SideStep and DraFTP

In Brief

Many studies have shown that the default Internet path can be suboptimal, leading to poor throughput between hosts. SideStep was the first scalable and efficient system to provide free, open access to alternative paths — sometimes doubling or tripling performance. It reused information from content delivery networks to locate quality overlay paths and stream data over them, and was packaged as a Java library and stream API easy to drop into an existing application.

To demonstrate the effect in something people actually used, we released DraFTP, an open-source FTP suite built on SideStep.

Motivation and Approach

The Detour study showed Internet paths are generally suboptimal in both latency and loss. RON — the Reliable Overlay Network project — then showed that diverting a transfer through an intermediate host often beats the direct path. Part of the reason is that ISPs carry each other’s traffic under business arrangements, and those arrangements outrank optimal path selection; a neighbouring ISP may simply have a better route than yours.

RON was never widely deployed because it required active probing with overhead proportional to the square of the number of nodes — unacceptable for Internet-scale applications with millions of users. The opposite approach, picking detour points at random, has negligible overhead and rarely helps.

SideStep sat between those extremes: it found high-quality detour points with high probability at a constant amount of measurement overhead per node. It did so by treating CDN redirection dynamics as hints about good candidates. Drafting Behind Akamai had already shown those redirections are driven primarily by network conditions; SideStep showed they are cheap to obtain, cheap to validate, and accurate enough to drive a large-scale detouring service.

In a measurement study across hundreds of computers worldwide, SideStep improved performance more than half the time. The rest of the time there was no better path to find, so performance was unchanged — it could not make throughput worse, because candidate paths were evaluated by splitting the stream across the current and candidate route.

Why the Names

We called it SideStep because it sidesteps the poor default path. The FTP suite is DraFTP because, like SideStep, it exploits drafting: letting CDNs absorb the cost of measurement, much as cyclists in a peloton travel fast by letting the riders in front break the wind.

On Using Someone Else’s Measurements

A recurring question was whether CDNs would try to stop this. They could try, but it seemed unlikely. Akamai already published measurement information publicly. SideStep used ordinary DNS lookups to gather hints and downloaded no content, and those lookups could be as infrequent as once an hour — a negligible load beside the hundreds of millions of people fetching CDN content daily. The requests were also indistinguishable from those of any normal user of that content, making them impractical to filter.

For the avoidance of doubt: this was not AkaRouting, Akamai’s paid detouring service. SideStep was free and used none of its paths.

Availability

SideStep was distributed as a background service with a stream API, alongside DraFTP, to users who registered on the lab site. It is no longer available.

Papers

• On the Effectiveness of Measurement Reuse for Performance-Based Detouring — INFOCOM 2009
• Drafting Behind Akamai (Travelocity-Based Detouring) — SIGCOMM 2006

People

Lead & PI

• Fabián E. Bustamante (Northwestern University)

Students

• David R. Choffnes
• Ao-Jan Su

Collaborators

• Aleksandar Kuzmanovic (Northwestern University)

Related Links

• Reusing CDN Measurements — the project SideStep was built for