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I need to design an embedded sotfware that will drive a LTE cellular device (like u-Blox TOBY L2 Series) and its TCP/IP stack to transmit some data toward a distant server.

I'm waiting for the device to be delivered at work. For now, I use a GPRS device (u-Blox LEON series). Basically I perfom the following commands :

  • Configure PSD profile with AT+UPSD
  • Activate PSD profile with AT+UPSDA=0,3
  • Open socket with AT+USOCR=6
  • Connect to server IP with AT+USOCO=0,"xx.xxx.xx.xxx","pp" where xx is the IP address and pp is the port number
  • Write data with AT+USOWR

This is a very basic flowchart, I don't need very specific settings, just the default one. I do not configure a PDP context with AT+CGDCONT or anything else. Maybe the configuration of the PSD with AT+UPSD is enough with both GPRS and LTE network.

The problem is the following : Apparently there are some differences between GPRS/UMTS devices and LTE devices when it comes to set up the network configuration (PDP context for GPRS/UMTS devices and EPS for LTE). I have read quite everything about these data session setups but I don't manage to fully understand the differences.

So when I will switch from GPRS device (LEON) to LTE device (TOBY), what differences will occur in terms of setups and/or AT commands?

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First of all, you may be advised, that as far as I am aware, the TCP socket support for TOBY-L2 is under development for most modules, except for the L201 version (see current datasheet and AT command reference at ublox.com), and for other versions using the most recent firmware update. I'm not linking to anything directly here, as ublox seems to be restructuring its website right now.

Other than that, the AT commands reference is quite the resource here, it details the differences in each command between TOBY, LEON, SARA and LISA as well as their versions. If you didn't read it, here is a (not necessarily complete or actually checked) list for migration, taken from exactly that document:

  • +UPSD: Parameter values depend quite a bit on the modem type. param_tag and param_val have many special meanings and restrictions for LEON. If you use any of those, be advised to take special measures. TOBY-L2 also has a restriction, however, that should be easily avoided
  • +UPSDA: no differences, but a side effect: If you activate a profile with the same number on TOBY-L2 twice, but with different settings, that may fail. Have a look at the manual if you do that.
  • +USOCR: You can only create 7 sockets (0-6) on TOBY-L2 as compared to up to 16 sockets on LEON.
  • +USOCO: No apparent differences
  • +USOWR: There is some weirdness with LEON in the details in case you're also receiving data, which you obviously don't, so you're fine here.

However, pay attention that you do not mix +CG* and +UPS* commands in your application, in case you're upgrading. That may lead to problems.

Other than that I can not discern any other differences in the documentation. Still, it may just not be documented at a stage this early.

There are two other references I can point you to.

  • As soon as you have an actual TOBY module with you, try the m-center. It allows you to set up PSD profiles and trace the AT commands at the same time.
  • Contact your distributor. u-blox has quite detailed agreements with them, in general, which makes them responsible for supporting you in questions like that.
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