For buyers contracting authority
Pick 72318000 when the contract's main purpose is carrying data across a network: leased lines, data circuits, MPLS connectivity between sites, or a managed link that moves a feed from a source to its consumers. The test is whether the deliverable is the transport itself rather than what happens at either end of it.
Two sibling boundaries trip contracting authorities. Data storage services (72317000) is where the data sits at rest, not where it travels; Data network management and support services (72315000) is for running and supporting the network, not for the transmission capacity itself. Where a single contract bundles a circuit with the management of it, tag the primary CPV code by whichever dominates the statement of work.
The other boundary is upward, into telecommunications. When the procurement is a general telecoms connectivity buy rather than a data-processing service, 64200000 (Telecommunications services) is often the cleaner fit. Reserve 72318000 for transmission that sits inside a data-processing remit.