Dokodemo IMS technical specifications
Dokodemo IMS follows established industry standards including 3GPP TS 23.228. This page summarizes the key technical aspects.
Architecture
The IMS architecture is split into application, control and transport layers, with standardized interfaces for scalability, flexibility and extensibility. It is access-independent and supports IP connectivity access networks (IP-CAN) such as GPRS, EPS, 5GS and untrusted WLAN. The framework separates bearer, session control and service levels, and includes mechanisms for NAT traversal, border control and optimal media routing (OMR).
Key functional entities
| Entity | Role | Location | Notes |
|---|---|---|---|
| P-CSCF | Entry point for UE signaling, SIP forwarding, NAT traversal, QoS authorization, emergency and priority sessions. | Visited or home | IPv4/IPv6 interworking, extended for WebRTC. |
| I-CSCF | Handles incoming SIP requests and queries the HSS for routing. | Home | Supports transit routing and SBI integration. |
| S-CSCF | Central session control, registration and service invocation. | Home | Keeps session state, supports GRUU assignment. |
| AS | Hosts service logic, supports PSI for conferencing and messaging. | Home or third party | Acts as SIP B2BUA, enforces data-off exempt services. |
| HSS | Stores subscription data, authentication and location. | Home | Interfaces with CSCFs and ASs, supports SBI for 5GS. |
| BGCF | Routes sessions to the PSTN/CS domain. | Home | Selects the MGCF based on protocol information. |
| MGCF | Interfaces with the PSTN and controls the MGW for media. | Home | Converts SIP to ISUP/BICC. |
| MRFC / MRFP | Controls media resources, handles mixing and announcements. | Home | Supports transcoding and floor control. |
| IMS-AGW | Manages media flows, NAT traversal and resource allocation. | Visited or home | Extended for WebRTC with DTLS-SRTP. |
| TrGW | Media forwarding and transcoding. | Home or border | Controlled by the IBCF, can be bypassed with OMR. |
| IBCF | Border control and topology hiding. | Border | Supports II-NNI. |
| ePDG | Secure access from untrusted WLAN. | Visited | Interfaces with the P-GW, also for 5GS. |
| WWSF | Serves the UI and JavaScript for WebRTC access. | Home or third party | Supports HTTPS access. |
| WAF | Issues authorization tokens for WebRTC. | Home | Supports web authentication. |
Reference points and interfaces
| Interface | Purpose | Protocol | Notes |
|---|---|---|---|
| Gm | Registration and session control from UE to P-CSCF. | SIP (TCP/UDP) | Extended for WebRTC (W2). |
| Mw | SIP signaling between CSCFs. | SIP | Intra-IMS signaling. |
| Cx | Profile and authentication from CSCF to HSS. | Diameter | Mapped to SBI for 5GS. |
| Sh | Data management from AS to HSS. | Diameter | Supports transparent data. |
| ISC | Service control from S-CSCF to AS. | SIP | B2BUA for media. |
| Dx / Dh | HSS resolution from CSCF/AS to SLF. | Diameter | For multi-HSS setups. |
| Iq | NAT control from P-CSCF to IMS access gateway. | Implementation-specific | Supports IPv4/IPv6. |
| Ix | Media control from IBCF to TrGW. | H.248 | For II-NNI. |
| Mx | Border control from CSCF to IBCF. | SIP | Topology hiding. |
| Mm | From CSCF/IMS-ALG to external IP networks. | SIP | Interworking entry and exit. |
| Ici | SIP between IMS networks via IBCF. | SIP | II-NNI signaling. |
| Izi | Media between IMS networks via TrGW. | RTP/RTCP | Media transport. |
| Mg | SIP for PSTN from MGCF to CSCF. | SIP | ISUP/BICC conversion. |
| Mi | PSTN routing from CSCF to BGCF. | SIP | Breakout routing. |
| Mj | Session routing from BGCF to MGCF. | SIP | PSTN selection. |
| Mk | Transit from BGCF/IMS-ALG to BGCF. | SIP | Complex routing. |
| Mr / Mr′ | Media control from MRFC to MRFP. | SIP / H.248 | Conferencing. |
| Cr | Media resource requests from AS to MRFC. | SIP | AS-initiated control. |
| Mp | Bearer control from MRFC to MRFP. | H.248 | Media mixing. |
| Rx / N5 | QoS from P-CSCF to PCF/PCRF. | Diameter / SBI | Resource reservation. |
| Ut | Service configuration from UE to AS. | HTTP (XCAP) | Group management and settings. |
| W1 | UI download from UE to WWSF. | HTTPS | WebRTC access. |
| W2 | SIP over WebSocket from UE to eP-CSCF. | SIP over WebSocket | Secure signaling. |
| W3 | Media from UE to eIMS-AGW. | RTP/RTCP, DTLS-SRTP | NAT traversal. |
| W4 | Tokens from WWSF to WAF. | Implementation-specific | Authorization. |
| W5 | Signaling from WAF to eP-CSCF. | Implementation-specific | WebRTC security. |
| S2b | WLAN access from ePDG to P-GW. | GTP-C / GTP-U | Non-3GPP access integration. |
| N6 | Media on the 5GS user plane. | IP | QoS flows. |
Protocols
- Signaling
- SIP (RFC 3261) with extensions for GRUU, PSI, MPS and NAT traversal (Outbound RFC 5626, ICE RFC 5245). Diameter for the Cx and Sh interfaces.
