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Buyer's Guide: Content Delivery Networks

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This article appears in the February/March issue of Streaming Media magazine, the annual Streaming Media Industry Sourcebook. In these Buyer's Guide articles, we don't claim to cover every product or vendor in a particular category, but rather provide our readers with the information they need to make smart purchasing decisions, sometimes using specific vendors or products as exemplars of those features and services.

Over the past year, as pricing in the sector has reached a commoditized level, the definition of a content delivery network (CDN) has started to change. As pricing competition has narrowed their differentiation, CDNs have started to focus on the value-added parts of their propositions. If you call Akamai Technologies or Limelight Networks a CDN, company reps will do their best to point out that distribution is only a part of their services.

This means that while we can track pricing to some extent, as Dan Rayburn famously does at www.cdnpricing.com, it is becoming difficult to simply buy data transfer services from CDNs. These companies like to offer a richer range of services than pure byte-shifting. Each CDN now has its own online video platform (OVP), which provides content management and user interfaces. Each offers some form of relationship with advertising partners, and so on and so forth.

Still, there is a fairly clear set of key performance indicators (KPIs) for anyone who wants to engage the services of these companies. These are outlined in the accompanying chart.

Beyond the scope of this diagram is, of course, the sensible strategy to use multiple vendors. All major online publishers use multivendor approaches. While outages in any of these providers’ platforms are rare, there is a commercial advantage to working with multiple providers: You always have a stick to beat the other company with to maintain price.

I have broken my approach into three top-level priorities: price, support, and functionality.


For commercial operations, and in a playing field where all providers are roughly equal, price is a very important driver in your decision. There are six underlying cost models that appear frequently (not including free, which usually has some form of advertising sponsorship, such as that provided by Live365 or YouTube).


Traditionally, CDN billing was built on charging for each gigabyte of data transferred and for each gigabyte of data stored or hosted within the CDN’s infrastructure. While this is still common with smaller CDNs, the larger CDNs have set up resellers who can manage the small clients. Often these smaller resellers buy commitments themselves and charge a premium price per gigabyte, in return for flexible customer billing plans, such as pay as you go or prepay.


The larger CDNs have in turn moved to a model where most of their monthly charging is tied up in a monthly commit where clients pay a fixed fee each month based on an approximation of the data transfer they will use. If they exceed that commitment, the amount they are billed for the overage is considerably cheaper than it would have been without the commitment.


It is, in some cases, possible to restrict the excess to ensure that bills remain constant—and this results in a capped service whereby a limit is reached and streaming simply stops. Obviously, this can cause brand damage, and capped services are very unusual since they are common only for live events where the anticipated traffic volumes are unpredictable. If the cap is reached, a polite message is usually delivered to the end user saying “Servers are saturated. Please try again in a minute.” This message reinforces how successful the live event is in the same way that a sellout tour reflects well on a band.


As anyone who has ever bought a technical service will attest, the success of the relationship with the service provider is defined by the moment the service fails or when it is too complex to initialize.

The first complexity is often language. The major U.S. CDNs are wonderfully myopic about language. While they often employ regional business development teams who engage their customers with enthusiasm in the local language, once the contract is signed, customers are expected to “get with it” and learn English. The support centers and “global” network operations centers inevitably turn out to be run from the U.S. and rarely have language skills beyond English. If English is not your primary language, then be sure you test the CDN’s support services before you commit to any contract. When things are going wrong, communication barriers only add to the frustration.

Beyond this simple human interface level, there are a number of other factors that fall into the support category on the chart.


If you anticipate needing new services with a fast turnaround, make sure you have a service-level agreement (SLA) in place. It should guarantee not only fix times for faults but also provisioning times for new services. This is absolutely critical if you are attempting to offer live event services. Some CDNs want to “credit score” you before they discuss what you want: When they have a clearly defined document produced that indemnifies them against any error, they will push the go-live button, which could still take weeks for the engineers to activate. This is fine for long-term contracts, but it is absolutely useless when you get a phone call asking you to produce a spontaneous event that evening and your CDN just cannot mobilize in time. If that might happen to you, be sure you’ve arranged an agreement in writing and run tests with the CDN well before you get that phone call.


In addition to these soft/hard systems pain points, there are also a number of KPIs that address the ongoing management of your services. Real-time monitoring is often essential for managing campaigns where knowing who is on the service now can be mission-critical. You would be amazed how many CDNs cannot tell you this until several hours (or longer) after the stream has been watched. If real-time information is what you need, then ensure (don’t assume) that the providers’ dashboards offer what you need before you sign the contract.


While traditionally CDNs reported on the server interactions and took a network-centric view of the distribution, essentially reporting based on the servers’ logs, the latest systems use player-side logging. This means that each viewer’s player posts back a small packet of data about the viewer’s use, the quality of service, and so on. This post-back can potentially happen every second or two. Historically this produced too much data for any degree of timely analytics, and it also caused a storage and data management issue for the CDN. However, today huge amounts of data can be aggregated quickly and mined in seconds. The best thing about this type of analytic is that you get a real view of what your audience is experiencing, and this has led to an increase in the range of quality of experience (QoE) metrics. That is something that was impossible before—a little like measuring the satisfaction of a glassware mail order service by counting how many glasses you put in the post, rather than how many arrived at your customers’ premises unbroken.


Finally, if your service is mission-critical, you want to be proactive about knowing if there are any outages. While outages in the delivery of video on demand (VOD) are relatively unusual, live and linear services are more prone to faults. A good CDN will have a range of operational support service (OSS) integration options, such as SNMP traps, WMI indicators, SMS alerts, tweets, RSS feeds, or other similar notifications. This means that if you are running encoders at your own facilities and the CDN loses the connection to the encoder, you will be alerted immediately.


So now we move from the bones to the meat. The following functions loosely embrace the range of services that are available from CDNs. Obviously you will have a requirement for some, and perhaps all, of these features to be even considering a relationship with a CDN. Let’s break them out.


Many CDNs will be able to provide integration with ad servers for the entire array of ad formats and targeting. In some cases, the advertisements will be sourced and contributed to the CDN’s hosting infrastructure by the clients themselves. Many CDNs also have relationships with ad-sales groups and will be able to provide the advertisements along with a revenue share. These packages usually come with a campaign management tool and a way to track the advertisements as they are displayed. In my opinion, these relationships are often volatile, and with the exception of Google’s YouTube and Live365, they are rarely very profitable for the content providers, with complex expectations from the advertisers and low margins. However, in a few cases these models really work. When they do, the results can be extraordinary—giving rise to freemium models that can be quite profitable.


For many years, the industry spoke about convergence, and indeed H.264, MP4, and HTML5 are all results of that approach. But the reality is that with the plethora of competing devices, the market has, if anything, become strongly divergent in the past 2 years. It is important to understand your CDN’s strategy here. Some CDNs invest more and more in the quality of delivery of a smaller and smaller number of formats, while others invest in reaching as many formats as possible.

A good example of a technology that once was all the rage and now is almost universally unsupported is RealVideo. As we see the new HTTP-based adaptive bitrate technologies emerging, it’s easy to believe that over time only HTTP-based streaming formats will be supported. Personally, I think that time is a long way off. While browser-targeted streaming is a very important and big part of the market, so too is the emerging OTT market, and there are a number of devices that want flow control and don’t want to assume there is more bandwidth than required. (HTTP relies on over-provisioning rather than efficiency in the network.)

CDN Chart

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