Skip to main content

OmniCall CSCF Operations Guide

Table of Contents​

  1. Overview
  2. Understanding IMS Architecture
  3. Call Session Flows
  4. CSCF Components
  5. Common Operations
  6. Troubleshooting
  7. Additional Documentation
  8. Glossary

Overview​

OmniCall CSCF is a comprehensive IMS (IP Multimedia Subsystem) solution that provides carrier-grade Call Session Control Functions for mobile and fixed-line service providers. Built on proven open-source technology and enhanced with enterprise-grade management capabilities, OmniCall CSCF delivers the core session control infrastructure required for VoLTE, VoWiFi, RCS, and traditional fixed-line VoIP services.

What is IMS?​

The IP Multimedia Subsystem (IMS) is the 3GPP-standardized architecture for delivering IP-based multimedia services. It provides:

  • Session control for voice, video, and messaging services
  • Quality of Service (QoS) management for real-time communications
  • Service convergence across mobile, fixed, and WiFi networks
  • Standards-based interoperability with other carriers and networks
  • Rich Communication Services (RCS) capabilities
  • Fixed-Mobile Convergence (FMC) for unified service delivery

OmniCall CSCF implements all core CSCF functions defined in 3GPP TS 23.228, providing a complete, production-ready IMS core network solution.

OmniCall CSCF Components​

OmniCall CSCF provides complete management of all CSCF network elements:

  • P-CSCF (Proxy-CSCF) - User-facing edge proxy and security anchor
  • E-CSCF (Emergency-CSCF) - Emergency services routing (integrated with P-CSCF)
  • I-CSCF (Interrogating-CSCF) - Network entry point and topology hiding
  • S-CSCF (Serving-CSCF) - Core session control, registration, and service triggering

Key Capabilities​

Network Functions:

  • Full 3GPP-compliant IMS session control
  • GSMA IR.92/IR.94 compliant - Works with any standards-compliant device, no custom carrier bundles required
  • VoLTE, VoWiFi, and RCS support
  • Fixed-line SIP service integration
  • Emergency services (E911/E112) support with location services
  • Topology hiding and network security
  • IPsec-based security associations
  • Diameter-based AAA and policy integration

Service Features:

  • Real-time call session management
  • Service triggering via Initial Filter Criteria (IFC)
  • Application Server (AS) integration via ISC interface
  • Charging integration (online and offline)
  • QoS policy enforcement via PCRF integration
  • Multi-tenancy support for MVNO scenarios

Management & Operations:

  • Real-time monitoring via web-based control panel
  • Prometheus metrics integration (see Metrics Reference)
  • RESTful API for automation
  • Distributed clustering for high availability
  • Live troubleshooting and diagnostics

Integrated Components:

  • OmniePDG: Evolved Packet Data Gateway for VoWiFi (IR.94 compliant)
  • OmniTAS: Telephony Application Server for supplementary services
  • OmniMessage: SMS/MMS Application Server (3GPP TS 24.341)

For detailed control panel usage, see Web UI Operations.

Understanding IMS Architecture​

IMS Network Architecture​

The OmniCall CSCF solution sits at the heart of the IMS architecture, providing the session control layer that connects user equipment to services and manages all call sessions.

How CSCFs Work Together​

The CSCF functions work as a coordinated system to handle IMS sessions:

  1. P-CSCF - First Point of Contact

    • User equipment (mobile, WiFi, or fixed-line devices) establish secure connections to P-CSCF
    • Provides IPsec security associations for mobile devices
    • Acts as the QoS policy enforcement point via PCRF integration
    • Handles NAT traversal and media anchoring
    • Routes emergency calls to E-CSCF functionality
    • Maintains user location information

  2. I-CSCF - Network Gateway & Load Balancer

    • Hides internal network topology from external networks
    • Queries HSS to select appropriate S-CSCF for users
    • Performs S-CSCF load balancing based on capabilities
    • Acts as the entry/exit point for roaming scenarios
    • Enforces Network Domain Security (NDS/TLS)

