A method, in data processing system having a control plane processor and one or more data plane processors, comprising: processing, in a data plane processor of the data processing system, an instruction requiring external assistance by a function or service that is not available in the data plane processor but is available on the control plane processor; in response to the step of processing, generating, in the data plane processor, a parameter area in a local store associated with the data plane processor; in response to the step of generating the parameter area, copying, in the data plane processor, input parameter data from one or more data registers of the data plane processor to the parameter area; in response to the step of copying, generating, in the data plane processor, an assisted call message (232, 350) for requesting assistance from the control plane processor; in response to the step of generating the assisted call message, inserting, in the data plane processor, a stop-and-signal instruction in an execution stack associated with the data plane processor, the stop-and-signal instruction based on the assisted call message; in response to the step of inserting, executing, in the data plane processor, the stop-and-signal instruction, wherein the stop-and-signal instruction causes execution of instructions by the data plane processor to stop and initiates the signaling of the control plane processor to process the assisted call message; in response to the step of executing, signaling, in the data plane processor, the control plane processor to process the assisted call message; and characterised by: in response to the step of signaling, receiving, in the data plane processor, into the parameter area one or more return values from the control plane processor, wherein the one or more return values are generated based on the control plane processor executing the function or service based on the assisted call message. processing, in a data plane processor of the data processing system, an instruction requiring external assistance by a function or service that is not available in the data plane processor but is available on the control plane processor; in response to the step of processing, generating, in the data plane processor, a parameter area in a local store associated with the data plane processor; in response to the step of generating the parameter area, copying, in the data plane processor, input parameter data from one or more data registers of the data plane processor to the parameter area; in response to the step of copying, generating, in the data plane processor, an assisted call message (232, 350) for requesting assistance from the control plane processor; in response to the step of generating the assisted call message, inserting, in the data plane processor, a stop-and-signal instruction in an execution stack associated with the data plane processor, the stop-and-signal instruction based on the assisted call message; in response to the step of inserting, executing, in the data plane processor, the stop-and-signal instruction, wherein the stop-and-signal instruction causes execution of instructions by the data plane processor to stop and initiates the signaling of the control plane processor to process the assisted call message; in response to the step of executing, signaling, in the data plane processor, the control plane processor to process the assisted call message; and characterised by: in response to the step of signaling, receiving, in the data plane processor, into the parameter area one or more return values from the control plane processor, wherein the one or more return values are generated based on the control plane processor executing the function or service based on the assisted call message. in response to the step of signaling, receiving, in the data plane processor, into the parameter area one or more return values from the control plane processor, wherein the one or more return values are generated based on the control plane processor executing the function or service based on the assisted call message.