Improving
Performance
on the Internet

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.

S TUCK IN THE MIDDLE

While we often refer to the Internet as a single entity, it is actually composed of 13,000 different competing networks, each providing access to some small subset of end users. Internet capacity has evolved over the years, shaped by market economics. Money flows into the networks from the first and last miles, as companies pay for hosting and end users pay for access. First- and last-mile capacity have grown 20- and 50-fold, respectively, over the past five to 10 years.

On the other hand, the Internet’s middle mile—made up of the peering and transit points where networks trade traffic—is literally a no man’s land. Here, economically, there is very little incentive to build out capacity. If anything, networks want to minimize traffic coming into their networks that they don’t get paid for. As a result, peering points are often overburdened, causing packet loss and service degradation.

The fragile economic model of peering can have even more serious consequences. In March 2008, for

example, two major network providers, Cogent and Telia, de-peered over a business dispute. For more than a week, customers from Cogent lost access to Telia and the networks connected to it, and vice versa, meaning that Cogent and Telia end users could not reach certain Web sites at all.

Other reliability issues plague the middle mile as well. Internet outages have causes as varied as transoceanic cable cuts, power outages, and DDoS (distributed denial of service) attacks. In February 2008, for example, communications were severely disrupted in Southeast Asia and the Middle East when a series of undersea cables were cut. According to TeleGeography, the cuts reduced bandwidth connectivity between Europe and the Middle East by 75 percent. ⁸

Internet protocols such as BGP (Border Gateway Protocol, the Internet’s primary internetwork routing algorithm) are just as susceptible as the physical network infrastructure. For example, in February 2008, when Pakistan tried to block access to You Tube from within the country by broadcasting a more specific BGP route, it accidentally caused a near-global You Tube blackout, underscoring the vulnerability of BGP to human error (as well as foul play). ²

The prevalence of these Internet reliability and peering-point problems means that the longer data must travel through the middle mile, the more it is subject to congestion, packet loss, and poor performance. These middle-mile problems are further exacerbated by current trends—most notably the increase in last-mile capacity and demand. Broadband adoption continues to rise, in terms of both penetration and speed, as ISPs invest in last-mile infrastructure. AT&T just spent approximately $6.5 billion to roll out its U-verse service, while Veri-zon is spending $23 billion to wire 18 million homes with FiOS (Fiber-optic Service) by 2010.^{7, 6} Comcast also recently announced it plans to offer speeds of up to 100 Mbps within a year. ³

Demand drives this last-mile boom: Pew Internet’s 2008 report shows that one-third of U.S. broadband users have chosen to pay more for faster connections. ⁴ Akamai Technologies’ data, shown in table 1, reveals that 59 percent of its global users have broadband connections (with speeds greater than 2 Mbps), and 19 percent of global users have “high broadband” connections greater than 5 Mbps—fast enough to support DVD-quality content. ² The high-broadband numbers represent a 19 percent increase in just three months.