  3. S-CSCF - Core Session Controller

    • Performs user registration and authentication
    • Maintains session state for all active calls
    • Enforces routing policies and service logic
    • Triggers Application Servers based on IFC (Initial Filter Criteria)
    • Integrates with charging systems (online and offline)
    • Manages supplementary services

Integration with Supporting Systems​

OmniCall CSCF integrates with IMS support functions via standard 3GPP Diameter interfaces:

InterfaceFrom → ToPurpose3GPP Spec
CxI-CSCF/S-CSCF ↔ HSSUser authentication, profile retrieval, S-CSCF assignmentTS 29.228
DxI-CSCF ↔ SLFSubscription locator for multi-HSS environmentsTS 29.229
RxP-CSCF ↔ PCRFQoS policy authorization, media flow controlTS 29.214
RoS-CSCF → OCSOnline charging (credit control)TS 32.299
RfS-CSCF → CDFOffline charging (CDR generation)TS 32.299
ISCS-CSCF ↔ ASService triggering and application server invocationTS 23.228
ShAS ↔ HSSApplication server access to user dataTS 29.328

For Diameter peer management, see Diameter Operations.

Call Session Flows​

Understanding how CSCFs process different types of sessions is essential for operations and troubleshooting.

IMS Registration Flow​

When a device registers to the IMS network, the CSCFs coordinate to authenticate and authorize the user:

Key Points:

  • P-CSCF maintains IPsec security association with UE
  • I-CSCF queries HSS to find/assign S-CSCF
  • S-CSCF performs authentication and stores user profile
  • User's service profile (IFC) determines which Application Servers will be triggered

Mobile Originated Call Flow​

When a registered user initiates a call:

Key Points:

  • P-CSCF coordinates with PCRF for QoS bearer establishment
  • S-CSCF evaluates IFC to determine service triggering
  • OmniTAS provides telephony application services (call forwarding, screening, etc.)
  • OmniMessage handles SMS/MMS traffic when triggered by IFC
  • For monitoring active calls, see S-CSCF Dialog Management

Emergency Call Flow (E-CSCF)​

Emergency calls receive special handling to ensure connectivity even without full IMS registration:

Key Points:

  • E-CSCF functionality is integrated into P-CSCF
  • Works even for unregistered or roaming users
  • Includes callback number storage for emergency services
  • For emergency operations, see P-CSCF Emergency Services

SMS over IMS - Mobile Originated (3GPP TS 24.341)​

When a user sends an SMS via IMS, OmniMessage handles the message delivery:

Key Points:

  • SMS encoded in SIP MESSAGE method per 3GPP TS 24.341
  • Content-Type: application/vnd.3gpp.sms identifies SMS payload
  • S-CSCF IFC triggers OmniMessage for SMS traffic
  • OmniMessage interfaces with traditional SMSC infrastructure
  • Supports both GSM-7, UCS-2 character sets and concatenated messages

SMS over IMS - Mobile Terminated (3GPP TS 24.341)​

When an SMS arrives for an IMS-registered user, OmniMessage routes it via IMS:

Key Points:

  • SMSC forwards SMS to OmniMessage via traditional protocols (MAP/SMPP)
  • OmniMessage converts to SIP MESSAGE method
  • S-CSCF routes based on registered IMPU
  • Supports delivery reports and status notifications
  • Fallback to traditional SMS if user not IMS-registered

For SMS operations and monitoring, see S-CSCF IFC Management.

Roaming Scenarios​

OmniCall CSCF supports home-routed roaming as mandated by 3GPP/GSMA standards:

Home-Routed Roaming: When users roam to a visited network, all IMS sessions are routed back through the home network's S-CSCF. This ensures:

  • Consistent service experience regardless of location
  • Home network control over service triggering and charging
  • Simplified roaming agreements between operators
  • Compliance with GSMA PRD IR.92 and IR.94 standards

The visited network's I-CSCF queries the home HSS and routes registration/session requests to the home S-CSCF, which then invokes home network application servers (OmniTAS, OmniMessage, etc.).

