Behind the scenes: How Content Delivery Networks leverage optimization technologies
Establishing a reliable web presence is the best way to maintain competitive advantage for your business. Large websites often rely on Content Delivery Networks (CDNs) as an effective way to scale to a larger and more geographically distributed audience. A CDN acts as a network of caching proxy servers, which transparently cache and deliver static content to end users.
There are many CDN providers to choose from, but what makes Internap unique is the combination of optimization technologies that we employ. Let’s take a behind-the-scenes look at how these technologies complement one another and work transparently to improve the user experience and accelerate performance.
You may be familiar with Managed Internet Route Optimizer™ (MIRO), Internap’s route optimization technology that forms the basis of our Performance IP™ product. MIRO constantly watches traffic flows, and performs active topology discovery and probing to determine the best possible route between networks. After our recent revamp of MIRO, some of our busiest markets are exceeding half a million route optimizations per hour, resulting in significantly lower latency and more consistent performance.
Our CDN also employs a proprietary TCP congestion avoidance algorithm, which evaluates and dynamically adjusts to network conditions. It ensures that short data transfers, such as HTML, Javascript libraries, style sheets and images occur as quickly as possible, while larger file downloads maintain consistent throughput.
Finally, the CDN’s geographic DNS routing system sends requests to the nearest available CDN POP based on service provisioning, geographic proximity, network and server load and available capacity.
All CDN transactions begin with DNS
When a client issues a DNS request to the CDN, DNS routing is handled by a routing methodology called anycast. Internap has a large deployment of CDN DNS servers around the globe, and with anycast, we use BGP to announce a prefix for our DNS servers in each of these locations. The client’s request gets routed to the nearest DNS server based on BGP hop count.
When a DNS request is received, MIRO observes this DNS activity and immediately begins probing and optimizing to find the best possible provider for that DNS traffic. The CDN DNS system evaluates the request and responds with the address of the nearest available CDN POP. The client then establishes a connection and sends a request to an edge cache server in that selected POP. Once again, MIRO observes the network traffic, and immediately begins probing and optimizing to find the best possible provider for the network traffic.
If the requested content is in the cache, then the cache server begins sending it. TCP acceleration takes over and begins optimizing the TCP connection, which ensures CDN content is delivered as quickly and smoothly as network conditions allow. If the requested content is not in the cache, then the cycle repeats itself, but between the CDN edge server and the origin of the content.
The best experience is achieved with a globally distributed origin that employs geographic DNS routing, such as Internap’s distributed CDN storage solution. With CDN storage, content can be replicated in up to 5 different locations across the globe, and the CDN DNS system routes the request to the nearest available location. MIRO also optimizes the experience between the edge and origin servers, both for the DNS request and the content retrieval. TCP acceleration ensures that the transfer happens with the lowest latency and highest throughput possible.
With the recent revamp of Internap’s HTTP content delivery platform, we’re continuing to maintain our commitment to performance. We have upgraded our cache servers to use SSDs instead of hard disks, and added some new performance-oriented features, such as the SPDY protocol. All of these new capabilities will further enhance the user experience and accelerate performance.
