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Buyer's Guide: Content Delivery Networks

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Then again, these semantics are quite feasibly arguments for pedantic technocrats (such as you and me), rather than having any bearing on the real world today. Even so, it is naturally a good idea to try to get a long-term view from your CDN about its “religion” with regard to the future of formats. Otherwise, you could find that you suddenly face being turned off because of the CDN’s own strategy.


While all CDNs with audio and video capability will offer hosting and distribution for on-demand content, not all CDNs will support live events. If you ever might need a live service, make sure the CDN has that capability.

We mentioned earlier that consideration should be given to the time it takes to set up a live service and any SLA the CDN may offer with that. Another consideration for the live services is the proximity of the entry point. If you are based in the Middle East and your CDN’s live entry point server is in the U.S., you could be subject to considerable quality of service issues on the link between your encoder and the entry point. If that link performs badly, then all recipients of the stream will see the stream badly. CDNs are often dubbed “garbage in, garbage out” systems since all they do is split and distribute a live stream: If the source is poor, then there is nothing the CDN can do about it. Make sure your CDN has a local entry point, and test it before you sign a contract. You may need to put in a private line, and this could tie into the CDN’s willingness to host third-party technology in a co-location facility. Some CDNs will embrace this as second nature, while others will react to being asked as if you were a hacker breaching every security protocol ever devised!


Transmuxing is the rewrappering of encoded video from one format’s transport container to another. In essence, transmuxing is a very lightweight service that can be done on-the-fly in the CDN—it enables the same piece of video to reach multiple target devices.

Transcoding is the process of taking an encoded source video and re-encoding it to a different codec profile. Transcoding is not a lightweight service. While CDNs increasingly offer transcoding of on-demand content within their OVP proposition, this transcoding can take some time since the processes are queued up against finite resources of transcoding machines. Very few CDNs offer transcoding of live streams. In fact, there are a small number of cloud-based third-party providers emerging to provide this service as a specialist proposition. If you think you need live transcoding, you may do well to review your workflow design to see if you can do this yourself. The CDN may discourage you from using its platform by saying, “Yes, we can,” but then providing the service at a prohibitively high price point.

Transrating is the newest in-network technology on the block, and it essentially involves taking a high bandwidth source and stripping out frames and “quality” to effectively reduce the bandwidth required by the stream. So, for example, you could send the CDN an HD source at 2Mbps, and the CDN could transrate that source down to a mobile 250Kbps. It’s not quite the same as transcoding, so it has a lower overhead to the CDN. I have not seen any very mature models in play, although I am aware they exist, so I am not yet sure how transrating is being priced and offered.


Another format-related function that should be explored as you look at the CDN contract relates to the VOD content services: Some CDNs have famously had upload servers only in specific locations. I know of a large U.K. broadcaster who struggled for years with a well-known U.S. CDN because its upload servers in the U.S. were poorly provisioned. This broadcaster produced news, and it would sometimes take an hour to upload a 15-minute broadcast. Not good. If such delays are critical to you, make sure you test the CDN’s upload capability rigorously before you buy. Upload as many files as you can in parallel. Do this at peak local times as well as peak U.S. Eastern and Pacific times.


You may also want to explore if the CDN provides redundant backup of your content. By nature a CDN replicates VOD files internally, but this cache will be flushed regularly. If the master store in your office is lost, a proper backup program in the CDN could save your prized asset. Some CDNs do guarantee your content, while others don’t. Often CDNs don’t charge for content storage (although I have seen a resurgence of this billing in the past year). I would imagine that when you do pay, you are more likely to have a guarantee that the CDN will maintain a backup of all your files.

There are a number of other functions that will be available from most CDNs, although each will implement these in a slightly different way.


Outside the online video sector, web acceleration is what CDNs are all about—essentially proxying webpages to meet high-demand traffic. Not all CDNs offer streaming services, and not all CDNs offer web acceleration, but they are usually part and parcel of the same proposition.


A relatively simply service to introduce, geoblocking can be an important feature if you want to control access to content by region. The accuracy of the databases used varies, but typically a good geoblocking system can actually lock the content to a particular city. Most geoblocking systems can be worked around using virtual private networks (VPNs), but as a first defense typically they are good enough. Interestingly, geoblocking is a prerequisite for major broadcasters since their content deals are usually highly restricted to specific territories.


Essentially a fancy term for a content management system, CDNs have developed or acquired online video publishing platforms over the past few years that provide a GUI for upload, conversion, metatagging, analytics, and more for each video item. The typical OVP also provides multiple player interfaces for each target device. This is often beneficial to the content provider since the OVP does all the work keeping up with devices and presentation layer technologies, leaving the content provider to create content. The downside is that your content can look a little like everyone else’s since the overall feel of the presentation layer is often common to all the CDN’s clients, despite its best attempts to make the players customizable.


We mentioned this earlier in the context of live streaming, but there may be myriad reasons why you want to put your own servers or equipment in the CDN infrastructure. Some CDNs will embrace this, while others will most definitely not allow this. As the cloud emerges as a business model and as CDNs explore their own opportunities in the cloud space, some CDNs are beginning to offer Infrastructure as a Service (IaaS) propositions where you can pay for computer power by the time period and run your own applications on the network’s infrastructure. While fledgling at this stage, and I anticipate it will have the mid-term effect of confusing CDNs about their own focus, I think the long-term game here is obvious. Amazon’s EC2 has given small providers low-risk, low-cost infrastructure options that enable them to scale their streaming on an ad hoc basis. If the combination of IaaS with deep in-network distribution is attractive for your application, then CDNs could provide an interesting proposition. You will need to explore this at a senior level with most CDNs though: This stuff is far from productized today.


DRM is file-level encryption. It’s a complex beast to set up, so if your CDN offers it, and you feel you need it, then it is probably worth using the network’s DRM. However, there is one major consideration: Once a CDN encrypts your content with its encryption keys, you are very much tied into it. Ensure you keep an unencrypted copy in your own facility, and bear in mind that if you change CDN/DRM vendor, you will need to re-encrypt everything.

Conditional access is more straightforward. It’s essentially encrypting the channel over which the content is distributed so a user has to authenticate to get access. But once the file reaches the viewer, it could potentially be stored locally without encryption. This results in lower overhead in terms of technical configuration, and the files themselves are not encrypted, which means there is less lock-in. HTTPS and SWF verification are examples of conditional access technologies.

Both DRM and conditional access can be very useful in terms of giving content providers confidence that the best possible plan to protect their rights is being put in place. However, care should be taken if anyone tries to sell these services as an “absolute protection” since neither can (yet) insulate a provider from a committed pirate.


The final consideration should be one of the most fundamental ones you undertake. There are large global companies with huge resources and significant ranges of services and facilities. There are also many smaller boutique providers who may resell a larger company’s service but provide a different attention to detail and focus on their clients, or they may run their own infrastructure locally within their country. These so-called regional CDNs can often match the pricing of global players and provide much higher standards of service, and they often benefit from agility in their response to your demands. However, since they are often limited in resources and cash flow, they may also be unable to rapidly roll out new technology.

The most important thing to consider is your audience: If your audience is within a single region and only needs one format, then a regional CDN will probably serve you better than a so-called global one. If you go with a regional CDN and the audience profile changes to include an increasing number of international viewers, however, you may find that factors such as latency cause problems, such as startup delays and poor QoE.

As you can see, there is no quick and easy way to choose a CDN, but I hope this article helps you understand, at a high level, some of the considerations you should undertake as you make that decision. Feel free to contact me if you need specific advice.

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