For roaming configuration details, see I-CSCF Network Domain Security.

CSCF Components​

P-CSCF/E-CSCF - Edge Proxy and Security Anchor​

The Proxy-CSCF is the first IMS element that user equipment contacts. It serves as the security boundary and policy enforcement point.

Core Functions:

  • Security Association Management: Establishes and maintains IPsec tunnels with mobile devices for signaling and media protection
  • QoS Policy Enforcement: Coordinates with PCRF via Rx interface to authorize and enforce QoS bearers
  • NAT Traversal: Handles far-end NAT traversal for devices behind NAT/firewalls
  • Compression: SigComp support for bandwidth-constrained networks
  • Service Route: Maintains service route for subsequent requests

Emergency Services (E-CSCF):

  • Integrated emergency call routing without requiring full IMS registration
  • Location information handling for E911/E112
  • IMEI-to-callback number mapping for emergency callbacks
  • Integration with LRF (Location Retrieval Function)

Supported Access Types:

  • LTE/5G (VoLTE) via IPsec
  • WiFi (VoWiFi) via IPsec
  • Fixed broadband via SIP
  • Cable/DSL residential gateways

For detailed operations, see P-CSCF Documentation.

I-CSCF - Topology Hiding and Load Balancing​

The Interrogating-CSCF acts as the contact point within an operator's network for connections from other networks or from the same network.

Core Functions:

  • Topology Hiding: Shields internal network structure from external networks
  • S-CSCF Assignment: Queries HSS via Cx interface to assign S-CSCF to new users
  • S-CSCF Selection: Selects appropriate S-CSCF based on capabilities and load
  • Routing Proxy: Routes incoming requests to the assigned S-CSCF
  • Network Domain Security: Enforces NDS/TLS for inter-operator security

Key Features:

  • Multi-S-CSCF Support: Distributes users across multiple S-CSCF instances
  • Capability Matching: Matches user requirements to S-CSCF capabilities
  • Roaming Support: Handles both home-routed and local breakout scenarios
  • Subscription Locator: Dx interface support for multi-HSS environments

Use Cases:

  • Interconnection point for roaming partners
  • Load distribution across S-CSCF cluster
  • Geographic routing for disaster recovery
  • MVNO traffic segregation

For detailed operations, see I-CSCF Documentation.

S-CSCF - Core Session Controller​

The Serving-CSCF is the central component of the IMS network, providing session control and service intelligence.

Core Functions:

  • Registration: Authenticates users and maintains registration bindings
  • Session Control: Manages all call states (dialog establishment, modification, termination)
  • Service Triggering: Evaluates Initial Filter Criteria (IFC) to invoke Application Servers
  • Routing: Routes SIP requests based on service logic and user preferences
  • Charging Integration: Coordinates with online (OCS) and offline (CDF) charging systems

Service Triggering via IFC: The S-CSCF uses XML-based Initial Filter Criteria downloaded from HSS to determine when to route calls through Application Servers (such as OmniTAS for telephony services and OmniMessage for SMS/MMS):

  • Trigger Points: Match on SIP method, Request-URI, Session-Case (originating/terminating)
  • Priority-based: IFC processed in priority order
  • Service Chaining: Multiple AS can be invoked in sequence (e.g., OmniTAS → OmniMessage)
  • Default Handling: Configurable behavior when AS is unreachable

Supported Services:

  • Call forwarding (busy, no answer, unconditional)
  • Call barring (outgoing, incoming, roaming)
  • Call screening and filtering
  • Number translation and routing
  • Prepaid/postpaid charging
  • Usage tracking and quota enforcement
  • Supplementary services (call waiting, hold, transfer)

Scalability Features:

  • Distributed dialog storage
  • Stateful session handling
  • Database-backed user profiles
  • Horizontal scaling via I-CSCF distribution

For detailed operations, see S-CSCF Documentation.

