IMS Cloud Core

Cloud-native simulation of 3GPP IMS (IP Multimedia Subsystem) core network functions. Each IMS network element runs as an independent Spring Boot microservice, communicating via REST APIs that simulate SIP and Diameter interfaces.

IMS Architecture

                    ┌─────────────────────┐
                    │   Telephony AS      │
                    │   (Call Services)    │
                    └─────────┬───────────┘
                              │ ISC (SIP)
    ┌──────────┐    ┌─────────┴───────────┐    ┌──────────┐
    │          │ Gm │                     │ Cx │          │
    │  P-CSCF  ├────┤      S-CSCF        ├────┤   HSS    │
    │          │    │                     │    │          │
    └──────────┘    └─────────┬───────────┘    └────┬─────┘
                              │                     │ Dx
                    ┌─────────┴───────────┐    ┌────┴─────┐
                    │      I-CSCF         ├────┤   SLF    │
                    │                     │    │          │
                    └─────────────────────┘    └──────────┘

    Interfaces:
    Gm  — UE ↔ P-CSCF (SIP)
    Mw  — CSCF ↔ CSCF (SIP)
    Cx  — S-CSCF/I-CSCF ↔ HSS (Diameter)
    Dx  — I-CSCF ↔ SLF (Diameter)
    ISC — S-CSCF ↔ AS (SIP)

Microservices

Service	Port	3GPP Function	Description
P-CSCF	8083	Proxy-CSCF	First point of contact, SIP proxy, IPSec
I-CSCF	8084	Interrogating-CSCF	Entry point, S-CSCF selection
S-CSCF	8082	Serving-CSCF	Core SIP server, registration, session control
HSS	8081	Home Subscriber Server	User database, auth vectors, profiles
Telephony AS	8085	Application Server	Call forwarding, barring, supplementary services

IMS Registration Flow

  UE            P-CSCF         I-CSCF         S-CSCF          HSS
   │               │              │              │              │
   │──REGISTER────>│              │              │              │
   │               │──REGISTER───>│              │              │
   │               │              │──Cx:UAR─────>│              │
   │               │              │<─Cx:UAA──────│              │
   │               │              │──REGISTER───>│              │
   │               │              │              │──Cx:MAR─────>│
   │               │              │              │<─Cx:MAA──────│
   │               │              │              │  (Auth Vector)│
   │<──401─────────│<─────────────│<─────────────│              │
   │               │              │              │              │
   │──REGISTER────>│──REGISTER───>│──REGISTER───>│              │
   │  (credentials)│              │              │──Cx:SAR─────>│
   │               │              │              │<─Cx:SAA──────│
   │<──200 OK──────│<─────────────│<─────────────│              │
   │               │              │              │              │

Supplementary Services (Telephony AS)

• Call Forwarding: CFU (Unconditional), CFB (Busy), CFNR (No Reply)
• Call Barring: BAOC (All Outgoing), BAIC (All Incoming), BOIC (International)
• Identity Services: OIP/OIR, TIP/TIR

Quick Start

docker-compose up -d

Technology Stack

• Java 17, Spring Boot 3.2, Spring Cloud
• Docker with multi-service Compose
• Kubernetes with Helm charts
• PostgreSQL for HSS subscriber data
• 3GPP TS 23.228 (IMS Architecture)
• 3GPP TS 29.228/229 (Cx/Dx Interface)

License

MIT License — see LICENSE for details.