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G120 + Sim900 + TLS


#1

I have a G120 and I am using an arduino shield from seeedstudio which contains a Sim900 chip I am using to communicate with a hand built server.

The SeeedStudio Shield
http://www.seeedstudio.com/depot/gprs-shield-v20-p-1379.html?cPath=132_134

I am using a slightly modified version of the TCP Cellular Radio Manager from codeplex

To connect to the TCP socket server the command is
AT+CIPSTART=“TCP”,“http://myserver”,“443”

The issue is that even though I am connecting to my server on 443, I can’t get it to start tls. I have looked through the manual for AT commands in starting TLS on a TCP connection, but it doesn’t seem to mention it anywhere. I know that there is an SSL / TLS Stack included in the G120 for networking, but I am unsure how to utilize this when the tcp connection is being established on the sim900 which is connected to the G120 through a serial connection.

I am not 100% sold on the Sim900. The overall picture is that I need to come up with a method of connecting my G120 to a server through a GPRS connection. Does anyone have any experience in this kind of connection?


#2

This is one of the reasons some of us having been nagging GHI to sort out PPP for 4.2 and we know it’s on their list but not a high priority at the moment.

With PPP on 4.1 you didn’t have to worry about any of this. You simply dialed the connection via PPP and then you could use sockets to talk to servers, email etc.

I have this working to multiple servers on a ChipworkX module and now that the G400 replaces this, I am having the same issues as yourself on how to integrate it. It’s not a simple case of using AT commands as they only give you a serial stream connection and this does not tie in directly to the underlying TCP stack within 4.2

I am looking at how to do this just now and have an idea to use sockets within 4.2 and have a serial to TCP connection that handles the through put of the data but I am still a few days away from testing this. I am still waiting for the modems from Seeed as they are stuck in damn customs here.

By the way, I have been using the SIM900 modules for about 3 years now and they work very well so don’t give up on them yet. I think your issue is more to do with the integration the serial stream and the underlying TCP and use of TLS.


#3

Thanks for the reply. I am a little new to this and was curious if you could provide any additional information on how to communicate through the sim900 using ppp. Does this replace the need for AT commands. I would love to catch up to speed and assist in any testing and driver support for this. Also, even though 4.2 doesn’t include ppp, doesn’t the GHIPremium library supports this in 4.2?


#4

There is no PPP support in 4.2 at present. If you need this, add your wish for it :slight_smile:

I was hoping to have my Seeed Cellular Modems here this week but with it being local holiday they are stuck in customs so I won’t be able to work on it next week whilst I am away so it will be the week after this.


#5

http://www.gprsbee.com/

I too looking forward to GPRS…was not aware we had to use PPP…yes…a vote from me


#6

@ Dave any guide on how to get the GPRS working with G120? or do i have to wait?


#7

Crossing my fingers Dave…


#8

That’s a neat board - thanks for sharing!


#9

FYI noticed this on Dangerous Prototypes today, a SIM900 board

http://dangerousprototypes.com/forum/viewtopic.php?f=19&t=5905#p54609