MTSI (Multimedia Telephony Service for IMS)

Also known as: Multimedia Telephony Service for IMS

MTSI is the 3GPP-defined telephony service profile that VoLTE and VoNR implement on top of the IMS. It specifies the mandatory and optional media codecs, SIP procedures, supplementary services, and end-to-end QoS behaviour a conforming client and network must support. GSMA profiles IR.92 (VoLTE) and IR.94 (video / ViLTE) are MTSI-based. MTSI conformance is a prerequisite for interoperable, security-hardened voice service.

Categories: Radio Access NetworkSignalingProtocols and Standards

MTSI in context

The radio access network is where mobile devices attach to the operator's infrastructure. Attacks in this layer include IMSI catching, rogue base stations and downgrade attacks; defenses rest on mutual authentication, integrity-protected signaling and Open RAN supply-chain hygiene.

Signaling protocols carry the control-plane messages that set up calls, register subscribers and route SMS. SS7, Diameter, GTP-C and SIP are the four dominant families, and interconnect exposure of any of them is treated by GSMA as top-tier telecom risk.

To place MTSI in the wider telecom-security picture, review XnAP, 1G, 5G SA, 5GNR, 6G and ADSL — each entry cross-references back to this page so you can walk the topic in either direction.

Related terms

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