Fix Mermaid syntax in ARCHITECTURE.md

ARCHITECTURE.md

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+# Private 5G Network Architecture
+
+This repository contains a step-by-step guide to setting up a Private 5G/LTE Network using Open Source software and generic hardware.
+
+## System Overview
+
+The system implements a full 5G network stack, consisting of the following key components:
+
+1.  **User Equipment (UE)**: A Commercial Off-The-Shelf (COTS) smartphone or modem with a programmable SIM card.
+2.  **Radio Hardware**: USRP B210 (Software Defined Radio) acting as the RF frontend.
+3.  **Radio Access Network (RAN)**: `srsRAN` (specifically `srsenb` or `srsgnb`) handling the base station logic.
+4.  **Core Network (CN)**: `Open5GS` providing 5G Core functions (AMF, SMF, UPF, AUSF, UDM, etc.).
+5.  **External Network**: The host machine's internet connection, accessed via NAT/IP Forwarding through the `ogstun` interface.
+
+## Architecture Diagram
+
+The following diagram illustrates the data flow and logical connections between components.
+
+```mermaid
+graph TD
+    subgraph "User Domain"
+        UE["COTS UE<br/>(Smartphone)"]
+        SIM["Programmable SIM<br/>(sysmoISIM)"]
+        UE --- SIM
+    end
+
+    subgraph "Radio Access Network (RAN)"
+        USRP["USRP B210<br/>(SDR Hardware)"]
+        srsRAN["srsRAN gNodeB<br/>(Software)"]
+
+        UE -.->|"Radio Interface<br/>(Air)"| USRP
+        USRP ---|"USB 3.0"| srsRAN
+    end
+
+    subgraph "Core Network (Open5GS)"
+        AMF["AMF<br/>(Access & Mobility)"]
+        UPF["UPF<br/>(User Plane Function)"]
+        SMF["SMF<br/>(Session Management)"]
+        MongoDB[("MongoDB")]
+
+        srsRAN --"NGAP/SCTP"--> AMF
+        srsRAN --"GTP-U/UDP"--> UPF
+        AMF <--> SMF
+        SMF <--> UPF
+        AMF <--> MongoDB
+    end
+
+    subgraph "Data Network"
+        TUN["ogstun<br/>(Tun Interface)"]
+        NAT["NAT / IP Forwarding"]
+        Internet["Internet<br/>(External Network)"]
+
+        UPF <--> TUN
+        TUN <--> NAT
+        NAT <--> Internet
+    end
+
+    %% Styles
+    classDef hardware fill:#f9f,stroke:#333,stroke-width:2px;
+    classDef software fill:#bbf,stroke:#333,stroke-width:2px;
+    classDef network fill:#dfd,stroke:#333,stroke-width:2px;
+
+    class UE,USRP,SIM hardware;
+    class srsRAN,AMF,UPF,SMF,MongoDB software;
+    class TUN,NAT,Internet network;
+```
+
+## Key Configuration Parameters
+
+Based on the documentation steps:
+
+*   **MCC (Mobile Country Code)**: `001` (Test Network)
+*   **MNC (Mobile Network Code)**: `01` (Test Network)
+*   **TAC (Tracking Area Code)**: `7`
+*   **Network Interface**: `ogstun` (Created by Open5GS for handling user traffic)
+*   **Drivers**: UHD (Universal Hardware Driver) for USRP communication.
+
+## Data Flow
+
+1.  **Registration**: The UE communicates via the USRP to srsRAN, which forwards the request to the AMF in Open5GS for authentication (using SIM credentials stored in MongoDB).
+2.  **Session Establishment**: Once authenticated, the SMF establishes a PDU session and configures the UPF.
+3.  **Traffic Flow**: User data sent from the UE goes through the USRP -> srsRAN -> UPF -> `ogstun` -> NAT -> Internet.