It goes without saying that people enjoy using the Internet more when response times are fastest. But most of us are not as concerned about why websites respond more quickly, as long as they do. There are many factors that contribute to faster (and more satisfying) web experiences. Certainly, faster broadband connectivity and well-designed web sites play a role. And websites that leverage content delivery networks (CDNs), which distribute web content to servers located closer to end-users, outperform sites that don't.
But even CDNs stand to benefit from ongoing technical innovation, especially when accompanied by the promise of faster response times and higher quality of experience (QoE). Which leads us to the topic of end-user mapping. This week, a trio of researchers from Akamai Technologies and the University of Massachusetts, Amherst presented their paper "End-User Mapping: Next Generation Request Routing for Content Delivery" at the ACM SIGCOMM 2015 conference in London, UK.
Mapping is a core component of a CDN that uses the Internet's Domain Name System (DNS) protocol to route content requests from an end-user to a nearby CDN server that is best able to serve that content. Whereas CDN mapping has traditionally relied on the location of the recursive DNS server used by the end-user, end-user mapping leverages a recent extension to the DNS protocol called "EDNS0 Client Subnet" (ECS) that inserts the network portion of the end-user's IP address (typically the first three octets) into the DNS request. With this added information, content requests can be routed to a CDN server closest to the end-user's actual location rather than the location of the end-user's DNS server. In theory, the end-user should experience much faster response times as a result.
What's newsworthy about this isn't the ECS extension per se, which has actually been standardized for a couple of years. What's newsworthy is that the paper, written by Fangfei Chen, Ramesh Sitaraman and Marcelo Torres of Akamai, scientifically quantifies for the first time how ECS-enabled end-user mapping can speed up the Internet, potentially for hundreds of millions of end-users around the globe.
Using measurements taken from Akamai's production network, the paper demonstrates that end-user mapping provides significant performance benefits for clients who use public DNS resolvers, including an eight-fold decrease in mapping distance, a two-fold decrease in round trip time (RTT) and content download time and a 30% improvement in the time-to-first-byte for web site requests. Figures 1 and 2 below illustrate the performance gains.
Figure 1 - Average round-trip latency (RTT) before and after end-user mapping
Figure 1 above shows the average round-trip time (RTT), experienced by end-users in select countries that used public DNS resolvers. RTT measures latency from the end-user's browser to the CDN's content server and back. Average RTT decreased by nearly 50% when end-user mapping technology was rolled-out in April. Figure 2 below shows how, after the rollout of end-user mapping, the decrease in round trip latencies translated to a corresponding decrease in the time for end-users to download web page content. Note that the median time for downloading web page content decrease by 100+ milliseconds, a 50% decrease.
Figure 2 - Cumulative distribution function of the time for end-users to download web page content
In practice, end-user mapping is just beginning to catch on. In many cases, ISPs and DNS providers will have to upgrade their DNS infrastructure with servers that support the ECS capability (Akamai, Google and OpenDNS are examples of vendors that support ECS). Providers should especially look for implementations in which both the recursive resolver and authoritative name server support ECS. There are also possible scaling challenges associated with end-user mapping; the paper mentions that implementing it for public DNS resolvers resulted in a multi-fold increase in the number of DNS queries generated by those resolvers.
Still, the improvements provided through end-user mapping are an exciting development, both for ISPs looking to deliver (and possibly even monetize) better end-user QoE, and for end-users who are forever seeking the Internet Nirvana of instantaneous response.
Jonathan Zarkower is Senior Manager of Product Marketing for Carrier Products at Akamai.