SMS Over IMS

Owned by Akin Laseinde (Deactivated)
Dec 18, 2024
1 min read

Introduction

SMS over SIP (Session Initiation Protocol) enables sending Short Message Service (SMS) messages over IP networks instead of traditional methods like SS7 or GSM. This is widely used in VoIP systems and modern telecom infrastructures to streamline messaging.

Key Flows

Registration

  • Devices register their SMS-over-IMS capability by including the +g.3gpp.smsip parameter in the Contact header of the SIP REGISTER request (RFC 3840).

Message Flows

  1. MO (Mobile Originated) SMS Flow:

  • Two dialogs:

    • Dialog 1: PCSCF → SCSCF

    • Dialog 2: SCSCF → IPSM-GW

  • Messages:

    • SMS-SUBMIT → SMS-SUBMIT REPORT

  1. MT (Mobile Terminated) SMS Flow:

  • Two dialogs:

    • Dialog 1: IPSM-GW → SCSCF

    • Dialog 2: SCSCF → PCSCF

  • Messages:

    • SMS-DELIVER → SMS-DELIVER REPORT

Correlation:

  • Use gsm_sms.tp_message_reference in Tshark for linking corresponding submit and report messages.

DIAMETER's Role in SMS Over SIP

Diameter protocol facilitates authentication, authorization, and charging during SMS flows within IMS.

  1. Before Message Exchange:

    • Cx Messages: User authentication and IMS registration.

      • MAR, SAR, LIR

    • Sh Messages: Retrieve subscriber profile (UDR/UDD).

  2. During Message Exchange:

    • Location Retrieval: SLg/S6c interfaces for user location.

    • Charging:

      • Gy Interface (Online Charging): Credit-Control Request/Answer (CCR/CCA).

      • Ro Interface (Offline Charging): Balance validation.

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