Thursday, January 27, 2011

Netflix Performance on Top ISP Networks





Hi there. This is Ken Florance, Director of Content Delivery here at Netflix.
 
As we continue to stream more and more great movies and TV shows, we find ourselves in the unique position of having insight into the performance of hundreds of millions of long duration, high-definition video streams delivered over the Internet.
 
The throughput we are able to achieve with these streams can tell us a great deal about the actual capacity our subscribers are able to sustain to their homes. In the charts below, we’re using a time-weighted bitrate metric to represent the effective data throughput our subscribers receive over many of the top ISPs.
 
Currently, our top HD streams are about 4800 kilobits per second. Clients may switch through a number of bitrates as they ramp up to the highest stream, or shift down from the highest stream if they cannot sustain play at that rate due to throughput constraints. No client would sustain a 4800 stream from start to finish (there would at least be a few smaller streams averaged in for startup) but the higher the sustained average, the greater the throughput the client can achieve, and the greater the image quality over the duration of the play.
 
As we use a number of CDNs, and our clients can adapt to changing network conditions by selecting the network path that’s currently giving them the best throughput, Netflix streaming performance ends up being an interesting way to measure sustained throughput available from a given ISP over time, and therefore the quality of Netflix streaming that ISP is providing to our subscribers. Obviously, this can vary by network technology (e.g. DSL, Cable), region, etc., but it's a great high-level view of Netflix performance across a large number of individual streaming sessions.
 
In the metric below, we’re filtering for titles that have HD streams available, and for devices capable of playing HD streams (which also filters out mobile networks), to highlight what’s achievable in terms of HD performance on the various ISP networks. As you can see, Charter is in the lead for US streams with an impressive 2667 kilobits per second average over the period. Rogers leads in Canada with a whopping 3020 kbps average.
 
We'll update these charts monthly, and we welcome questions, comments and suggestions to help improve our understanding of Netflix performance on top ISP networks.