Isn't iftop for a single interface? This can be a netflow(s-flow,etc) collector and thus give data about an intersection of links. This gives you the chance to add cpu and memory overhead to your switches and routers and also sampled data to draw dubious conclusions from! (Sorry, bitter ex net-eng. Modern data center speed and data volume are no place for sampling IMO. ASIC buffer vs microburst = hard to find badness.)