A packet-injection system for quantifying available service-level capacity of a network for projected network traffic, for new services or future services, said packet-injection system comprising: a network service-level manager, comprising: a computer; and a packet-injection manager implemented on said computer to control injected test packets in network traffic on said network; and a plurality of network switching devices, comprising: at least one network switching device, comprising at least one test-packet injector, wherein said test-packet injector is adapted to inject test packets into said network to simulate projected network traffic in response to a packet-injection command received from said packet-injection manager, said test packets being representative of the projected network traffic for new services or future services; at least one network switching device, comprising at least one test-packet collector, wherein said test-packet collector (120- 2) is adapted to remove an injected test packet from network traffic before reaching a client in response to a packet-removal command received from said packet-injection manager, and to provide data to said network service-level manager quantifying available service-level capacity associated with injection of said test packet to simulate said projected network traffic on said network; and characterised in that said test-packet injector is adapted to incrementally increase a rate of test packet transmission on said network until a desired service rate is achieved or exceeded to simulate increases in said projected network traffic, and in that the packet injection system further comprises at least one intermediate node adapted to monitor an effect of at least one injected test packet on available service-level capacity of said network and to report the status of available service-level capacity of the network back to the network service-level manager. a computer; and a packet-injection manager implemented on said computer to control injected test packets in network traffic on said network; and a plurality of network switching devices, comprising: at least one network switching device, comprising at least one test-packet injector, wherein said test-packet injector is adapted to inject test packets into said network to simulate projected network traffic in response to a packet-injection command received from said packet-injection manager, said test packets being representative of the projected network traffic for new services or future services; at least one network switching device, comprising at least one test-packet collector, wherein said test-packet collector (120- 2) is adapted to remove an injected test packet from network traffic before reaching a client in response to a packet-removal command received from said packet-injection manager, and to provide data to said network service-level manager quantifying available service-level capacity associated with injection of said test packet to simulate said projected network traffic on said network; and characterised in that said test-packet injector is adapted to incrementally increase a rate of test packet transmission on said network until a desired service rate is achieved or exceeded to simulate increases in said projected network traffic, and in that the packet injection system further comprises at least one intermediate node adapted to monitor an effect of at least one injected test packet on available service-level capacity of said network and to report the status of available service-level capacity of the network back to the network service-level manager. at least one network switching device, comprising at least one test-packet injector, wherein said test-packet injector is adapted to inject test packets into said network to simulate projected network traffic in response to a packet-injection command received from said packet-injection manager, said test packets being representative of the projected network traffic for new services or future services; at least one network switching device, comprising at least one test-packet collector, wherein said test-packet collector (120- 2) is adapted to remove an injected test packet from network traffic before reaching a client in response to a packet-removal command received from said packet-injection manager, and to provide data to said network service-level manager quantifying available service-level capacity associated with injection of said test packet to simulate said projected network traffic on said network; and characterised in that said test-packet injector is adapted to incrementally increase a rate of test packet transmission on said network until a desired service rate is achieved or exceeded to simulate increases in said projected network traffic, and in that the packet injection system further comprises at least one intermediate node adapted to monitor an effect of at least one injected test packet on available service-level capacity of said network and to report the status of available service-level capacity of the network back to the network service-level manager.