First, you posted this in the API section. This is meant for help with the API, not stream support.
&cdn is just the flag for the CDN (Content Delivery Network) setting in a URL.
Level3 provides CDN service but the past few days it has been experiencing issues. (http://www.neowin.net/news/level3-suffering-major-outages-effects-are-felt-worldwide ) If you access the site normally and have a problem you should figure out what that problem is instead of manually choosing a CDN PoP (point of presence). They automatically place you on the closest PoP they can. They also most likely account for saturation if they have multiple PoPs in your area. If buffer continuously to your local PoP I suggest reaching out to twitch by reporting a video issue with any stream you have an issue with. Also, if you get no issue using a PoP you set manually maybe you should complain to your ISP about having a bad network and crappy routes.
TL;DR - I don’t suggest try to fix something you don’t understand using a bypass. Figure out the actual problem and solve that.
PS: Using a proxy or VPN in another nearby region will probably get you placed on a CDN close to the VPN/Proxy.