Telecom Call Flows

A comprehensive open-source knowledge base of LTE, EPC, IMS, VoLTE, VoNR, and 5G Core signaling procedures.

Built and maintained by Muhammad Usman to document practical mobile core network procedures and troubleshooting based on industry standards.

Mission

To build a comprehensive, standards-based telecom knowledge repository that helps engineers understand signaling procedures across LTE, EPC, IMS, VoLTE, VoNR, and 5G Core networks through practical documentation and real-world troubleshooting.

This repository provides practical call flows, troubleshooting guides, protocol explanations, and references to relevant 3GPP standards for telecom engineers and mobile core network professionals.

Overview

This repository is a structured knowledge base covering telecommunications signaling procedures, protocol interactions, and call flows across LTE, EPC, IMS, VoLTE, VoNR, and 5G Core networks.

The goal is to provide practical learning resources, troubleshooting guidance, and technical references for telecom engineers, students, and professionals working with mobile core networks.

All content is written in an educational format and is based on publicly available standards and industry best practices.

Why this Repository?

Understanding telecom signaling requires more than reading standards.

This repository explains complex procedures in a practical and structured way using:

• Step-by-step signaling procedures

• Call flow diagrams

• Architecture illustrations

• Troubleshooting scenarios

• Technical explanations

• References to public standards

  Target Audience

This repository is intended for:

• Telecom Engineers
• PS Core Engineers
• IMS Engineers
• 5G Core Engineers
• Cloud Core Engineers
• Students
• Researchers

Technologies Covered

• LTE
• EPC
• IMS
• VoLTE
• VoWiFi
• VoNR
• 5G Core
• NSA
• SA

Repository Structure

telecom-call-flows/
│
├── LTE/
├── EPC/
├── IMS/
├── VoLTE/
├── VoNR/
├── 5G-Core/
├── Troubleshooting/
├── References/
├── Images/
└── README.md

⭐ Featured Procedure

LTE Attach Procedure

The LTE Attach Procedure is the first completed guide in this repository.

It includes:

• End-to-end LTE Attach signaling flow
• Message-by-message explanation
• Common troubleshooting scenarios
• References to relevant 3GPP specifications
• 📂 Location: LTE Attach Procedure

Learning Roadmap

LTE

Procedure	Status
Attach	✅ Completed
Tracking Area Update	🚧 Planned
Service Request	🚧 Planned
X2 Handover	🚧 Planned
S1 Handover	🚧 Planned
Paging	🚧 Planned
Detach	🚧 Planned

EPC

Procedure	Status
Default Bearer Creation	🚧 Planned
Dedicated Bearer Creation	🚧 Planned
Bearer Modification	🚧 Planned
Session Release	🚧 Planned
Idle Mode Mobility	🚧 Planned

IMS

Procedure	Status
IMS Registration	🚧 Planned
SIP Signaling	🚧 Planned
Session Establishment	🚧 Planned
Session Release	🚧 Planned

VoLTE

Procedure	Status
MO Call	🚧 Planned
MT Call	🚧 Planned
SRVCC	🚧 Planned
Emergency Call	🚧 Planned

VoNR

Procedure	Status
Registration	🚧 Planned
MO Call	🚧 Planned
MT Call	🚧 Planned
EPS Fallback	🚧 Planned

5G Core

Procedure	Status
Registration	🚧 Planned
PDU Session Establishment	🚧 Planned
Service Request	🚧 Planned
N2 Handover	🚧 Planned
Deregistration	🚧 Planned
Network Slice Selection	🚧 Planned

Progress

Technology	Progress
LTE	🟢 1 / 7 Procedures
EPC	⚪ Planned
IMS	⚪ Planned
VoLTE	⚪ Planned
VoNR	⚪ Planned
5G Core	⚪ Planned

Contributing

Suggestions, corrections, and constructive feedback are welcome.

If you identify an issue or have ideas for improvement, feel free to open an Issue or submit a Pull Request.

References

Content is developed using publicly available technical resources, including:

• 3GPP Technical Specifications
• RFC Documents
• GSMA Documentation
• Public technical papers

Author

Muhammad Usman

PS Core Engineer | Cloud Core Optimization Consultant

Specializing in LTE, EPC, IMS, VoLTE, VoNR, and 5G Core technologies.

Interested in Mobile Core Networks, Cloud Native Telecom, and Telecom Automation & Optimization

License

This project is licensed under the MIT License.

If you find this repository useful, consider giving it a ⭐ to support future telecom documentation.