Internet Connection Splitting: What’s Old is New Again

In the 1990s, many networks deployed performance-enhancing proxies (PEPs) that transparently split TCP connections to aid performance, especially over lossy, long-delay paths. Two recent developments have cast doubts on their relevance: the BBR congestion-control algorithm, which de-emphasizes loss as a congestion signal, and the QUIC transport protocol, which prevents transparent connection-splitting yet empirically matches or exceeds TCP's performance in wide deployment, using the same congestion control.

In light of this, are PEPs obsolete? This paper presents a range of emulation measurements indicating: "probably not." While BBR's original 2016 version didn't benefit markedly from connection-splitting, more recent versions of BBR do and, in some cases, even more so than earlier "loss-based" congestion-control algorithms. We also find that QUIC implementations of the "same" congestion-control algorithms vary dramatically and further differ from those of Linux TCP–-frustrating head-to-head comparisons. Notwithstanding their controversial nature, our results suggest that PEPs remain relevant to Internet performance for the foreseeable future.