Diameter Interface Management​

OmniCall CSCF provides comprehensive Diameter peer management across all CSCF components.

Supported Diameter Applications:

ApplicationInterfaceApp IDUsed ByPurpose
3GPP CxCx16777216I-CSCF, S-CSCFUser authentication, profile retrieval
3GPP DxDx16777216I-CSCFSubscription location in multi-HSS
3GPP RxRx16777236P-CSCFPolicy authorization, QoS control
3GPP RoRo4 (CC)S-CSCFOnline charging (credit control)
3GPP RfRf3 (Accounting)S-CSCFOffline charging (CDR)
3GPP ShSh16777217ASUser data access from AS

Diameter Capabilities:

  • Automatic peer discovery via DNS
  • Failover and redundancy support
  • Watchdog and connection management
  • Per-peer statistics and monitoring
  • Dynamic peer enable/disable

For Diameter operations and troubleshooting, see Diameter Management Guide.

Common Operations​

OmniCall CSCF provides comprehensive operational capabilities through its web-based control panel. This section covers common operational tasks and their significance.

Registration Management​

Understanding IMS Registrations:

IMS registration is a two-tier process:

  • P-CSCF Contact: User equipment establishes IPsec/SIP connection to P-CSCF
  • S-CSCF Registration: Full IMS registration with authentication via HSS

Key Registration Operations:

  • View active registrations across P-CSCF and S-CSCF
  • Query specific users by IMPU, IMSI, or IP address
  • Monitor registration state (authenticated, active, expired)
  • Force deregistration for troubleshooting or administrative purposes
  • Track registration expiry to identify re-registration issues

For detailed registration procedures, see:

Call Session Monitoring​

Dialog (Session) Management:

The S-CSCF maintains state for all active IMS sessions (calls). Operators can:

  • Monitor active dialogs including Call-ID, participants, and session state
  • View dialog details such as SDP (media parameters), route sets, and timers
  • Terminate dialogs for troubleshooting or emergency situations
  • Track session duration and detect long-running or stuck sessions

Session States:

  • Early: Call is ringing, not yet answered
  • Confirmed: Active call with media flowing
  • Terminated: Call ended normally

For call monitoring procedures, see S-CSCF Dialog Management.

Service Triggering and IFC Management​

Initial Filter Criteria (IFC) determines when and how the S-CSCF routes sessions to application servers like OmniTAS and OmniMessage.

IFC Operations:

  • Dump user's IFC to view configured service profile from HSS
  • Test IFC matching with simulated call scenarios
  • Verify AS routing to ensure proper service invocation
  • Debug service failures by examining trigger point evaluation

Example IFC Structure:

<InitialFilterCriteria>
  <Priority>10</Priority>
  <TriggerPoint>
    <SPT><Method>INVITE</Method></SPT>
    <SPT><SessionCase>0</SessionCase><!-- Originating --></SPT>
  </TriggerPoint>
  <ApplicationServer>
    <ServerName>sip:omnitas.ims.example.com</ServerName>
    <DefaultHandling>0</DefaultHandling><!-- Must invoke -->
  </ApplicationServer>
</InitialFilterCriteria>

For IFC testing and troubleshooting, see S-CSCF IFC Operations.

Diameter Peer Management​

Monitoring Diameter Connectivity:

OmniCall CSCF relies on Diameter interfaces for HSS, PCRF, and charging integration. Operators can:

  • Monitor peer status (I_Open = connected, Closed = disconnected)
  • View peer capabilities (supported Diameter applications)
  • Enable/disable peers for maintenance or failover testing
  • Track peer statistics (requests, failures, timeouts)

Critical Diameter Connections:

  • Cx to HSS (I-CSCF, S-CSCF): User authentication and profiles
  • Rx to PCRF (P-CSCF): QoS policy and bearer control
  • Ro to OCS (S-CSCF): Online charging and credit control

For Diameter troubleshooting, see Diameter Operations Guide.

