Right. But I supposed by hotspot/ad-hoc, we were talking about the link layer possibilities only. hotspot is also about MAC layer only as well. IP runs on top o

Right. But I supposed by hotspot/ad-hoc, we were talking about the link layer possibilities only. hotspot is also about MAC layer only as well. IP runs on top of that. However, the difference is that, in AP/client mode, all nodes need to associate with and be able to talk to an AP; while in ad-hoc mode, every node is equivalent and they can be as distributed as they want. For ad-hoc routing, there're olsrd, batman, etc. They are really cool :-) We used to use Android devices to test different scenarios of ad-hoc applications. But none of current mainstream devices support ad-hoc mode any more. On contrast, iOS devices can still join (although not create) an Ad-Hoc network, which is ... ironic.