A method for communicating data descriptive of failure or degradation, the method comprising: in a network comprising a plurality of network nodes (40, 50, 60, 70) each configured to apply one or more service functions (42, 52, 62, 72) to traffic that passes the respective network nodes (40, 50, 60, 70) in a service path, receiving at a particular network node among the respective nodes of the service path an indication of a failure or degradation of a service function or application applied to traffic at the particular network node; generating at the particular network node data descriptive of the failure or degradation; determining at the particular network node a previous service hop network node; and communicating the data descriptive of the failure or degradation from the particular network node to the previous service hop network node; characterized in that determining the previous service hop network node comprises examining a context header, wherein a network service header comprises the context header and a service header, wherein the network service header is encapsulated by a transport header and wherein packets of the traffic for the service path are encapsulated by the network service header and wherein the context header is allocated to contain previous service hop location information and wherein the context header is populated by each of the respective network nodes along the service path so that the context header contains information identifying the location of the previous service hop network node at any point along the service path and wherein the context header is used to identify which of the service functions was applied at the previous service hop. in a network comprising a plurality of network nodes (40, 50, 60, 70) each configured to apply one or more service functions (42, 52, 62, 72) to traffic that passes the respective network nodes (40, 50, 60, 70) in a service path, receiving at a particular network node among the respective nodes of the service path an indication of a failure or degradation of a service function or application applied to traffic at the particular network node; generating at the particular network node data descriptive of the failure or degradation; determining at the particular network node a previous service hop network node; and communicating the data descriptive of the failure or degradation from the particular network node to the previous service hop network node; characterized in that determining the previous service hop network node comprises examining a context header, wherein a network service header comprises the context header and a service header, wherein the network service header is encapsulated by a transport header and wherein packets of the traffic for the service path are encapsulated by the network service header and wherein the context header is allocated to contain previous service hop location information and wherein the context header is populated by each of the respective network nodes along the service path so that the context header contains information identifying the location of the previous service hop network node at any point along the service path and wherein the context header is used to identify which of the service functions was applied at the previous service hop.