Exploring DSCP modification pathologies in the Internet

The differentiated service architecture (DiffServ) provides a means for network devices to classify traffic based on the DiffServ codepoint (DSCP) and to map the traffic to a specific QoS forwarding treatment. Successful use beyond the local network depends on consistent remarking and forwarding of the DSCP value inside and at the boundaries of DiffServ domains. This paper provides the results of a new widescale measurement campaign to examine how the DSCP value is altered as packets travel along a set of Internet paths. This allows us to infer whether a packet is likely to receive an appropriate QoS treatment and to comment the opportunities for more widely deploying DiffServ QoS. Our results identify a set of remarking pathologies, revealing that many deployed routers continue to use the previous semantics of the deprecated Type of Service (ToS) field. We also note that is not common to observe clearing of the bits in the DiffServ field, as previously believed for routers in the core of the Internet, although this varies significantly depending on the type of network studied. Our results are related to recent IETF work that recommends use of specific DSCP values.