Independent personal services: generally taxable in resident state, except fixed base or extended presence allows taxation elsewhere. Income from independent personal services of a resident is taxable only in that resident State, except where the resident has a fixed base in the other State-then only income attributable to that fixed base may be taxed there-or where the resident's presence in the other State exceeds an aggregate duration threshold within a twelve month period, in which case only income from activities performed in that other State may be taxed there.