Choosing the right content delivery network
By Sharon Florentine
Sharon Florentine is a freelance writer who covers everything from data center technology to holistic veterinary care and occasionally blogs for Rackspace Hosting.
Welcome to Generation Now. Today’s users want information in an instant. Make them wait more than a second or two for your webpage to load and they’ll surf over to the first competitor who feeds their demand for instant gratification.
Using a Content Delivery Network or Content Distribution Network (CDN) to quickly load static elements of your site to hasten access can deliver quicker gratification for customers. And stickier eyeballs — and greater profits — for you.
Basically, a CDN is a number of highly optimised web servers located around the globe, explains Joost de Valk in an article posted to Yoast.com. Though de Valk’s article deals specifically with using a CDN to speed performance of Wordpress sites, a CDN is beneficial for almost any organisation with a Web presence, in any industry.
Users expect that all elements of a site will load in an instant: web objects including text, graphics, URLs and scripts, downloadable objects like media files, software, documents, e-commerce applications, portals, streaming media and the ubiquitous social networks.
Put another way, CDNs can benefit heavily-trafficked sites, regardless of topic; video sites or sites that offer other types of downloadable files and sites promoted on Digg.com or other "trending" web sites. CDNs work by distributing static data to geographically disperse servers worldwide. When users access your site, static content will be delivered from the server that's closest to their physical location using Pull URLs that point to a specific directory on your servers. This leads to huge performance improvements for sites that have visitors from all across the world, de Valk said.
If you’re considering using a CDN, there are some questions you must answer for yourself before you even pick up the phone to contact your potential provider. First, you have to know what kind of content you’ll be delivering.
As author Dan Rayburn, in this article on SteamingMedia.com points out, you must be able to tell a potential provider: whether you need on-demand delivery, live or a combination; whether you are supporting Flash, Windows Media, or multiple video formats; the number of hours of content you currently have and how many hours you’ll be adding each month; the location of the majority of your viewers; your business size (i.e., SMB? Large enterprise? Major media corporation or small provider of other services) and how much content you’re currently delivering and expected quarterly growth.
Rayburn advises organisations to delve even deeper, and make sure to ask the following four questions of any potential CDN provider. The first question involves how to measure network performance. Rayburn notes that performance can be measured in many different ways.
“Some measure it based on things like customer service and service level agreement (SLA) terms. Others base their assessments on the physical speed of the network and delivery service. While this is common, it’s important to know how to measure effectively,” he said.
When gauging network and service delivery performance, your organisation should take into account a combination of many factors including price, customer service, SLA and a guarantee that you’ll be able to access and upload your content at all times, Rayburn said.
The second question to ask is ‘How will I be compensated for network outages?’ Sure, every provider will tell you they have a 100 percent uptime guarantee, but in reality, network outages happen all the time, and streaming media SLAs typically do not go into detail as to what exactly is guaranteed, Rayburn said.
“They may be guaranteeing only that the server will be up 100% of the time—not that the network will be. Typically, SLAs are very generic when it comes to streaming media delivery services. The only important question you need to ask is: how will you be compensated in case of an outage of the network or any portion of its hardware that affects you?” he said.
"It’s extremely important to monitor your network uptime, since many service providers’ contractual fine print states that the provider only compensates you if an outage is of a specified length of time or if you actually notice the outage and request monetary recompense."
A third question to ask is whether or not the provider charges for “bursting overages.” A bursting overage occurs when you push more bits of data than you paid for in your contract, but it’s more important to know how providers charge for the delivery of data, Rayburn said.
“Every large-scale CDN charges for delivery of video, via streaming or download, based on two metrics. One is the total number of megabits per second (Mbps) sustained at any given time. The other is the total number of gigabytes (GB) delivered over the network in any given month. These are two very different metrics with very different overage charges,” he explains.
Most customers’ contracts charge based on GB delivered per month, and if overages do happen, the service provider often charges a lower per-GB charge to encourage customers to drive more traffic to their sites.
“If you are paying on a per-GB-delivered model, don’t ever agree to overages. Ask to be given a lower price based on growing your business,” Rayburn advises.
The other way CDNs charge for video delivery is on a per-Mbps-sustained model, whereby you pay for traffic volume at a specific point in time, not the total bits pushed. This model allows providers to charge overage fees on any traffic that occurs above the volume of Mbps sustained that you commit to, he said. It’s important to compare the two pricing models and determine which is best for your business.
The fourth question to ask is, "What does the service provider support in the way of delivery?" Rayburn said. Does the provider actually support streaming video? Don’t assume they do; many providers use the term without a proper understanding of what it means, he said.
“Some service providers use the word ‘streaming’ to sell and promote their services when, in fact, they don’t offer delivery from a media server, but rather deliver everything via progressive download from a web server,” Rayburn said. “This may suit your needs if you want progressive downloads, but if you require actual streaming or a combination of the two, you’ll want to make sure the provider supports it.”
There are, of course, numerous other questions to ask any provider, but these four in particular are applicable to nearly any organisation, regardless of their business and technology needs. Getting satisfactory answers can mean the difference between success and failure, and form the basis of your company’s cloud video delivery services.
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