. A dynamic path characterization system according to claim 28, wherein the condition assigned to the dynamic path characterization metric is a value, and the predetermined target condition is a value.