Back in May, Sandvine’s CTO Don Bowman talked to Ars Technica’s Jon Brodkin, about why Netflix performance improves on some ISPs when using a VPN.
That above linked Ars Technica article does a great job at tackling the improved quality some users experience when using a VPN, and I was really hoping to never have to talk about it again.
Over the past few days however I have received a couple emails from people looking to discuss this topic yet again. After doing some digging the questions are emerging because of one Netflix subscriber’s blog post that highlights how they get a higher bitrate stream when using a VPN as opposed to their Verizon connection.
So in the hopes of not having to revisit this again in five months, we will once again attempt to explain why in some circumstances a VPN may improve your Netflix (or other video providers) experience.
Before we dig deeper, the two key things you need to know about packet delivery on the Internet are as follows:
1) The sender chooses the path for all packets
2) Networks are not normally intelligent enough to route around congestion
In the image below, we can see two people attempting to access Netflix in the same household.
User A as represented by the blue line is using a direct connection from their ISP. As you can see the path they have to travel is far shorter than User B, but because the sender (Netflix in this case) has chosen P1 and P2 as the paths for the user, they are likely experiencing a lower bitrate video because of congestion between the peering provider and Netflix’s Open connect CDN.
For those readers, who may immediately jump to the cause of lower quality video being a consumer ISP throttling traffic, know that even the CEO of Netflix doesn’t think this is the case.
So why might this congestion be occurring? It is likely being caused be a number of commercial and technical factors between the peering providers, content providers, and ISPs. We’ve talked about these factors a number of times on this blog, but the basics of it are there are commercial disagreements between those three parties about who should pay for capacity and this inhibits the ability to deliver high quality video all of the time.
So why might User B who has a longer path to take because they are using a VPN have a better experience? Well, User B’s VPN is paying for a higher quality, uncongested link (P3 and P4 in this case). The sender (Netflix) still chooses the path the video takes, but because they are only connected via uncongested links, they are able to achieve a higher bitrate of video even with the farther path. P3 in this case might even connect to both the consumer ISP and Netflix Open Connect, but Netflix may make the choice to use that path in order to reach the consumer ISP. Who provides these links (p1,p2,p3, p4)? Companies like Cogent, Level-3, Tata, nLayer… These are the ISP’s of your ISP.
I should point out that in the image above the VPN chose the North server farm, but a number of factors may have caused it to choose the south farm instead. If that had of happened User B might have gotten access to a server farm in a different time zone, potentially even shifting usage from off peak hours to peak hours or vice-versa which could also positively or negatively impact video quality. If you use a VPN you can always use a website like http://www.whatismyip.com/ to determine where servers think you are coming from.
So will a VPN will give some people a better video experience? Yes. Will it improve video quality for the vast majority of subscribers? Likely not.
For almost a year now, both on this blog, and in our Internet Phenomena Spotlights, we have been talking about how quality is an end to end process and how many of the issues faced by subscribers are actually caused by commercial disagreements over who should pay to carry the huge amount of Internet video subscribers now demand. This likely isn’t an issue that will disappear anytime soon, and our hope is that before subscribers go pointing fingers at their ISP or the video provider (who they both pay a monthly fee to), they understand that the video delivery is a complex issue, and that in reality no single party is to blame for the quality issues they may experience.