Emergency Services Management​

E-CSCF Operations:

Emergency call handling requires special operational attention:

  • Monitor IMEI-to-callback mappings for emergency callbacks
  • Verify location information availability for E911/E112
  • Test emergency call routing without actual PSAP connection
  • Manage emergency registration for unprovisioned devices

Emergency services work even for:

  • Unregistered users
  • Users with no SIM/invalid credentials
  • Roaming users from other networks

For emergency operations, see P-CSCF Emergency Services.

Hash Table Management​

Shared Memory Data Structures:

CSCF nodes use in-memory hash tables for performance-critical data:

Hash TableCSCFPurposeTTL
imei_msisdnP-CSCFEmergency callback mapping24 hours
service_routesP-CSCFCached service routesRegistration expiry
authS-CSCFAuthentication vectorsChallenge timeout

Operations:

  • View table contents for troubleshooting
  • Delete specific entries to clear stale data
  • Flush entire tables for emergency recovery (use with caution)

For detailed UI operations, see the Web UI Operations Guide.

Troubleshooting​

This section covers common operational issues and their resolution strategies.

Registration Failures​

Symptoms: Users unable to register to IMS network, registration timeouts

Common Root Causes:

  1. HSS Connectivity Issues

    • Check Diameter Cx peer status on I-CSCF and S-CSCF
    • Verify HSS is reachable and responding to UAR/MAR requests
    • Check for Diameter routing issues

  2. Authentication Failures

    • Verify user credentials provisioned in HSS
    • Check authentication vector generation (MAR/MAA)
    • Verify AKA algorithm compatibility (Milenage)

  3. P-CSCF Connectivity

    • Verify IPsec SA establishment for mobile devices
    • Check NAT traversal for devices behind NAT
    • Verify P-CSCF discovery (DNS, DHCP, or static configuration)

  4. S-CSCF Assignment

    • Check I-CSCF S-CSCF selection logic
    • Verify S-CSCF capabilities match user requirements
    • Check S-CSCF capacity (registration limits)

For detailed troubleshooting, see component-specific guides:

Call Setup Failures​

Symptoms: Calls fail to establish, receive 4xx/5xx SIP errors

Common Root Causes:

  1. User Not Registered

    • Verify both originating and terminating users are IMS-registered
    • Check registration status via S-CSCF

  2. IFC/Service Triggering Issues

    • Verify IFC downloaded from HSS (check SAR/SAA)
    • Test IFC matching for call scenario
    • Check OmniTAS/OmniMessage availability if triggered

  3. QoS/PCRF Issues

    • Verify Rx Diameter peer status on P-CSCF
    • Check PCRF QoS policy authorization
    • Verify bearer resources available in access network

  4. Routing Failures

    • Verify destination routing (ENUM, number translation)
    • Check interconnect/MGCF configuration for PSTN calls
    • Verify roaming routing for off-net calls

Diameter Connectivity Issues​

Symptoms: Diameter peer shows "Closed" state, operations timing out

Diagnosis Steps:

  1. Check Peer Status: Use control panel to view Diameter peer state
  2. Verify Network Connectivity: Test IP reachability to Diameter peer (port 3868)
  3. Check Capabilities: Verify Application IDs match between peers
  4. Review Watchdog: Check Diameter watchdog (DWR/DWA) exchanges

Critical Diameter Interfaces:

InterfaceImpact if DownRecovery Priority
Cx (HSS)No new registrations, no IFC updatesCritical - immediate
Rx (PCRF)No QoS for new callsHigh - within minutes
Ro (OCS)No prepaid charging, service may continueHigh - depends on policy

For Diameter troubleshooting, see Diameter Operations Guide.

