To understand call flows, you must know the language of the EPC:
| Interface | Connection | Protocol | Purpose | | :--- | :--- | :--- | :--- | | S1-MME | eNodeB ↔ MME | S1-AP (Control) | Radio connection & mobility | | S1-U | eNodeB ↔ SGW | GTP-U (User) | User data tunneling | | S11 | MME ↔ SGW | GTP-C | Create/delete sessions | | S5/S8 | SGW ↔ PGW | GTP-C / GTP-U | Inter/intra-operator mobility | | S6a | MME ↔ HSS | Diameter | Authentication & subscription fetch | To understand call flows, you must know the
Illustration of a city skyline with towers, phones, and data streams labeled as "Netflix packet," "WhatsApp message," "Instagram video." Illustration of a city skyline with towers, phones,
You wake up, disable airplane mode → Your phone says "Hey tower, I'm back" → MME asks HSS "Is this user legit?" → PGW assigns an IP address → You see "LTE" in status bar. You wake up, disable airplane mode → Your
Entertainment angle: Like logging into a streaming service – authentication, session start, content ready.
Before a call flow begins, the network identifies the user and the device.
How streaming, gaming, and social media actually work under the hood – for tech enthusiasts, students, and entertainment lovers.