Independent personal services may be taxed by the other state if a fixed base exists or prolonged presence occurs. Income from independent personal or professional services is taxable only in the taxpayer's State of residence except where the taxpayer has a fixed base in the other State, in which case only income attributable to that fixed base may be taxed there, or where the recipient's presence in the other State meets the treaty's extended presence threshold, permitting that State to tax the income arising from those activities.