栈的状态

了解互联网服务提供商如何, 电信公司, 发布商, and online video platforms fit into each layer of the online video stack is crucial to making smart purchasing decisions. What follows is an overview of what fits where and how the various players' roles are changing.

什么是在线视频堆栈?

First, let me share how I am using the concept/term "stack" through this article. The open systems interconnection (OSI) stack is a relatively familiar model used worldwide by network engineers to define roles between functions within the network, 将它们组合在一起, 通过这样做, helping to define "interfaces" between them all (protocols) that help create interoperability between vendor implementations; it's unlikely you are reading this if this 信息 is new to you.

I am going to explain a little more about the CDN operator comparisons I have included and what I mean by them, 但在深入细节之前, we need to also fix a perspective on the CDN aspects we are focusing on here. It's important to note that not all 发布商 handle video; many handle games services, 软件更新, 网页代理, 以及应用程序加速.

为本文的目的, I am looking at 发布商 that provide internet video and audio delivery services among their offerings (both on-demand and live). I am interested in the ability of a CDN to deliver live streaming in particular as a prequalifier, since on-demand services are neither terribly complex nor do they require much more than a basic hosting and distribution architecture. 确定, 按需托管有很多不好的地方, 还有很多方法可以把它做好, 但它通常只是购买带宽, 架, 和服务器. 要增加容量，可以添加更多的这两种类型.

的能力, 实时地, cache video-on-demand (VOD) content "live" as copies of it are transferred from their sources to the edges and "through" the cache (so later copies can be delivered from the cache) also helps highlight how high-speed telecom networks are very much at the heart of well-run networks. A bad network in a VOD CDN will cause problems for the initial users of the content who are playing it from source. 然而, 后续的用户, 查看缓存, will probably not suffer as much from the consequences of bad networking since the cached content is "closer" to them. 鉴于这将是大多数用户的情况, 在一般情况下, 建立低成本的视频点播CDN相对容易, 即使使用public, 忙, 缓存之间的廉价互联网路由.

这些天, 然而, even the most congested routes are generally capable of offering a perfectly usable file distribution network, far above the capacity requirements of the general public's need for videos distributed using even simple web services to offer "progressive download.“YouTube就是一个证明. While there is still some way to go from a broadcast perfectionist's perspective, the internet has evolved so far in the past decade that the value proposition of localizing servers to ensure delivery and quality at lower cost and higher SLA than the alternative (which would appear to be simply putting lots of servers online on-site at the source of the stream/publisher's offices and serving from there) has become considerably less powerful as a proposition over the past few years.

This is interesting when you think back 5 or 10 years to the number of 发布商 that were almost "trading off" the number of edge cache locations they had.

Live streaming places a different and more sophisticated load on the network designers and operators: sufficient capacity with flexibility in configuration, but at the same time not over provisioned/underutilized to the extent that it is uneconomical. Live streaming architecture is very involved with telecoms and not just limited to store and forward internet content delivery between servers and eventually end users. Tight Layer 3 (IP) network operations are therefore at the core of live streaming offerings at scale. 发布商 still buy from Layer 2 and Layer 3 电信公司, and the 电信公司 buy into peering facilities. 他们购买的越多，他们的直接成本基础就越低.

今天, 好, 低成本的IP连接随处可见, and the trend is toward longer backhaul of IP from users to fewer, 联系性更好, centralized data centres managing the session and application and keeping the majority of the functionality in one place. In its pure form, this has been nicknamed the "death star" architecture, although it is more
properly/ traditionally called a "hub and spoke" architecture. The downside is that a local problem at the hub takes out everything where in a distributed architecture there are fewer risks of centralized points of failure. The upside is you can centralize and optimize all your maintenance and support issues. 值得注意的是, 在所有高可用CDN服务架构中, the hub itself is usually a geographically distributed range of services clustered to act like a single central hub to ensure continuity in the event of even the most significant problems.