SMS Delivery Issues​

Symptoms: SMS not delivered via IMS, fallback to legacy SMSC

Common Root Causes:

  1. OmniMessage Not Triggered

    • Verify IFC configured to trigger OmniMessage for MESSAGE requests
    • Check IFC priority (should be higher than other AS)
    • Test IFC matching with simulated SMS

  2. SMSC Integration

    • Verify OmniMessage to SMSC connectivity (MAP/SMPP)
    • Check message format conversion (SIP MESSAGE ↔ SMS PDU)
    • Verify subscriber routing in SMSC

  3. Content Type Issues

    • Verify Content-Type: application/vnd.3gpp.sms in SIP MESSAGE
    • Check character set encoding (GSM-7, UCS-2)

For SMS troubleshooting, see S-CSCF IFC Management.

Emergency Call Issues​

Symptoms: Emergency calls not routing to PSAP, location not included

Common Root Causes:

  1. E-CSCF Detection

    • Verify emergency URN detection (urn:service:sos)
    • Check emergency routing rules on P-CSCF
    • Verify LRF connectivity

  2. Location Information

    • Check location header in SIP INVITE
    • Verify IMEI-to-callback mapping for callbacks
    • Test location retrieval from LRF

  3. PSAP Routing

    • Verify PSAP routing table configuration
    • Check ESQK (Emergency Service Query Key) generation
    • Verify trunk/interconnect to PSAP

For emergency services operations, see P-CSCF Emergency Services.

Performance Degradation​

Symptoms: Slow call setup, registration delays, high latency

Diagnosis:

  1. Monitor Prometheus Metrics: Check CSCF performance metrics (see Metrics Reference for complete metric definitions)
  2. Database Performance: Verify S-CSCF database query times
  3. Network Latency: Check latency between CSCF nodes
  4. Resource Utilization: Monitor CPU, memory, and network on CSCF servers

Scalability Considerations:

  • P-CSCF: ~50,000 IPsec SAs per instance (VoLTE); 100,000+ via OmniePDG (VoWiFi)
  • I-CSCF: Stateless, scales horizontally (1,000-5,000 registrations/sec per instance)
  • S-CSCF: 100,000-500,000 registrations per instance; 20,000-100,000 concurrent dialogs

For detailed capacity planning and deployment sizing, see the Capacity and Dimensioning Guide.

For performance monitoring and metrics, see the Web UI Operations Guide.

Additional Documentation​

Component-Specific Operations Guides​

For detailed operations and troubleshooting for each CSCF component:

Regulatory Compliance​

3GPP Standards Reference​

OmniCall CSCF implements the following 3GPP specifications:

SpecificationTitleRelevance
TS 23.228IP Multimedia Subsystem (IMS) - Stage 2Core IMS architecture
TS 24.229IP multimedia call control protocol (SIP)IMS SIP profile
TS 29.228Cx and Dx interfaces (CSCF-HSS)User data and authentication
TS 29.214Rx interface (P-CSCF-PCRF)QoS policy control
TS 32.299Charging - Diameter applicationsOnline/offline charging
TS 24.341SMS over IP networksSMS over IMS
TS 23.167Emergency servicesE-CSCF and emergency calls

GSMA Standards Compliance​

OmniCall CSCF is fully compliant with GSMA IMS profiles, ensuring interoperability with off-the-shelf devices:

IR.92 - IMS Profile for Voice and SMS (VoLTE)​

GSMA PRD IR.92 defines the mandatory IMS profile for VoLTE services, ensuring that commercial devices work seamlessly without carrier-specific configuration or custom device bundles.

