SMPP Simulator (Go)

A simple SMPP (Short Message Peer-to-Peer) simulator written in Go, supporting SMS and USSD flows for both MO (Mobile Originated) and MT (Mobile Terminated) messages.
Includes:

• SMPP Server (handles SMPP clients, user simulators, USSD session management)
• SMPP Client (binds, sends/receives SMS and USSD, interactive menu)
• User Simulator (simulates a mobile user sending SMS/USSD to the server)

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Features

• SMPP v3.4 protocol support (basic subset)
• SMS and USSD MO/MT flows
• USSD session management (per user)
• Delivery receipts for SMS (optional)
• Simple user simulator (send SMS/USSD as a mobile user)
• Interactive SMPP client (send SMS/USSD, request delivery receipts)
• TLV support for USSD (ncs_id)
• Debug logging and raw PDU dumps

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Directory Structure

smpp-sim/
├── server/   # SMPP server code
│   ├── server.go
│   └── server_config.json
├── client/   # SMPP client code
│   ├── client.go
│   └── client_config.json
├── user/     # User simulator code
│   ├── user.go
│   └── user_config.json

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Quick Start

1. Build all components

cd smpp-sim/server && go build -o smpp-server
cd ../client && go build -o smpp-client
cd ../user && go build -o user-sim

2. Configure

Edit the server_config.json, client_config.json, and user_config.json files as needed.
Example server_config.json:

{
  "Port": 3001,
  "UserPort": 2776,
  "SystemID": "1",
  "Password": "password"
}

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3. Run the server

cd smpp-sim/server
./smpp-server

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4. Run the SMPP client

cd ../client
./smpp-client

• Use the interactive menu to send SMS or USSD, request delivery receipts, etc.

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5. Run the user simulator

cd ../user
./user-sim

• Enter messages in the format:
  FROM_NUMBER|TO_NUMBER|TYPE|MESSAGE_TEXT
  Example SMS: +12345|98765|SMS|Hello from user!
  Example USSD: +12345|98765|USSD|*123#
  Type exit to quit.

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USSD Session Management

• The server tracks USSD sessions per user (MSISDN/source address).
• USSD dialogs are routed based on session state.
• Sessions are cleaned up after 10 minutes of inactivity.

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Delivery Receipts

• If requested, the server simulates delivery receipts for SMS.
• Receipts are sent as deliver_sm with ESM class 0x04.

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Debugging

• All components print debug logs to the console.
• The server prints raw SMPP PDUs for troubleshooting.
• Wireshark can be used to inspect SMPP traffic on the configured ports.

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Notes

• This is a learning/demo tool, not a production SMSC.
• Only a subset of SMPP v3.4 is implemented.
• For advanced routing, multipart SMS, UCS2, etc., extend the code as needed.

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License

MIT or your preferred open source license.

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Authors

• Sripiranavan Yogarajah