TCP Node - message splitting question

General
1

I am sending 40,002 byte TCP packet from a microcontroller and reading it into Node-RED from the TCP node.

I'm reading the contents of the buffer using the debug node.

  1. The TCP packet seems to end up as two messages in Node-RED. Here you can see the sizes:
    image
    image643×519 38.7 KB

Is there any rhyme or reason as to why they are split or in what proportion?

  1. Is there a good way to detect disconnections? If I reset the microcontroller, it seems to show in the node status that one connection exists. Then when I restart the MCU it sometimes sees two connections, and sometimes seems to disconnect the first one. Any ideas why that may be?
2

From Google -

Ethernet traffic moves in units called frames. The maximum size of frames is called the Maximum Transmission Unit (MTU). When a network device gets a frame that is larger than its MTU, the data is either fragmented into smaller frames, or dropped. ... An Ethernet packet larger than 1500 bytes is called a jumbo frame .

3

Thanks, but how does this explain the message segmentation shown above?

4

Fair point, does it always split at the same sizes ?

5

It does seem to split into the same buffer sizes, when the same number of bytes are sent.

However if I send different numbers of bytes in the first place, the message splitting can be different.

6

I guess you can join the two payload together, but as to why it splits as it does I'm not sure.
Maybe there is a setting in NR that needs tweaking ?
You will need to wait for the smart people to help out :wink:

7

How do you have the tcp in node configured ? Which version of Node-RED ? Which OS are you running on ?

8

Hi, it's:

OS: Ubuntu 20.04.2 LTS
NodeRED version: 2.0.4

Here is how I have configured the TCP node:

image
image885×588 21.8 KB

9

Have you tried output single buffer ?

10

@hazymat Did you get anywhere with this ?

11

I tried setting output to single buffer, but it doesn't return anything. (Client connects okay, but no packets are shown on debug output)...