Key IR.92 Benefits for OmniCall CSCF:

✓ Open Market Device Support: Any IR.92-compliant smartphone works immediately—no custom carrier bundles, proprietary APNs, or special provisioning required

✓ Standardized SIP Profile: Devices use standard SIP headers, authentication, and registration flows as defined in 3GPP TS 24.229

✓ Codec Interoperability: Mandatory codec support (AMR-WB for HD Voice) ensures consistent voice quality across all devices

✓ SMS over IMS: Integration with OmniMessage provides standards-based SMS delivery (TS 24.341) to any IR.92 device

✓ Emergency Services: E.164 emergency number handling (911, 112, etc.) works on all compliant devices without special configuration

✓ Roaming Consistency: Home-routed roaming ensures users get the same VoLTE experience when visiting other IR.92-compliant networks

What This Means: Operators can launch VoLTE services immediately with existing consumer devices (iPhone, Samsung, Google Pixel, etc.) without waiting for custom device certification or carrier bundle updates.

IR.94 - IMS Profile for Voice, Video and SMS (VoWiFi)​

GSMA PRD IR.94 extends IR.92 to include Voice over WiFi, enabling VoLTE services over untrusted WiFi networks.

VoWiFi Architecture with OmniCall:

VoWiFi Components:

  • OmniePDG: Evolved Packet Data Gateway - Provides IPsec tunnel termination for untrusted WiFi access
  • OmniCall P-CSCF: Handles VoWiFi registrations identically to VoLTE (same service routes, same IFC triggering)
  • Seamless Handover: Devices can move between LTE and WiFi without call interruption

IR.94 Benefits:

  • Same IR.92 benefits apply to VoWiFi
  • Devices automatically discover ePDG via DNS (no manual configuration)
  • Single IMS registration covers both VoLTE and VoWiFi
  • Indoor coverage extension without femtocells or DAS

For ePDG operations and VoWiFi troubleshooting, see OmniePDG Documentation.

Other GSMA Standards​

  • IR.51 - GSMA Roaming Database Structure
  • IR.88 - LTE Roaming Guidelines
  • AA.80 - IMS/RCS Device Configuration and Supporting Services

Product Differentiation​

Why Choose OmniCall CSCF?

✓ Plug-and-Play Device Support: GSMA IR.92/IR.94 compliant - works with off-the-shelf iPhones, Android phones, and fixed-line devices without custom carrier bundles or device certification delays

✓ Complete IMS Solution: All CSCF components (P/I/S/E) plus OmniePDG for VoWiFi in a unified platform

✓ Fixed-Mobile Convergence: Unified IMS core for mobile (VoLTE/VoWiFi), fixed broadband, and cable telephony services

✓ Zero Touch Provisioning: Standards-based device discovery (DNS, DHCP) means users can swap SIM cards between devices without IT support

✓ Enterprise Management: Web-based control panel with real-time monitoring, diagnostics, and troubleshooting

✓ Carrier-Grade Scalability: Horizontal scaling to support millions of subscribers with sub-second call setup times

✓ Application Server Ecosystem: Seamless integration with OmniTAS (telephony services) and OmniMessage (SMS/MMS)

✓ Emergency Services: Built-in E-CSCF with E911/E112 support, location services, and callback handling

✓ Interoperability First: Full 3GPP and GSMA compliance ensures roaming agreements and interconnection work out-of-the-box

✓ Production Proven: Deployed in tier-1, tier-2, and MVNO networks worldwide serving millions of subscribers

