EN-DC
E-UTRAN-NR Dual Connectivity: an NSA architecture where the UE connects simultaneously to an LTE eNB (master node) and an NR gNB (secondary node) for increased throughput.
EN-DC is the dual connectivity that powers NSA 5G. The UE keeps a connection to an LTE eNB as the Master Node and simultaneously to an NR gNB as the Secondary Node, aggregating their throughput. The eNB owns the control plane and mobility; the gNB is added mainly for user-plane capacity. It's the most common dual-connectivity flavour because it's what almost every "5G" launch on a 4G core actually used.
A couple of specifics worth knowing. The NR node in EN-DC is formally an en-gNB — a gNB variant that connects to the EPC rather than the 5GC. Bearers can be split at the PDCP layer so a single flow uses both legs, or routed entirely down one. The "E-N" ordering matters: EN-DC is LTE-master, NR-secondary, which is the NSA case; NE-DC and NGEN-DC reverse or rebalance the roles for SA-anchored deployments. For a subscriber it means the phone shows 5G while LTE quietly does the control-plane heavy lifting underneath.
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