Westell A90-750022-07 - How to set up QoS/prioritize my internet connection?

I may not be able to offer too much help, but can give you a general idea of how QOS works and offer some suggestions.

All DSL modems or cable modems have a transmit buffer built into them. When your PC sends a packet to the Internet, it reaches the modem which places the packet into the buffer. This is a good thing. However, your Internet link is provisioned at a fairly slow speed compared to Ethernet. So, your PC can send a lot more data to the Internet than your link can handle. This bottleneck can cause packets to queue up inside of the modem's transmit buffer. If the situation goes on for long enough, the transmit buffer will completely fill up. So consider the following:

Suppose your modem has a 1MB buffer and your DSL line is configured for 1Mb/sec upload speed. At 1Mb/second, it would take 8 seconds to send all of the data stored in a 1MB buffer. (1MB = 8Mb, 8Mb/1Mb/s = 8s) So, when the buffer is full, a packet arriving at the back of the queue would have to wait in the buffer for 8 seconds before being sent out to the Internet. This would be catastrophic. Most TCP connections could not stand that much latency, and the browsing/gaming experience would be terrible. It is worth noting that your modem probably only has like 64KB of memory for a buffer, but still that would add 500 milliseconds of latency in our example.

QOS gives you a way to identify priority traffic and move it to the front of the queue. So even if there is 500ms of traffic queued up, if a priority packet arrives, it gets moved to the front of the queue.

Your modem offers some granularity for the configuration. Admittedly, I don't understand everything in the GUI, and I haven't read your modem's manual, but here is what I have gathered and some suggestions:

In order for QOS to work, you will need to configure your WAN upstream rate to a value lower than what you are actually able to reliably get. For example, if you are provisioned for 1Mb/s, but can only reliably get 896Kb/s, you should set this value to ~90% of that, or roughly 800Kb/s. You will lose some absolute maximum throughput, but will make your QOS settings more reliable.

Your modem can prioritize traffic into 7 classes. We'll be interested in the AF classes. What you will want to do is create a filter rule that will catch the traffic generated by your PC and place it into a class of service that is higher than the one for your girlfriend's laptop. For example, create a rule matching the MAC address of your desktop and placing it into AF4, while your girlfriend's laptop will be in BE. You could even reserve some bandwidth for AF4 by putting a value into the "committed info rate" field. On the filter rule screen try something like this:
Interface direction: To WAN
SrcMacAddr: Your desktop's MAC
DestIPAddr, SrcIPAddr: 0.0.0.0 (according to the help on the screen, that will disable matching on those fields, which is probably what you want)
DestIpPortStart/End/SrcIPPortStart/End - all zeros
Protocol: Any
Class of Service - AF4, or some priority higher than Best Effort

Give that a try and see what happens. You might also try putting in a rule for your girlfriend's laptop to place it in a lower queue, like AF3.

One other thing to check. I would bet her laptop is uploading a lot of data. Are there any Peer2Peer applications running on it? If so, configuring them to throttle their upload might help.

Hope that helps

--Russel