Pre-established connection questions

By labasvakaras, 19 January, 2026
Forums
Gurux.DLMS

Hello, i wanted to get more information about pre-established connection, because i want to use DLMS with smart water meter on NB IoT.

1. As i understand with pre-established connection AARQ/AARE/SNRM messages are not being delivered, but you have to configure client/server before connection, yes?
2. With pre-established only two packets are being sent - one with data and acknowledge from client?
3. Client settings must be the same as server - i mean conformance, ciphering info etc... What happens if it does not match and how client/server knows that it is corrcet?
4. Auto connect object - this is object used in server right? And you connect directly to client or is it that you open socket for listening?

Kurumi

3 weeks 6 days ago

Hi,

1. Client can't ask server settings when pre-established connection is used and client must know what settings to use. The correct settings are usually defined in the meter documentation.

2. If all data is fit to one packet there are only two messages. If you are reading e.g. profile generic, it might be that there are multiple frames send between the client and meter.

3. If block cipher or authentication key is not correct, the meter returns usually ciphering error.

4. Auto connect object defines the IP address where the meter try to establish the connection. You can read more from here:

https://gurux.fi/Gurux.DLMS.Objects.GXDLMSAutoConnect

BR,
Mikko

labasvakaras

3 weeks 6 days ago

does your example DLMS servers and clients support pre-established connection? i want to test it

Kurumi

3 weeks 6 days ago

Hi, Yes, you can try it. Get GuruxDLMSServerExample. This example is using malloc, but the idea is the same. Select Gurux as meter manufacurer in GXDLMSDirector. Set authentication to HighGMAC and client address to 2.

 

 

Select Secured connections and set 

system title:Gurux123

Block cipher key:000102030405060708090A0B0C0D0E0F

Authentication key: D0D1D2D3D4D5D6D7D8D9DADBDCDDDEDF

Pre-established connections don't support the association view, and you need to add COSEM objects manually. Select "Edit" and "Add Object...". Select Clock as object type and press OK.

Establish the connection to the meter, and you can read the clock object. Add other objects that you want to read in the same way.

BR,

Mikko