KTCP_DATA limit on HL7800?


There seems to be a limit when I try to send data over TCP to an HL7800 modem. After sending a certain amount of bytes, the +KTCP_DATA urc always returns +KTCP_DATA: 1,1629 and the EOF pattern is printed prematurely, so there is a limit. The number 1629 is not always consistent either, as I sometimes get less than that. Trough Wireshark I can see that the right amount of bytes is being sent.

data_mode is not supported so the 1500 byte limit should not be there.

Any ideas?


do you find problem in +KTCPSTART?

The problem occurs when sending data to the device while the TCP connection is already established.

It’s established with AT+KTCPCNX

you can still use +KTCPSTART

So there is a bug somewhere? Is that bug known?

I can’t just change the command into production.

if no problem is found in +KTCPSTART, may need to investigate if this is server problem

The server transmits correctly, as I noted wireshark shows the correct amount of bytes sent.

Does using KTCPSTART make any difference? Why would that be?

Does KTCPSTART return the same replies as TCPCNX does?


actually what is the problem then if it send correct amount of data?
do you mean you don’t want the EOF?

Server sends correct amount but modem reads less bytes

then if you don’t see problem in +KTCPSTART, that means it is network issue, right?

I haven’t tried KTCPSTART yet. What is the difference with KTCPCNX?

it is different command to +KTCPCNX
you can see AT command user guide

Here also says how to capture wireshark log in HL7800 to verify if this is network problem:

Ok, so could it be that multiple KTCPDATA messages appear and the payload is split into different packets?

you need to capture the wireshark on module side to understand this

Ok, will get back on this. Thanks

you might need to also try with +KTCPSTART to get more clue

I just realized that what’s happening is the payload is split into packets and I have to continue sending KTCPRCV command to get the whole payload. That’s tricky to manage. Is that something the modem itself is doing, just for reference?

probably yes, might also depends on how fast the host reads the data