Hello,
i would like to ask u, having 3Mbit/384kbit network, about 40 PCs (usually 10 active).
I would like to guarantee network bandwidth for VoIP telephones.
What do u suggest?

My idea: on mangle mark packet for IP telephones, give them some priority and no download/upload limit on queue tree. Then, mark other traffic and give them max 2,5Mbit download 256kbps up ..

Other idea?

Yes, absolutely great. then the use of voip can be max and the network(except voip, can be limit with max limit). u can just use simple queues for this.