> For the complete documentation index, see [llms.txt](https://docs.monogoto.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.monogoto.io/ntn-satellite-networks/udp-communication-for-ntn-applications/murata-type-1sc-send-receive-udp-data.md).

# Murata Type 1SC: Send/Receive UDP Data

Start sending data to a UDP server, and from the server back to the device. For more information about getting started with the Murata Type 1SC, visit [this guide](/ntn-satellite-networks/ntn-certified-devices/ntn-certified-modules/murata-lbad0xx1sc-dm-satellite-ntn-network.md).

***

#### 1. Send data from your device

**Open a UDP Socket**

Replace <mark style="color:red;">`YOUR_SERVER_IP`</mark> and <mark style="color:red;">`PORT`</mark> with your server's ip address and port.

```
AT%SOCKETCMD="ALLOCATE",1,"UDP","OPEN","YOUR_SERVER_IP",PORT
```

Expected Response: `SOCKETCMD: 1`

**Set Socket Options and Activate the socket**

```
AT%SOCKETCMD="SETOPT",1,36000,1
AT%SOCKETCMD="ACTIVATE",1
```

Expected Response: <mark style="color:red;">`OK`</mark>

**Send UDP Payload**

Send the message <mark style="color:red;">`Hello World`</mark> encoded to hex using [RapidTables](https://www.rapidtables.com/convert/number/ascii-to-hex.html): <mark style="color:red;">`48656C6C6F20576F726C64`</mark>:

```
AT%SOCKETDATA="SEND",1,11,"48656C6C6F20576F726C64"
```

Expected Response: <mark style="color:red;">`%SOCKETDATA: 1,11`</mark>

{% hint style="info" %}
The payload: "Hello World" is 11 bytes in size. If you're sending a different payload, make sure to count the exact number of characters you send.
{% endhint %}

**Close the Socket**

```
AT%SOCKETCMD="DELETE",1
```

Expected Response: <mark style="color:red;">`OK`</mark>

On your server terminal, you should see:

```
Hello World
```

{% hint style="success" %}
Is the uplink working? Nice! Let's continue with bidirectional communication
{% endhint %}

***

#### 2. Enable Downlink (Server → Device)

The SIM by default doesn't have a public IP address, hence can only send a downlink **immediately after receiving an uplink**, before the socket clses. The server responds using the same IP address and port from which the data was received.

To test this, you'll need a UDP server that sends a response. You can use <mark style="color:red;">`socat`</mark> with a script that logs incoming data sent to port <mark style="color:red;">`9000`</mark> and sends "**ACK**" as a response:

```bash
socat UDP4-RECVFROM:9000,fork SYSTEM:'tee /dev/stderr > /dev/null; echo ack'
```

***

#### 3. Test Bidirectional Communication

On your device, send data and wait for a response.

**Start by opening the UDP port and send data to your UDP server:**

Change <mark style="color:red;">`YOUR_SERVER_IP`</mark> with your server's IP address.

```
AT%SOCKETCMD="ALLOCATE",1,"UDP","OPEN","YOUR_SERVER_IP",9000
AT%SOCKETCMD="SETOPT",1,36000,1
AT%SOCKETCMD="ACTIVATE",1
AT%SOCKETDATA="SEND",1,11,"48656C6C6F20576F726C64"
```

The response <mark style="color:red;">`%SOCKETEV: 1,1`</mark> (not <mark style="color:red;">`%SOCKETCMD: 1`</mark> ) indicates that a packet was received.

**Read incoming UDP data**

```
AT%SOCKETDATA="RECEIVE",1,1500
```

Example Response: <mark style="color:red;">`%SOCKETDATA: 1,1,1,"61636B0A","Sender_IP",PORT`</mark>

{% hint style="info" %}
The hex string <mark style="color:red;">`61636B0A`</mark> decodes to <mark style="color:red;">`ack`</mark>)
{% endhint %}

**Close the Listener Socket**

```
AT%SOCKETCMD="DELETE",1
```

Expected Response: <mark style="color:red;">`OK`</mark>&#x20;

{% hint style="success" %}
Do you see the data appearing in the server, as well as the received downlink "**ACK**"? Great work!
{% endhint %}

***

## 🛰️ Listen for incoming UDP packets

Follow the steps below to configure the EVK in "server mode" (listening on a specific port).&#x20;

Requirements for sending UDP data to the Murata kit:

* **Public IP Mapping (NAT) or VPN Configuration**\
  Ensure the EVK is reachable via a public IP address, either through NAT port forwarding or a VPN tunnel. This is essential for delivering UDP packets to the device.
* **Static IP Assignment**\
  Assign a static IP address to the device within your APN to ensure consistent and reliable routing.

**Allocate UDP Socket in Listen Mode** (e.g., port 9000)

```bash
AT%SOCKETCMD="ALLOCATE",1,"UDP","LISTEN",,,9000,,,1
```

Expected Response: <mark style="color:red;">`%SOCKETCMD: 1`</mark>

**Activate the Listener**

```bash
AT%SOCKETCMD="ACTIVATE",1
```

Expected Response: <mark style="color:red;">`OK`</mark>

**Verify Listener Info (Optional)**

```bash
AT%SOCKETCMD="INFO",1
```

Expected Response: <mark style="color:red;">`%SOCKETCMD: "ACTIVATED","UDP","EVK_IP",,,9000`</mark>

**Send a UDP Message**

{% hint style="info" %}
Now use the UDP Sender application on your PC to send a UDP message to the EVK’s IP address and listening port.
{% endhint %}

**Wait for UDP Event Notification**

The modem will notify when a packet is received:

```
%SOCKETEV: 1,1
```

**Read Incoming UDP Data**

```bash
AT%SOCKETDATA="RECEIVE",1,1500
```

**Example Response:**

```
%SOCKETDATA: 1,1,1,"48656C6C6F0D0A","<Sender_IP>",54532  
OK
```

*(The hex string `"48656C6C6F0D0A"` decodes to `Hello`)*

**Close the Listener Socket**

```bash
AT%SOCKETCMD="DELETE",1
```

**Expected Response:**

```
OK
```

***

### Troubleshooting

* **No data received on server**: Check your firewall allows UDP port 9000 (`ufw allow 9000/udp`)
* **Connection timeout on device**: Verify the server IP address is correct
* **No downlink received**: Make sure to call `AT#XRECV` before closing the socket
* **General connectivity issues**: Check device logs at [hub.monogoto.io](https://hub.monogoto.io) to verify device registration and connection status