MOD-USB3G over MOD-GSM

[markr]

We need internet connectivity over a cellular network for a A20. Mostly UMTS/3G, but sometimes we have to sit at GRPS. Olimex makes boards like MOD-GSM but also UMTS dongles like MOD-USB3G. I wonder, are there any advantages of the lower speed (max EDGE) and considerably more expansive boards over the dongle? Why doesn't everyone uses these dongles for GSM connection? Are they less reliable, more energy hungry. What do I miss?

Thanks, Mark

[N8body]

The Usb Variants mostly dont have Audio-Support,they can just connect to a 3g Network and route "internet". Also consider that the "USB" Variant is only a consumer USB UMTS Stick,which can break down very easily,especially when used in 24/7 Mode.

[MBR]

The another problem with USB UTMS sticks is modeswitching - after power up, they apear as USB-conected CD-ROM drive (with Windows apps, drivers and such) and they need some heavy magic (handled by modeswitch command, invoked by udev) to switch to "modem mode", where they apear as a bunch of USB-to-serial convertors. The modeswitching may take some time, because the device has to initialize itself, settle down and be scanned twice. Luckily, some devices, at least Huawei ones, can be reconfigured by special AT commands to disable CD-ROM and SD card reader, so they start in modem mode by default and does not need modeswitching, see https://wiki.archlinux.org/index.php/Huawei_E1550_3G_modem#AT_commands.

And yes, they are energy hungry - peak RF power is 2W, 20x more than WiFi. But if they don't have to work all the time, they can be used, as long as they don't overheat.

[dudo]

Does anyone know if this MOD-USB3G from olimex supports CDC ethernet or is USB-serial modem? Witch CDC ethernet one can configure 3G connection over eth interface (kernel driver is cdc_ether) without need for wvdial/pppd and serial communication. Those CDC ethernet USB dongles have web server and dhcp client.
What is the case with olimex dongle?
Tnx.

[dave-at-axon]

The issue for me with the Olimex USB units is import license restrictions where I need a license from the local telecommunications office before I can do so and then they have to be certified.

I have used local USB modems from Huawei that have been nice and stable for some time now, even 24/7 GPRS use.

I am working on a replacement though that will offer more free air around it to keep it cooler but using the same module so I can keep it certified. I am basically going to rehouse it in a larger plastic enclosure. There is no modification to the module PCB and I am hoping that certification is easier this way.

If I could find a ready to go industrial GPRS module I would go with that instead but none of them offer anything more than 384Kbps whereas the USB sticks are all 7.1Mbps.