We propose to use optical correlation to measure the quality of an optical link in real time, staying completely within the optical domain. We transmit a test signal of 010 and correlate the received degrade signal with 010. The strength and shape of the output measure dispersion and attenuation compared with minutes by traditional methods. Correlation becomes feasible owing to the recent development of tapped delay lines with very large numbers of taps. We present simulations showing that this technique can detect attenuation, dispersion, noise, and jitter. With this instantaneous quality-of-service information available to all nodes in a network, new protocols will enable the network to select paths based on quality, allowing service providerto guarantee varying levels of service. We present one such protocol.