Tracking transport-layer evolution with PATHspider

Abstract

The ossification of the Internet protocol stack, due in large part to mangling of packets by middleboxes, has led to a relatively slow rate of change in today's Internet. We have developed the PATHspider active Internet measurement tool which performs onesided measurements of a variety of transport-layer features and extensions, to investigate these impairments to protocol evolution along an Internet path. Data collected with PATHspider can be used both to determine the degree of support for these features, as well as to detect connectivity issues caused by attempting to use them. The wider aim of this effort is to provide quantifiable input to protocol design and deployment choices that can be based on the level of impairment present in the Internet.This paper details PATHspider's design, and applies it to trace the evolution of deployment of two extensions to TCP, Explicit Congestion Notification (ECN) and the newer TCP Fast Open (TFO); as well as the degree of interference with the Differentiated Services Code Point (DSCP) carried in the IP header. Our ECN results, in particular, expand on a long-term study beginning in 2012, and show continued linear adoption of ECN. Automating PATHspider measurements has allowed us to collect far more data than in previous campaigns, allowing us to better distinguish ECN-linked connectivity failures from transient effects. Interestingly, we observe a correlation between ECN-linked connectivity failure in the core of the network with the presence of large-scale, heterogeneous Internet censorship infrastructure.

Investigating the Delay Impact of the DiffServ Code Point (DSCP)

“…While the blackholing finding was not confirmed by other work, the rest of the results are more similar: in line with [2], the authors of [8], [9] (focusing on mobile edge networks) and [10] find that the DSCP field is often rewritten, and particularly often zeroed, by routers along a path. Setting the field to zero means that any possible effect from the input DSCP value further downstream is eliminated, but otherwise this is not getting in the way of "normal" communication.…”

Tracing Internet Path Transparency

“…PATHspider [4] is an active measurement tool that is designed to address exactly the question whether a certain path on the Internet is transparent to a given protocol or protocol feature under test. It has been developed and extended over the last couple of years and been used in a diverse set of measurements [5], [6].…”