Dissecting Apple's Meta-CDN during an iOS Update

TL;DR

This paper analyzes Apple's self-operated Meta-CDN during an iOS update, revealing its structure, request-mapping, cache locations, load-sharing behavior, and third-party traffic offloading effects on the network.

Contribution

It provides the first detailed measurement and analysis of Apple's Meta-CDN, including its infrastructure, behavior during a major update, and impact on third-party CDNs.

Findings

Apple's CDN uses multiple CDNs with specific cache locations.

During the iOS update, load sharing increased significantly.

Third-party CDNs experienced a 438% traffic increase during the event.

Abstract

Content delivery networks (CDN) contribute more than 50% of today's Internet traffic. Meta-CDNs, an evolution of centrally controlled CDNs, promise increased flexibility by multihoming content. So far, efforts to understand the characteristics of Meta-CDNs focus mainly on third-party Meta-CDN services. A common, but unexplored, use case for Meta-CDNs is to use the CDNs mapping infrastructure to form self-operated Meta-CDNs integrating third-party CDNs. These CDNs assist in the build-up phase of a CDN's infrastructure or mitigate capacity shortages by offloading traffic. This paper investigates the Apple CDN as a prominent example of self-operated Meta-CDNs. We describe the involved CDNs, the request-mapping mechanism, and show the cache locations of the Apple CDN using measurements of more than 800 RIPE Atlas probes worldwide. We further measure its load-sharing behavior by observing a major iOS update in Sep. 2017, a significant event potentially reaching up to an estimated 1 billion iOS devices. Furthermore, by analyzing data from a European Eyeball ISP, we quantify third-party traffic offloading effects and find third-party CDNs increase their traffic by 438% while saturating seemingly unrelated links.