Buyers' Guide to Content Delivery Networks 2017

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Use caution in deciding in how many points of presence (POPs) or edge locations you choose to proactively store content in anticipation of audience groupings. Choosing to replicate content at various POPs is known as pushing content to these edge locations, and that can end up costing more than just allowing the CDN itself to optimize which locations house your content.

KeyCDN, for instance, offers free storage for pull zones but charges a monthly price for storage in push zones, ranging from 47 cents to 27 cents per GB per month.

Geography and Regions

For those interested in using a single CDN across multiple geographies and regions, pricing for both storage and bandwidth may vary by region.

Not every CDN is capable of delivering across multiple regions, but those that can often charge for interregional transport (e.g., the cost of moving content from one CDN storage POP to another POP). To visualize this concept, visit the CDN Calculator and try a number of different regions along with an aggregate monthly bandwidth amount.

Some CDNs will publicize their pricing per region, while others will hide the cost in blended pricing. For instance, Amazon CloudFront shows pricing from 8 cents per GB (Africa, Europe, and the U.S.) to 20 cents per GB (South America) with Asia falling in the mid-range of 14 cents per GB.

HTTP Requests

Every time an end-user application needs to retrieve data, it issues a request for the specific content, whether from a database or directly from a streaming server. For content that resides on a CDN, these requests may result in a charge as the CDN negotiates which edge location to deliver the requested content from.

With HTTP-based streaming technologies comprising thousands of requests—via a manifest file—for thousands of small files at varying resolutions, the number of requests can rise dramatically.

The good news is that few CDNs charge for buckets of requests, and even those CDNs only charge for buckets of 10,000 requests at a very nominal cost per bucket. The bad news is that HTTPS or SSL-based requests (which are required by some new streaming protocols such as WebRTC) will cost more than unsecure HTTP requests.

Interconnection: The Missing Link

At the beginning of this Buyers’ Guide, I mentioned that there are continuing innovations underway to help CDNs scale up to television-sized audiences, especially when it comes to live-linear OTT.

One of those innovations is being driven by the IETF, centering on interconnection between multiple CDNs. Even the largest CDN would have trouble delivering a TV-sized live streaming audience all by itself, so an IETF working group has been tasked with submitting specifications around CDNI.

While the CDNI working group isn’t looking to define new protocols for acquiring content across CDNs or even protocols and algorithms for intra-CDN operations, it is tasked with finding ways to deliver content to an end user across multiple CDNs.

“It is generally desirable that a given item of content can be delivered to an end user regardless of that end user’s location or attachment network,” the CDNI working group webpage notes, adding that this approach “creates a need for interconnecting (previously) standalone CDNs so they can interoperate and collectively behave as a single delivery infrastructure.”

Using existing IETF protocols for transport and message exchange, the CDNI working group has recently submitted specification for CDNI logging, control, request routing, and even metadata continuity.

What remains to be seen, though, is the cost of transit and storage between CDNs once these interconnection standards are ratified. We’ll keep an eye on this for our Streaming Media readers throughout 2017.

This article was published in the Spring 2017 European edition of Streaming Media magazine. 

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