A packet mapper prioritizes streams of data packets in a computer network, each data packet having a packet header containing feature values descriptive of the data packet. The packet mapper includes a mapping table that associates application-related features with network-reserved feature values from a range of feature values reserved for use by selected network data packet streams, and a feature value mapper that performs at least one of (i) in each packet header having an application-related feature value associated with a network-reserved feature value, substituting the associated network-reserved feature value for the application-related feature value, and (ii) in each packet header having a network-reserved feature value associated with an application-related feature value, substituting the associated application-related feature value for the network-reserved feature value.