When Should You Choose P2P?
You don’t want to be the first to test a new technology through each consecutive scaling barrier. Ask about any existing deployments and the number of concurrent users supported in each.
Another key metric for any solution is client distribution, which is the number of clients already installed and in use. Large client distributions are a good measure of the underlying technology, but in addition to the absolute number (and active number), it’s important to consider the geographic distribution of those clients as well. As with traditional CDNs, the geographic reach of a solution is a function of infrastructure, in this case, clients. And because network environments vary greatly in different parts of the world, knowing that a technology has proven effective from a global perspective ensures your users will have a good experience, no matter where they happen to be located.
Usability Questions
A usable client application must be well integrated into the comprehensive end-user experience. This means the application is polite to other running applications, is polite to other users on the shared network, and doesn’t interfere with the content owners’ branded experience. A useable client is small in footprint and memory use. A useable client does not impede other applications on the network or machine. A useable client does not present a heavy interface that disrupts the brand of the content owner. As a CDN typically operates invisibly in the background, content owners should expect peer-based systems to behave the same way.
To reach the broadest market, P2P technology will need to be integrated into hardware devices or software applications. Again, the usability of a client will dictate how realistic that opportunity is. If you ever want your content to reach the television, the client technology you select must be of a small size and "embeddable" into hardware.
Finally, usable clients must operate in any network environment, including those home networks behind network address transition (NAT) devices and firewalls. Personal firewalls should not block P2P traffic (or flag it as suspicious) and the P2P solution must traverse NAT devices effectively, given the pervasiveness of shared wireless home routers running NAT.
CDN Integration Questions
When evaluating a hybrid CDN solution, one key consideration is the underlying CDN architecture itself. Of particular importance here is the trend towards multiple CDN sources for content publishers. As the sophistication of providers has grown, many are using their own origin infrastructure to fill in the troughs and use a third-party CDN solely for peak management. Others are leveraging multiple CDNs to ensure minimally a dual vendor strategy, but also leveraging the best CDN for the various geographies they serve.
Most hybrid solutions fall into one of two categories; a dedicated CDN solution and a CDN-neutral solution. In the dedicated model, the peer-assisted network is vertically integrated with specific CDN infrastructure. The combined offering looks very much like a stand-alone CDN vendor and is often managed as such by the customer. When evaluating solutions of this nature, it’s important to evaluate the infrastructure elements as you would any traditional CDN in terms of scale, geographic reach, and capacity.
CDN-neutral solutions are designed to work with any third-party CDN that supports HTTP 1.1. This allows peer acceleration to leverage multiple CDNs concurrently and to accelerate several networks at once. This flexibility affords the customer the opportunity to bring a best of breed solution to bear, with best in class CDNs alongside best- in-class peer technologies. However, with so many CDNs in the marketplace today (dozens by some estimates), you will want to carefully evaluate if the solution has referenced working implementations with your vendor of choice or set aside additional time for testing.
As with any CDN, good reporting is key to getting the best performance out of your vendor and the most for your money. Peer-based systems have a unique advantage here, given the ability to measure the exact performance delivered to the end user at the client and, in the CDN-neutral solutions, the ability to present an unbiased view of the underlying CDN infrastructure as well.
But at the end of the day, it’s about performance. The ultimate questions focus on how much offload (expect good numbers), or how much more reliable and/or faster is the download. In other words, can this technology deliver the high-quality content your users demand?