QoS - Upstream Bandwidth

Question

Just wondering if there is any more info about this setting. I really don't have a problem to fix, just seeking a better understanding regarding this setting.
I have myself and many clients on SIP based hosted VOIP (Vocalocity) and this has helped improve call quality.  We add the mac address for each phone and give it high priority.
In most cases when there is a multitude of upstream speed it seems that manually setting this number to below the actual speed really helps to keep the PCs from hogging the upload speed and thus preventing latency.

Answer 1

1. It helps a lot if you post the router you use. Different models have different settings.
2. Generally, it's correct what you see. The auto setting tries to use the full bandwidth available. Of course, bandwidth usually varies with most ISPs thus you will probably see more packet loss in moments when the real bandwidth is less (i.e. usually due to other customer's traffic).
Thus if you set it to a lower value it will reduce packet loss because the total upstream traffic won't hit the ceiling of what's actually possible at that moment.
Of course, on the other hand a lower value won't really let use the total available bandwidth at moments when there is more.
Example: 8 Mbit/s DSL line. Speedtests show varying 4-5 Mbit/s throughput, but never or very rarely below 4 Mbit/s.. Thus, if you manually set the upstream bandwidth to 4 Mbit/s you will prevent the connection from overloading. Little packet loss and little latency. Setting it higher will increase the chance of overloading the line.
The main problem is that the router has no way to know what bandwidth is really available at any given time. All it can do is to guess from what it saw before.