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====== Coverage of metrics by OSI levels ======

<mermaid>
graph LR
    L1["L1 Physical<br/>NIC counters via system"]
    L2["L2 Data Link<br/>MAC, VLAN"]
    L3["L3 Network<br/>IP, IPSec ESP, GTP-U"]
    L4["L4 Transport<br/>TCP/UDP/SCTP"]
    L5["L5 Session<br/>GTPv2-C, IKEv2"]
    L6["L6 Presentation<br/>IKEv2/IPSec encryption, EAP-AKA'"]
    L7["L7 Application<br/>Diameter, service bearer ops"]
    Operations["Operations<br/>KPI, SLA, Capacity"]
    CX["CX Level<br/>Subscriber Experience"]

    L1 --> L2 --> L3 --> L4 --> L5 --> L6 --> L7 --> Operations --> CX

    style L1 fill:#e74c3c,color:#fff
    style L2 fill:#e67e22,color:#fff
    style L3 fill:#f39c12,color:#fff
    style L4 fill:#2ecc71,color:#fff
    style L5 fill:#1abc9c,color:#fff
    style L6 fill:#3498db,color:#fff
    style L7 fill:#9b59b6,color:#fff
    style Operations fill:#34495e,color:#fff
    style CX fill:#2c3e50,color:#fff
</mermaid>

===== Detailing metrics by level =====
OSI model:

^ Level                           ^ Metrics  ^ Examples                                                                                                                                                 ^
| **L1/L2 Physical / Data Link**  | -        | Covered by a separate node_exporter or equivalent at the OS level (not included in the ePDG metrics list)                                                |
| **L3 Network / IPSec tunnels**  | 3        | ''epdg_gtpu_packets_total'', ''epdg_gtpu_bytes_total'', ''epdg_gtpu_errors_total'' — GTP-U data plane                                                    |
| **L4 Transport**                | 1        | ''epdg_network_connection_status'' — TCP connections to nodes (PGW/AAA/HSS)                                                                              |
| **L5 Session**                  | 3        | ''epdg_session_ike_sa_total'', ''epdg_session_child_sa_total'', ''epdg_session_gtp_sessions_total''                                                      |
| **L6 Presentation/Security**    | 3        | ''epdg_ikev2_messages_total'', ''epdg_ikev2_request_duration_seconds'', ''epdg_ikev2_errors_total'' — IKEv2/IPSec encryption and EAP-AKA authentication  |
| **L7 Application**              | 9        | ''epdg_diameter_*'' (SWm/SWx/S6b, 5 metrics), ''epdg_gtp_*'' (GTPv2-C, 4 metrics)                                                                        |

Operator level:
^ Level ^ Metrics ^ Examples ^
| **Operations** | 11 | ''epdg_service_availability'', ''epdg_service_uptime_seconds'', ''epdg_app_*'' (3), ''epdg_system_*'' (4), ''epdg_config_*'' (2) |
| **Customer Experience** | 3 | ''epdg_service_attach_duration_seconds'' p95, ''epdg_service_attach_total'' (success rate), ''epdg_ikev2_request_duration_seconds'' p99 |

===== Level 9: Quality of VoWiFi service perception =====

^ QoE indicator ^ Source metrics ^ Interpretation ^
| **VoWiFi connection time** | ''epdg_service_attach_duration_seconds'' p95 | > 3 seconds — subscriber notices delay when switching to WiFi |
| **Continuity of service** | ''epdg_session_ike_sa_total'' delta | Mass discharge > 50 IKE SA = accessibility issue |
| **Authentication success** | ''ePDG_High_Attach_Failure_Rate'' alert rate | > 5% = HSS/AAA node problem |
| **Delayed appointment bearer** | ''epdg_gtp_request_duration_seconds{msg=create-session}'' p99 | > 500 ms — delayed availability of voice channel |
| **GTP-U tunnel** | ''epdg_gtpu_errors_total'' rate / ''epdg_gtpu_packets_total'' | > 0.1% = degradation of voice quality |
| **IKEv2-reliability** | ''epdg_ikev2_errors_total'' by type | NO_PROPOSAL_CHOSEN / AUTHENTICATION_FAILED — problems with certs / UE |