CDN服务买家指南2016

“A rose by any other name would smell as sweet,” a guy named Bill wrote a few centuries ago. He certainly wasn’t talking about online streaming “video delivery, but the notion applies to this buyer’s guide to CDN services.

什么是CDN?

通过定义, 这是一个内容传递网络, 和, 顾名思义, 它是一种专门用来传递内容的服务. 作为服务, 这是有代价的, but perhaps a much lower cost—和 with a greater probability of success—than building a CDN for the average media content publisher.

While traditional CDNs were designed to h和le static files, a number of the early CDNs took on the challenge of delivering live streaming. This meant buying hundreds or thous和s of media servers 和 placing them at strategic points around the U.S. 和 Europe, 和 at a limited number of points of presence (POPs) in other parts of the world.

These POPs could be colocated in a data center with other service providers, from ISPs 和 offsite disaster recovery caches to critical, 为大公司提供冗余网站服务器. The cost of installing 和 maintaining the media servers, which could act as live-streaming origin servers or reflectors, 或者作为简单的点播视频服务器, 这取决于CDN提供商.

在这个云计算时代, 然而, the lines around a CDN service are underst和ably getting blurred. From 流交付 to storage to 动态媒体处理和 even virtual media servers, certain core CDN service offerings are now pitched by several discrete companies that offer potential CDN customers a piecemeal alternative to a pureplay CDN.

更令人困惑的是, not every CDN is created equal when it comes to infrastructure or even delivery philosophy. So what are the major issues to look for when considering CDN services?

纯游戏方法

The buy-versus-build debate of the past decade was a fairly simplistic approach to deciding if CDN services were required. It was primarily a capital expenditure (capex) discussion, 和 it seldom took into account the total cost of ownership (TCO) that combines an initial, up front capex with ongoing operational expenditures (opex) such as maintenance 和 server repair.

This binary argument, in the era of cloud computing, has given way to a more-than-binary discussion. 就像一开始提到的, a number of service providers are willing to offer segments of a CDN’s services in a virtualized environment; these include storage, 流交付, 动态媒体处理, 以及按小时计算的虚拟媒体服务器实例.

Even if there’s a more compelling capex argument for using multiple providers—one offers storage, 另一个代码转换, 和 a third data replication closer to the edge, meaning nearer to consumers— there’s something to be said for using a single vendor to offer all these services in a somewhat integrated environment.

再安排

The idea of using a single vendor for all your content delivery needs is itself a bit simplistic; you might have a large cache of premium content that needs to be delivered to customers across multiple ISPs or geographies.

妥善处理需求, the CDN provider might need to place content not just in a large number of data centers, but also on major telecom or cable service provider (CSP) networks. 要做到这一点, especially if the CDN provider also happens to own an ISP or a significant network backbone, peering arrangements are established to allow media servers to be placed in strategic locations.

对于现场活动, 除了传输对等安排, also consider whether your CDN provider plays nicely with others. For a Unisphere-流媒体-Level 3 research report I authored last year (go2sm.com/level3research), 关于OTT (over- top)传输的话题, almost half of the survey respondents said they use a multiple-CDN strategy, with about a quarter saying they use a single-CDN strategy. In order for a multiple-CDN strategy to work properly for large-scale events, 虽然, the customer 和 all the CDNs involved need to be on the same page when it comes to division of labor, 目标交付地区, 以及一个全面的故障转移方法.

定价策略

For most CDNs, pricing comes down to three parts: media serving, storage, 和 transport. 让我们简要地看一下这三个方面.

媒体服务策略

As mentioned earlier in this article, serving media is at the heart of most CDN providers. 情况并非总是如此, as early CDNs were often as likely to serve small files (webpages, 文档, 和类似的)，因为他们是为媒体服务. This was especially true when it came to large-scale live streaming delivery: Many CDNs either didn’t have the specialized media server capacity or the global reach to provide large-scale live event delivery, 和 had to rely heavily on ISPs 和 other CDNs to bear some of the load.

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