Taxation of independent personal services: resident state generally exclusive, but other state may tax where fixed base or extended presence. Income from independent professional services performed by a resident is taxable only in the resident State except where the person has a fixed base in the other Contracting State - in which case income attributable to that fixed base may be taxed there - or where the person's aggregate presence in the other State meets the applicable stay threshold, in which case only income from activities performed there may be taxed by that State.