I've been searching for this and from what little I've found modern day routers try to balance internet bandwidth as fairly as possible. (I'm using a Asus AC66U myself)
For example, if I have a 100 Mbit internet connection and two clients want to use maximum bandwidth the router tries to distribute 50/50 between these two. And if three clients are trying to use as much bandwidth as possible then it will be divided 33/33/33.
But it feels like this fair distribution is not always the case so can someone help me understand the following:
How is this distribution performed by routers in more detail and which scenarios cause this theoretical bandwidth distribution to fail?
Thanks!
Best Answer
Quality of Service doesn't evenly distribute services based on the number of clients requesting the data, rather, it rations the bandwidth based on the services being requested.
Example; one user is requesting Netflix, the other is just surfing web pages. If streaming video is higher on the list of priorities than HTML, then the first user's data will be handled first.
Other factors are often considered in QoS; latency, bandwidth, jitter, and reliability. If a service has a high response time (high latency/ping), then it may get moved down the list.
As far as the title question, a router without QoS wouldn't decide bandwidth distribution. It would just be first come first served.
How To Geek has an easy to understand breakdown of the concept:
http://www.howtogeek.com/75660/the-beginners-guide-to-qos-on-your-router/