Interactions between TCP and ethernet flow control over Netgear XAVB2001 HomePlug AV links

HomePlug AV links are usually slower than the surrounding wired LAN links, creating a bottleneck where traffic may be buffered and delayed. To investigate the interactions between TCP congestion control and Ethernet flow control we trialled four TCP variants over a HomePlug AV link using two Netgear XAVB2001 devices. We observed that the XAVB2001's use of Ethernet flow control effectively concatenates the buffers in both the XAVB2001 and the directly attached sending host. This led to multi-second RTTs when using NewReno and CUBIC (loss-based) TCPs, which is significantly troublesome for multimedia traffic on home LANs. In contrast, Vegas and CDG (delay-based) TCPs kept buffer utilisation low, and induced five to ten milliseconds RTT. While keeping RTT low, CDG achieved similar goodput to NewReno and CUBIC. Vegas achieved roughly one third the goodput of the other three TCPs.