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by anonymous


I had a bad experience in the past with Modbus, and before I commit to buy something I would like to know,

If anyone managed to get any of these products to work as a Serial RS485 to TCP Modbus **AND** also having multiple masters on the TCP side.

Thank you in advance


by anonymous
I have the same problem with RUT955 (FW RUT9_R_00.07.02.7): when more than one Modbus TCP Master is connected (at any poll rate), the RUT955 starts randomly (or so it seems) disconnecting the clients.

Do you have any news about this issue?

by anonymous

Since you have RUT955 MODBUS gateway listening on a single port, it is able to establish a single connection to a single master at once. It means that you can only query data from a single master, but, with different timing, you can establish connection from multiple masters in multiple locations.

Best regards,
by anonymous
See bellow I wrote you a comment about this issue.
by anonymous
Hello ZygimantasBliu,
what you are saying is not correct, because any TCP server can accept multiple connections on a single port, this is a native feature of TCP sockets: think of web servers, who only listen on port 80 (o 443) but they can serve webpages to hundreds of concurrent users.

Any commercial Modbus TCP gateway supports multiple concurrent connections from TCP masters, of course with some limits due to the compute resources available, but typically at least 8 or 16 connections are supported.

The gateway should simply send out the first request to the serial port and then wait for the device response (or timeout) before sending the next request from a different master, and so on in a round-robin fashion.

It should never break the TCP connection, unless the maximum number of concurrent connection is exhausted.


3 Answers

0 votes
by anonymous

These are the teltonika devices you might be interested to check:


RUT955 and RUT956


TRB145, TRB245, TRB255

For further details, visit the teltonika website and the wiki page:

I will also drop some links related to Modbus and RS485 functionalities. (RUT955 taken as device example)

I hope this helps to solve your query.

by anonymous

Dear Sir , 

About the Modbus gateway that’s okay , regarding the fact that it can have many masters in the TCP/IP version of Modbus that was never answered. 

Furthermore I had some bad experiences with Modbus being killed after several requests are these issues still going on ? 

Thank you in advance 

by anonymous

I'm sorry about your previous experience with the Modbus feature not working as expected. Our Research and Development department has worked on many improvements and fixes related to Modbus on many firmware releases. So you could check this information on the firmware download wiki page in the changelog section and see all the improvements and fixes related to Modbus since the firmware you were using on that occasion. Also, the RnD department recently announced that they are currently working on restructuring the Modbus functions in our devices; thus, we expect more changes and improvements on the Modbus features to come soon.

Below is the link to check the mentioned changelog (RUT955 taken as device sample):

Regarding the teltonika devices working as Modbus gateway and having multiple Modbus TCP masters, the devices in deed can reply with the data requested from different masters. However, I tested this feature with multiple master devices (four devices), and they worked fine until I set a poll rate period of 1 second; then,I started to get some inconsistency with the router processing simultaneous polls from different masters devices. I addressed my findings to our internal staff, and they will research more deeply on this subject. I will inform you about their comments as soon as I get an answer.

I hope this information helps with your current inquiry.

by anonymous

Dear Sir ,


Okay that is good to know,


I had a similar issue with Modbus when I was monitoring some alarm states with flag to push SMS out .. that was a pain to deal with and after dialling it in , I had another problem that after a while the connection was timing out .. (After a certain amount of requests)

and that was why I switched to another SMS gateway from the PLC manufacturer ( had some limits that I didn't like ) but I am willing to give teltonika another shot until I just send it to the bin again if I am not 100% satisfied with it :D )

Thank you in advance 

0 votes
by anonymous
Dear @AlessandroSalaGemmo

No I didn't find a solution for this problem and to be honest I didn't check it. So if the issue still persists you are pretty much screwed.

I never got an answer back from Teltronica for this issue even after having a remote session on my pc with Wire shark open and monitoring the pull requests.

As far as I know there is no known workaround.

The only workaround I found was reboot the service. But that is not easy to do since there is no CLI documentation with all the hidden services....

Ernestos tried to fix the situation but as I see the issue still is currently still active almost 2 something years onwards.

So hope is slim to be honest.

I hope you find some work around for you, please do post it please. If not ask teltronica support.
0 votes
by anonymous

I saw that since the last messages in this post, there has been an update regarding the Modbus functionality. I've found that they haven't yet solved the problem though. Is there any thought on when (or if) a fix can be expected, i.e., when multiple simultaneous TCP/IP connections to the gateway will be supported?

Kind regards,
by anonymous
Dear sir,

If this issue didn't got resolved by now you are pretty much screwed.

I had to switch to a siemends appliance.