I am setting up an RB2011 to share a 150Mbps internet connection between several small office tenants. What I would like to achieve is equal sharing between tenants under load, if e.g. one PC in tenant1’s LAN is downloading over HTTP, and a dozen PCs in tenant2’s LAN are all running torrent downloads and streaming videos and so on, both tenants will get 75Mbps each, regardless of how many PCs or connections each tenant has. Can this be done?
Sure, use Firewall/mangle to mark your traffic and queues to apply limitations on market packets.
http://wiki.mikrotik.com/wiki/Bandwidth_Managment_and_Queues