Communications - February 2009

practice

DoI: 10.1145/1461928.1461944

Given the Internet’s bottlenecks, how can we
build fast, scalable, content-delivery systems?
BY tom LeIGhton
Improving
Performance
on the Internet
When it coMeS
to achieving performance,
reliability, and scalability for commercial-grade Web
applications, where is the biggest bottleneck? In many
cases today, we see that the limiting bottleneck is the
middle mile, or the time data spends traveling back
and forth across the Internet, between origin server
and end user.
This wasn’t always the case. A decade ago, the last
mile was a likely culprit, with users constrained to
sluggish dial-up modem access speeds. But recent
high levels of global broadband penetration—more
than 300 million subscribers worldwide—have not
only made the last-mile bottleneck history, they have
also increased pressure on the rest of the Internet
infrastructure to keep pace.

5

Today, the first mile—that is, origin infrastructure— tends to get most of the attention when it comes to designing Web applications. This is the portion of the problem that falls most within an application

architect’s control. Achieving good first-mile performance and reliability is now a fairly well-understood and tractable problem. From the end user’s point of view, however, a robust first mile is necessary, but not sufficient, for achieving strong application performance and reliability.

This is where the middle mile comes in. Difficult to tame and often ignored, the Internet’s nebulous middle mile injects latency bottlenecks, throughput constraints, and reliability problems into the Web application performance equation. Indeed, the term middle mile is itself a misnomer in that it refers to a heterogeneous infrastructure that is owned by many competing entities and typically spans hundreds or thousands of miles.

This article highlights the most serious challenges the middle mile presents today and offers a look at the approaches to overcoming these challenges and improving performance on the Internet.