- Media
- RTP/RTCP for transport, SRTP for protection, DTLS for key exchange, SCTP for data channels (MSRP, BFCP, T.140).
- Control and interworking
- SDP for media negotiation, H.248 for MGW/MRFP control, SS7/MGCP for PSTN interworking.
- DTMF
- In-band signaling with tone generation and detection in the MGW.
- QoS
- Policy and charging control (PCC) over Rx/N5 for resource reservation.
Capabilities
- Multimedia services: voice (VoLTE/VoNR), video (ViLTE), text messaging, conferencing and collaboration.
- Session control: registration, setup, hold and resume, release, immediate and session-based messaging.
- WebRTC support: secure access through eP-CSCF, eIMS-AGW and WWSF/WAF.
- Emergency sessions: priority handling and location retrieval.
- Roaming: home routing, local breakout and transit.
- Interworking: PSTN through MGCF/MGW, external IMS and SIP networks through IBCF/TrGW.
- Policy and AAA: policy-based QoS, authentication, authorization and accounting.
- Cloud-native services: RCS, VoWiFi, VoBB and more.
Session control procedures
| Procedure | Description | Notes |
|---|---|---|
| Registration | UE sends REGISTER to the P-CSCF, forwarded to the I/S-CSCF with an HSS query. Supports implicit registration and GRUU. | Multiple registrations, re-registration and deregistration. |
| Session setup | INVITE/SDP for originating and terminating calls, QoS authorization, OMR for routing. | Supports MO/MT, PSTN and AS scenarios. |
| Hold and resume | re-INVITE with updated SDP to hold and resume media. | Mobile-to-mobile and PSTN, NAT handling. |
| Session release | BYE from UE or network, with resources released. | Handles loss of coverage. |
| Immediate messaging | Messages to registered and unregistered identities, with AS filtering. | Multiple recipients through PSI. |
| Session-based messaging | SDP negotiation for messaging sessions, MSRP transport. | Chat groups and policy enforcement. |
| Conferencing and chat | MRFC/MRFP for media control and message distribution. | Codec transcoding. |
| Emergency sessions | Priority at the P-CSCF, QoS through PCRF/PCF. | Regulatory location support. |
| Mid-session signaling | Codec changes and media adjustments by re-INVITE. | Policy and QoS continuity. |
Security
- Authentication
- IMS-AKA through the HSS, web authentication for WebRTC.
- NAT traversal
- IMS-ALG, ICE, STUN/TURN and Outbound.
- Protection
- TLS and IPsec for signaling, overload control, policy enforcement at the P-CSCF and S-CSCF.
- Network domain security
- Compliant with TS 33.210.
Integration with other networks
| Network | Integration | Key entities and procedures |
|---|---|---|
| PSTN | Routing through BGCF/MGCF, SIP to ISUP/BICC conversion, media transcoding and DTMF. | Interworking through MGCF/MGW, SS7/MGCP. |
| Internet and external IMS | Border control through IBCF/TrGW, II-NNI (Ici/Izi). | SIP/RTP for signaling and media, topology hiding. |
| 5G | Integration with the 5GC (AMF, SMF, UPF, PCF) and SBI over N5/N70/N71/Nhss. | QoS flows over N6, roaming support. |
Standards compliance
- 3GPP
- Releases 5 to 18, for example TS 23.228 (architecture), TS 24.229 (SIP/SDP), TS 29.228 (Cx/Dx) and TS 29.162 (Ix).
- IETF RFCs
- SIP (3261), SDP, RTP/RTCP, Diameter, H.248, ICE (5245), Outbound (5626), STUN (5389).
Deployment options
- Virtualized
- NFV on VMware or KVM.
- Containerized
- Cloud-native scaling with Kubernetes.
- Bare metal
- For high-performance on-premises setups.
- Supported networks
- 4G/5G mobile, Wi-Fi, fixed and MSO networks. Reusable components reduce CAPEX and OPEX.
Performance and benefits
- Scalability
- From tens to millions of users with horizontal NFV scaling.
- Latency
- VoLTE/VoNR call setup under 50 ms, with URLLC support.
- Security
- TLS/IPsec, AKA authentication and lawful interception.
- Benefits
- Vendor independence, service interconnection, guaranteed QoS, and migration from legacy to all-IP networks.
Planning IMS for your network?
Our engineers can help with integration into 3GPP networks, customization for your industry, or a VoLTE/VoNR demo.