Serial LTE Modem AT#XSENDTO limited to 256 bytes of payload in one datagram

RE: Serial LTE Modem AT#XSENDTO limited to 256 bytes of payload in one datagram

Håkon Alseth — Mon, 28 Mar 2022 07:40:40 GMT

Hi Michal,

I'm glad to hear that the issue was resolved!

Hope you have a wonderful day!

Kind regards,

Håkon

RE: Serial LTE Modem AT#XSENDTO limited to 256 bytes of payload in one datagram

Michal Mühlpachr — Fri, 25 Mar 2022 23:47:45 GMT

Hi,

thank you, I am able to send up to 1402 UDP payload with v1.9.1 now.

It was some SLM AT dialogue timing issue probably.

Regards,
Michal

RE: Serial LTE Modem AT#XSENDTO limited to 256 bytes of payload in one datagram

Håkon Alseth — Wed, 09 Mar 2022 12:25:40 GMT

Hi,

Here's my test setup:

* ncs v1.9.0

* SLM with one modification: CONFIG_NRF_MODEM_LIB_TRACE_ENABLED=y

AT commands that I send:

at%xmodemtrace=1,2
at+cfun=1
AT#XSOCKET=1,2,0

AT#XSENDTO="example.com",1234
"Test UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDP"
++++++

Here it sends > 512 byte datagram, as shown in this pcap:

devzone.nordicsemi.com/.../trace_2D00_2022_2D00_03_2D00_09T12_2D00_21_2D00_49.077Z.pcapng

Kind regards,

Håkon

RE: Serial LTE Modem AT#XSENDTO limited to 256 bytes of payload in one datagram

Håkon Alseth — Wed, 09 Mar 2022 12:17:10 GMT

Hi,

Could you please provide how to reproduce this scenario?

[quote user="michalm"]In ncs v1.7 AT#XSENDTO with binary data (without <data> parameter, with data mode) SLM splits data to 256 bytes chunks of payload send in UDP datagram.
In ncs v1.9.1 AT#XSENDTO with binary data (without <data> parameter, with data mode) SLM splits data to 512 bytes chunks of payload send in UDP datagram.[/quote]

SLM in ncs v1.9.0, one change:

CONFIG_NRF_MODEM_LIB_TRACE_ENABLED=y

Here's my test scenario:

at%xmodemtrace=1,2
at+cfun=1
AT#XSOCKET=1,2,0

Here's the send command:

AT#XSENDTO="example.com",1234,"Test UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDPTest UDP"

Which returns:

#XSENDTO: 568

And here's the pcap that shows the frame sent as > 512 bytes:

devzone.nordicsemi.com/.../trace_2D00_2022_2D00_03_2D00_09T12_2D00_13_2D00_05.383Z.pcapng

Kind regards,

Håkon

RE: Serial LTE Modem AT#XSENDTO limited to 256 bytes of payload in one datagram

Michal Mühlpachr — Wed, 09 Mar 2022 11:37:04 GMT

We would like to utilize MTU as much as possible. We are sure, that datagrams with 1400 bytes travels fine through LTE/EPS with other modems.

RE: Serial LTE Modem AT#XSENDTO limited to 256 bytes of payload in one datagram

Michal Mühlpachr — Wed, 09 Mar 2022 11:29:01 GMT

In ncs v1.7 AT#XSENDTO with binary data (without <data> parameter, with data mode) SLM splits data to 256 bytes chunks of payload send in UDP datagram.
In ncs v1.9.1 AT#XSENDTO with binary data (without <data> parameter, with data mode) SLM splits data to 512 bytes chunks of payload send in UDP datagram.

RE: Serial LTE Modem AT#XSENDTO limited to 256 bytes of payload in one datagram

Håkon Alseth — Tue, 08 Mar 2022 13:25:43 GMT

Hi,

Could you share which version of ncs that you are using, and a bit more detailed information about the issue that you're seeing?

Splitting packets on the uart interface shall not be the same as splitting it on a socket interface.

The maximum size of a single udp datagram is defined in the xsendto:

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/1.9.0/nrf/applications/serial_lte_modem/doc/SOCKET_AT_commands.html#udp-send-data-xsendto

Kind regards,

Håkon