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Glossary term · Core Network

S8HR

S8 Home Routing

Core Network →

S8HR is the EPC/VoLTE roaming architecture that routes IMS traffic through the home PLMN over the S8 path; N9HR is the corresponding home-routed arrangement for 5GC/VoNR.

Introduced
Rel-14
Where
Core Network › Evolved Packet Core
Specifications
5 specs
S8HR Description Purpose What changed Neighbours Detected Changes Specifications

Description

S8 Home Routing (S8HR) is a 4G/EPC roaming architecture for Voice over LTE. It uses the S8 reference point between the visited network's Serving Gateway (SGW) and the home network's Packet Data Network Gateway (PGW). The PGW remains in the Home Public Land Mobile Network (HPLMN), so the user plane is routed home rather than broken out locally in the visited network.

For VoLTE, IMS signalling and media are carried over GTP bearers through the EPC home-routed path. The S8HR name refers to this EPC S8 user-plane routing; it is not an interface name for the 5G Core. The architecture is distinct from Local Breakout, where traffic exits through the visited network.

5G Core roaming uses different functions and reference points. Its comparable home-routed voice arrangement is described as N9 Home Routing (N9HR), using the 5GC PDU Session, QoS flows and SMF/UPF functions. S8HR and N9HR therefore describe related goals in different core architectures.

Purpose & Motivation

S8HR was studied and standardised for VoLTE roaming in the EPC era, with the 3GPP work recorded in TR 23.749 and related Rel-14 specifications. It gives the home operator control of IMS service treatment, charging and policy while a subscriber is attached to a visited LTE network.

The introduction of 5GC did not rename S8HR as a 5G concept. 5GC separates control and user plane functions differently and uses N9/N16 reference points; the corresponding home-routed voice architecture is N9HR. Keeping these names separate prevents an EPC procedure from being attributed to 5GC.

What changed in its specifications

The latest release-to-release comparison of specifications that define S8HR. Each summary describes the whole specification, not only this term.

TS 29.244Rel-18 → Rel-19

Rel-19 adds MPQUIC-based steering for multi-access PDU sessions and SMF restoration with alternative-SMF handling. It also adds RTP header handling rules, Media over QUIC payload handling, and N6 delay measurement between UPF and endpoints.

Full comparison in TS 29.244 →
TS 33.107Rel-18 → Rel-19

Rel-19 brings only minor changes to TS 33.107: 0 clauses changed, with no change attributed to a release feature.

Full comparison in TS 33.107 →

Release Timeline

Detected Changes Across Releases

from 3GPP Change Requests

Specific changes extracted from the „Change history“ tables of 3GPP specifications (4 CRs across 2 releases). Complements the general historical overview above with the evidence-based evolution of this function.

Rel-15 3 changes
  • Reporting Media Bearer information for S8HR TS 33.107CR0300
  • S8HR LI: Location reporting corrections in Annex J TS 33.107CR0301
  • Critical fix for location reporting with S8HR LI (stage 2 text) TS 33.107CR0294
Rel-16 1 change
  • LI in VPLMN with home routed roaming scenario – S8HR LI TS 33.127CR0058

Defining Specifications

3GPP specifications that define or reference S8HR, with the latest known release. Sourced from the 3GPP document catalog — see methodology.

SpecificationTitleRelease
TR 23.749 ve00 Study on S8 Home Routing for VoLTE Rel-14 read
TS 29.244 vk10 PFCP for Control and User Plane Separation Rel-20 read
TS 33.107 vj00 Lawful Interception Architecture & Functions Rel-19 read
TS 33.127 vj80 Lawful Interception Architecture Rel-19 read
TS 33.827 ve00 LI for S8 Home Routed VoLTE Roaming Rel-14 read