Glossary​

IMS Architecture Terms​

  • 3GPP: 3rd Generation Partnership Project - Standards body for mobile telecommunications
  • AKA: Authentication and Key Agreement - Security mechanism for IMS
  • AoR: Address of Record - SIP identity (e.g., sip:user@domain.com)
  • CSCF: Call Session Control Function - IMS session control entity
  • DAS: Distributed Antenna System - Indoor coverage solution
  • E-CSCF: Emergency CSCF - Emergency call routing function
  • ePDG: Evolved Packet Data Gateway - IPsec tunnel endpoint for untrusted WiFi access
  • ENUM: E.164 Number Mapping - DNS-based number translation
  • ESQK: Emergency Service Query Key - Emergency call identifier
  • FMC: Fixed-Mobile Convergence - Unified services across access types
  • GSMA: GSM Association - Mobile industry standards organization
  • HD Voice: High Definition Voice - Wideband audio using AMR-WB codec
  • HSS: Home Subscriber Server - Subscriber database and authentication
  • I-CSCF: Interrogating CSCF - Network entry point and topology hiding
  • IFC: Initial Filter Criteria - XML-based service triggering rules
  • IMS: IP Multimedia Subsystem - 3GPP architecture for IP-based services
  • IMPU: IP Multimedia Public Identity - User's public identity (SIP URI or tel URI)
  • IMSI: International Mobile Subscriber Identity - Subscriber identifier
  • IR.92: GSMA IMS Profile for Voice and SMS - VoLTE interoperability standard
  • IR.94: GSMA IMS Profile for Conversational Video - VoWiFi interoperability standard
  • ISC: IMS Service Control - Interface between S-CSCF and Application Servers
  • LRF: Location Retrieval Function - Emergency location services
  • MGCF: Media Gateway Control Function - PSTN interconnection
  • MVNO: Mobile Virtual Network Operator - Operator without own radio infrastructure
  • NDS: Network Domain Security - Inter-operator security (TLS/IPsec)
  • P-CSCF: Proxy CSCF - Edge proxy and first point of contact
  • PSAP: Public Safety Answering Point - Emergency services call center
  • RCS: Rich Communication Services - Enhanced messaging services
  • S-CSCF: Serving CSCF - Core session control and registration
  • SPT: Service Point Trigger - Matching condition in IFC (Method, Request-URI, etc.)
  • SWu: 3GPP interface between UE and ePDG (IPsec/IKEv2)
  • UE: User Equipment - End-user device (phone, tablet, fixed terminal)
  • VoLTE: Voice over LTE - Voice services via LTE data network
  • VoWiFi: Voice over WiFi - Voice services via untrusted WiFi networks

Diameter Protocol Terms​

  • AAA: Authentication, Authorization, Accounting
  • AVP: Attribute-Value Pair - Diameter message data element
  • CCR/CCA: Credit-Control-Request/Answer - Online charging messages
  • CDF: Charging Data Function - Offline charging collector
  • Cx: Diameter interface between I-CSCF/S-CSCF and HSS
  • Diameter: AAA protocol used in IMS (evolution of RADIUS)
  • Dx: Diameter interface between I-CSCF and SLF (subscription locator)
  • DWR/DWA: Device-Watchdog-Request/Answer - Peer health check
  • MAR/MAA: Multimedia-Auth-Request/Answer - Authentication vector request
  • OCS: Online Charging System - Real-time charging and credit control
  • PCRF: Policy and Charging Rules Function - QoS policy server
  • Rf: Diameter interface for offline charging (accounting)
  • Ro: Diameter interface for online charging (credit control)
  • Rx: Diameter interface between P-CSCF and PCRF (QoS authorization)
  • SAR/SAA: Server-Assignment-Request/Answer - User profile download
  • Sh: Diameter interface between AS and HSS (user data access)
  • SLF: Subscription Locator Function - HSS location in multi-HSS environment
  • UAR/UAA: User-Authorization-Request/Answer - S-CSCF selection

OmniCall Product Terms​

  • OmniCall CSCF: Complete IMS CSCF solution (this product)
  • OmniePDG: Evolved Packet Data Gateway - IPsec tunnel termination for VoWiFi (IR.94 compliant)
  • OmniTAS: Telephony Application Server - Provides supplementary voice services
  • OmniMessage: Messaging Application Server - SMS/MMS over IMS (TS 24.341)

SIP Protocol Terms​

  • Dialog: SIP session state between two endpoints
  • INVITE: SIP method for session establishment (calls)
  • MESSAGE: SIP method for instant messaging (including SMS over IMS)
  • REGISTER: SIP method for user registration
  • SDP: Session Description Protocol - Media parameters (codecs, ports)
  • SIP: Session Initiation Protocol - Signaling protocol for IMS