TN-NTN Integration — One Network, Ground and Sky

TN-NTN integration is about making terrestrial networks (ground towers) and non-terrestrial networks (satellites) work as one seamless system — so a device moves between them without the user noticing. This page explains what "integration" means in 3GPP, how continuity between ground and satellite works today, and where 6G is heading.

Status: TN-NTN handover is normative from Release 17; multi-connectivity between TN and NTN is a Release 19 work item. Native unified TN-NTN access is a 6G direction, not yet finalised.

What "integration" means in 3GPP

The important idea: NTN is not a separate network. It extends the same 5G NR air interface to satellites, inside the same operator network. The core network (the functions that handle registration, sessions, and data) is essentially unchanged — it doesn't care whether a device is reached by a ground tower or a satellite. All the integration work happens at the radio and device level. That is what lets ground and sky behave as a single system.

Moving between ground and satellite

Handover while connected. A device actively using the network can hand over between a terrestrial cell and a satellite cell, in both directions (ground-to-satellite and back). It can even hand over between satellites in different orbits. An honest limitation of the current releases: the device is not required to be connected to both at once during the switch, and the zero-interruption "make-before-break" technique (DAPS) is excluded for NTN — so there can be a brief break. A faster, RACH-less handover was added to reduce that gap.

Reselection while idle. When the device is idle, it chooses between terrestrial and satellite cells using standard priority and signal-strength rules. The SIB19 broadcast carries the NTN information it needs — satellite ephemeris, timing, service windows, and neighbour cells.

Service-link switch. For moving (non-geostationary) satellites, the network itself switches the device to the next satellite as one passes out of view, keeping the geographic cell stable.

Using both at once: TN-NTN multi-connectivity

Early releases did not let a device use terrestrial and satellite links simultaneously. Release 19 introduces TN-NTN multi-connectivity, where a device keeps connections to both a ground base station and a satellite base station at the same time — reusing the existing dual- connectivity framework. The benefits:

Reliability — if one access type loses coverage, the other carries on.
Capacity — both links can be used in parallel.
Continuity — a terrestrial anchor provides a stable control link while the satellite adds broad-area coverage.

The detailed normative text for this is being developed within the Release 19 timeframe.

Store-and-forward for patchy coverage

A satellite that is only overhead for a few minutes — and whose link to the ground gateway isn't always available at the same time as its link to the device — can't always provide a live end-to-end path. 3GPP defines store-and-forward for this: the device-to-satellite exchange and the satellite-to-ground exchange happen at different times rather than concurrently, a bit like how a text message doesn't need both ends online at once. It is defined for delay-tolerant IoT services and, from Release 18, extended toward NR. Inter-satellite links can complete the path when a direct one isn't available.

The 6G direction: native unified access

Today's integration adapts 5G NR with per-release additions. The 6G direction is to design for ground and sky from the start:

Regenerative satellites with on-board base stations (Release 19) turn satellites into real network nodes rather than relays.
Inter-satellite links form a space backbone that doesn't depend on a ground gateway always being in view.
The longer-term goal is a space-ground integrated network where whether a base station is on a tower or a satellite is just a deployment detail — with AI-assisted mobility predicting satellite passes and switching seamlessly.

These 6G aspects are study direction; the unified-access specifications are not yet complete.

Reference points (3GPP)

TS 38.300 §16.14 — NTN architecture, handover, and (Rel-19) multi-connectivity.
TS 38.331 — NTN RRC and SIB19 for cell reselection and mobility.
TS 22.261 — service requirements, including store-and-forward.
TS 23.401 — the IoT store-and-forward architecture.
TR 38.821 — the foundational NR-for-NTN study.

In short

TN-NTN integration makes ground and satellite access one system: hand over between them today, use both together from Release 19, and — looking to 6G — treat them as a single unified network designed for seamless coverage everywhere.