EPC — Evolved Packet Core¶

flowchart LR
    subgraph RAN ["Radio Access Network"]
        UE[📱 UE]
        eNB[📡 eNB]
    end

    subgraph EPC ["Evolved Packet Core"]
        MME[MME<br/>Mobility Mgmt]
        HSS[(HSS<br/>Subscriber DB)]
        SGW[SGW<br/>Serving GW]
        PGW[PGW<br/>PDN GW]
    end

    Internet((🌐 Internet))

    UE <-->|LTE Air| eNB
    eNB <-->|S1-MME| MME
    eNB <-->|S1-U| SGW
    MME <-->|S6a| HSS
    MME <-->|S11| SGW
    SGW <-->|S5/S8| PGW
    PGW <-->|SGi| Internet

sequenceDiagram
    participant UE as 📱 UE
    participant eNB as 📡 eNB
    participant MME as MME
    participant HSS as HSS
    participant SGW as SGW
    participant PGW as PGW

    UE->>eNB: 1. RRC Connection Request
    eNB->>MME: 2. Initial UE Message (S1AP)
    MME->>HSS: 3. Authentication Request (S6a)
    HSS-->>MME: 4. Auth Vectors
    MME->>UE: 5. Auth Challenge
    UE-->>MME: 6. Auth Response
    MME->>SGW: 7. Create Session Request
    SGW->>PGW: 8. Create Session Request
    PGW-->>SGW: 9. Create Session Response (IP allocated)
    SGW-->>MME: 10. Create Session Response
    MME->>eNB: 11. Initial Context Setup
    Note over UE,PGW: Bearer established - Data can flow