Keep-alive message is not working

Hello Mikko,

I hope the holidays went well. I was implementing a client application and I don't want my client to timeout because of the meter's timeout time setted. So what I am trying is sending a keepalive message to the meter before it times out and closes the connection.

But when I do that without making any modifications to gurux.dlms package, only by calling the keepAlive method in the GXDLMSClient class, it throws an exception and just closes the connection and I can not send a message after that.

Here is the bytes sent for keep alive as a request and received response.
-> 7E A0 08 02 21 09 B1 E6 3E 7E
<- 7E A0 08 09 02 21 B1 5F FF 7E
and the connection times out after that and throws an exception.

So I looked into the GXDLMSClient class, keepAlive() method and it is not calling the getKeepAlive() method of the GXDLMSSettings class, rather it is calling the getRecieverReady() method.

public final byte[] keepAlive() {
// There is no need for keep alive in IEC 62056-47.
if (this.getInterfaceType() == InterfaceType.WRAPPER) {
return new byte[0];
}
return GXDLMS.getHdlcFrame(settings, settings.getReceiverReady(), null);
}

I don't know if you have done that on purpose or if it was an error so I changed the implementation of the method to the below code and recompiled and packaged it again and used it.

public final byte[] keepAlive() {
// There is no need for keep alive in IEC 62056-47.
if (this.getInterfaceType() == InterfaceType.WRAPPER) {
return new byte[0];
}
return GXDLMS.getHdlcFrame(settings, settings.getKeepAlive(), null);
}

Changed only settings.getReceiverReady() to settings.getKeepAlive(). Now the connection doesn't timeout but I am facing a header CRC problem in the requests I send to the meter after the keepalive is performed.

Below is the byte that is sent as a keepalive request and the received reply from the meter.

-> 7E A0 08 02 21 09 B1 E6 3E 7E
<- 7E A0 08 09 02 21 D1 59 9C 7E

After the above request and response, the client changes the header CRC of the request messages generated and send to the meter and causing a checksum problem.

Here are the bytes that I generated to read the same object before and after keep-alive is sent to the meter.

before keepalive request, I was able to read from the meter with this request
-> 7E A0 1A 02 21 09 BA FD 22 E6 E6 00 C0 01 C1 00 01 00 00 60 02 0C FF 02 00 71 2A 7E

after keepalive request, the header CRC of the read request is changed and I can not read from the meter, it causes a checksum error
-> 7E A0 1A 02 21 09 DC CD 24 E6 E6 00 C0 01 C1 00 01 00 00 60 02 0C FF 02 00 71 2A 7E

I did not change any inputs or parameters in between requests.

I can not figure out why it is changing the header CRC and I am not sure if I should keep using the keepalive method of the GXDLMSClient class with settings.getReceiverReady() or settings.getKeepAlive() method.

If you please help me figure out what is happening here I would appreciate it.
Thank you in advance.

Sincerely,
Adonay Eshetu