Relation between Quantization on Null-surfaces and the Characteristic Initial Value Problem ?

We consider quantization along null-surfaces. We note that null-surfaces are characteristic surfaces, which requires a diierent treatment than the usual equal-time Cauchy initial data quantization. We examine this for quantum eld theories and show that by considering quantization on null-surfaces as a characterisitc initial value problem, we can avoid initial relations-constraints-between the elds. We are also able to show that the Green's function obtained is identical in form to that for equal-time quantization.