something is still wrong with my ubuntu PC. If you see my previous post, It shows ffmeg built by me but I thought I have missed some options on configure so I have it re-compiled following the instructions. It did not help! FYI, with my windows pc I put it in ad-hoc mode, and same with the N810, knots2 works very well! must better going through the AP (strong signal! they are close). And when we have two servers in the network (I tried not in infra mode), knots2 will pick one right away, there is no option to select.