Input tax credit allocation: HO may use ISD or issue invoices to BOs, with valuation rules for full ITC. HO may either distribute ITC for common input services to BOs via the Input Service Distributor mechanism (requiring ISD registration) or issue tax invoices under section 31 so BOs can avail ITC; distribution or invoicing is allowed only where services are attributable to or actually provided to the BOs. For internally generated services, where the recipient BO is eligible for full ITC the invoice value is deemed open market value under rule 28; omission of specific cost components does not alter that deemed value. Employee salary need not be compulsorily included in value where recipient is not eligible for full ITC.