iOS 9 download problems not due to overloaded delivery networks

Content delivery expert says plenty of capacity to handle iOS upgrade

The early download glitch users encountered in grabbing iOS 9 this week was not due to an overload on Apple's content delivery network (CDN), an expert said today.

"It was definitely not a capacity issue," said Dan Rayburn, an analyst with Frost & Sullivan who also writes on his own about CDN issues. "It was clearly a software or install issue."

Rayburn was referring to the first hour of iOS 9 availability on Wednesday, when users -- including several Computerworld staffers -- were unable to download the 1GB upgrade and were presented with a "Software Update Failed, An error occurred when downloading iOS 9" message.

Rayburn based his conclusion on data provided by and conversations with numerous ISPs (Internet service providers), and caching and CDN vendors. He declined to name those sources, with the exception of caching provider PeerApp, whom he cited in a blog post earlier Friday.

"It was business as usual," Rayburn said of the iOS 9 roll-out, which he noted was not the first time Apple has deployed a mobile operating system upgrade and dealt with the have-to-have-it-now eagerness of customers who want the newest version ASAP.

Newton, Mass.-based PeerApp, said Rayburn, saw traffic from spike at around 13Tbps (terabits-per-second) around 10 a.m. PT on Wednesday, when Apple released iOS 9. Nearly 80% of that traffic was being delivered though ProApp's caching network, preventing the 70 ISP and university clients' networks from being overloaded.

Rayburn said he did not have enough data to compare the total amount of traffic generated by the roll-out of iOS 9 with earlier upgrades. But he was adamant that none of the ISPs, caching providers or CDN vendors he spoke with had exceeded their capacity to deliver the new OS to users.

As it has before, Apple relied on its own CDN as well as third-party providers to get the bits to customers.

Several years ago, Apple began assembling its own CDN -- a network of data centers, including those it operates as well as servers at others' centers -- to have more control over the content it digitally ships over the Internet. Apple's CDN became operational in 2014, said Rayburn.

"Apple uses multiple data centers where they put their servers," Rayburn said, referring to both Cupertino's own as well as third-party data centers.

Along with the data centers, Apple has also rented capacity on a long-term basis from major ISPs and Internet transit providers so it can get its content, including OS upgrades, to users without the overloads that stymie downloads. The agreements, said Rayburn, let Apple expand and contract capacity as needed.

"In conversations I've had with some ISPs in the U.S., iOS 9 downloads have been accounting for anywhere between 8% and 15% of traffic inside their networks," Rayburn wrote on his blog today.

That range was within the usual for an iOS launch, although slightly more on the high end than in the past, Rayburn elaborated today in an interview.

One advantage Apple has over others in delivering large quantities of data to customers is that it regularly faces spikes like the iOS 9 roll-out, and thus has statistics it can review to forecast demand. "Apple knows their traffic patterns very well," said Rayburn, including peak demand times, the geographic distribution of its iOS device owners, and which ISPs are most used.

"There have been no capacity issues with iOS 9," said Rayburn. "I haven't heard a single problem [from ISPs and CDNs] about capacity."

As of noon PT, iOS 9's share of all iOS editions had reached 22.3%, virtually the same as iOS 8 at its 50-hour mark, according to data from analytics vendor Mixpanel. iOS 9 has almost doubled its share in the past 24 hours.


Copyright © 2015 IDG Communications, Inc.

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