I have asked to test an VPN phone for home Users. I have a BT adsl broadband at home which is going into a cisco 2900 switch. Port One is connect to the computer port 3 is connected to the Avaya VPN phone this work's. The quality is not very good, so the question is could I have qos on Port 3 which is connected to the phone?
QoS is always important when dealing with VoIP, but as you only control the flow as traffic leaves your switch at home and then at the remote end, you will always be "fighting" the internet for bandwidth/priority if your ADSL line is a home user setup. The QoS on your local switch will help guarentee/prioritize the traffic that leaves your home network, but after that, it's a free for all untill it hits your remote end. If the 2900 is the XL, then you will have scheduling capabilities, see below for more details.
In summary, yes, apply the QoS at your end and the remote end, this my help the "quality" of the call, but you also need to factor in the Codecs you are using and that you are using VPN protocols to get to your remote end.