Plain-language definition
The IP-based core for voice, video and messaging in 4G and 5G.
Technical definition
IMS uses SIP through P-CSCF, I-CSCF and S-CSCF with the HSS over Cx/Sh; SMS over IMS is carried as SIP MESSAGE and interworked with legacy domains by the IP-SM-GW.
Why it matters
VoLTE and VoNR subscribers need SMS continuity, which is the job of the IP-SM-GW and IMS-capable SMSC.
Last reviewed 2026-09-12 by the Guardivia QoS Engineering Team. Product facts on this page describe current capabilities; items marked “where supported”, “optional”, “integration” or “consultancy” are confirmed per deployment.