TCPServer on Electron

fbt · July 24, 2017, 10:24am

Hi!, is the TCPserver functionality currently impleented on Electron’s firmware? if not, which alternatives are available? thanks.

rickkas7 · July 24, 2017, 4:16pm

TCPServer cannot be used with the Particle SIM because the mobile carrier network does not allow inbound TCP connections. It probably won’t work with most 3rd-party SIM cards for the same reason.

It theoretically could work with a VPN-based SIM card, however in practice it does not appear to work, either.

You’ll need to use outbound connections (either TCP or UDP) to a server on the Internet, instead.

Here’s a lot of technical information on why various inbound techniques don’t work, at least with the Particle SIM card, because of security restrictions on the mobile carrier network:

github.com

rickkas7/particle_notes/blob/master/electron-low-level-networking.md

# Electron low-level IP networking tips

Your mobile data provider generally uses shared IP addresses for mobile devices, including both Electrons and phones. The devices sit behind NAT (Network Address Translation) with port forwarding, similar to how your home devices share a single IP address from your cable or DSL provider.

The short answer is: the network is more secure than you might guess, but this also makes peer-to-peer transmission nearly impossible. You pretty much have to transit data through a well-known server on the Internet.

I ran these tests using the Particle SIM on the AT&T network in the United States. 


## UDP outbound: Beware of the port

The most common situation is when you're using UDP to communicate with a server you control on the Internet. When you do this, make sure your server responds to the port the request came from, not the port the Electron is listening on!

Also, the return channel will only stay active for a period of time. For the Particle SIM, this could be as long as 23 minutes. For some other mobile providers, it could be as short as 30 seconds before the port forwarding is disabled.

Incidentally, this is what the [Particle keep-alive](https://docs.particle.io/reference/firmware/electron/#particle-keepalive-) is for; it's to keep the port forwarding for the cloud DTLS connection alive. Note that it only keeps the cloud DTLS ports alive; if you are doing your own private UDP port forwarding you need to keep your own port forwarding alive by sending packets to or from the port.


Here's a sample program for the Electron to send some data to a server on the Internet:

This file has been truncated. show original

fbt · July 25, 2017, 7:57am

Thanks a lot @rickkas7. in our particular case, we need to use the electron as a TCPserver in order to transfer a bunch of samples to a TCPclient implemented on a Node.js server (so the data flow is always from Electron to Node.js) … so as i understand from your answer, that is not possible with TCP …but it is still not possible with UDP? thanks again for your support.
best regards

rickkas7 · July 25, 2017, 10:29am

TCP is bi-directional, the client-server only determines which side starts the connection.

Typically the node.js side runs the TCP server. That makes sense because the server side must have a known and accessible IP address. The Electron’s IP address, in addition to not being known, is not accessible.

The TCPClient on the Electron makes a connection to the node.js server, and can either send data to node.js, or receive data from it. Both work.

This is an example of a node.js TCP server with a Photon sending data to it, but it works the same with the Electron (when the server has a publicly accessible IP address).

Brewskey · July 25, 2017, 7:28pm

Yeah @fbt, it sounds like you should just be using webhooks to communicate with your node server. Running a full-blown TCP server on an electron seems like overkill.

fbt · July 26, 2017, 8:54am

Hi @Brewskey … the problem is that the data i have to send is more than a webhook supports … i’ll try to implemente the TCP client on the Electron, as @rickkas7 proposed. thanks!!!

KyleG · July 26, 2017, 6:18pm

Let us know if this works for you!

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TCPServer on Electron

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