Taxability of services between distinct persons clarified: ISD optional; invoice value deemed open market value when recipient has ITC. The circular clarifies that where a Head Office procures input services from a third party but those services are attributable to Branch Offices, the HO may either distribute the attributable input tax credit through the Input Service Distributor mechanism (subject to mandatory ISD registration) or issue tax invoices to BOs; ISD use is not mandatory. It further provides that where a recipient BO is eligible for full input tax credit, the invoice value declared by the HO is deemed to be the open market value of internally generated services, irrespective of inclusion of particular cost components, while salary costs need not be mandatorily included in value where full ITC is not available.