SMS on 4G only network on RUT200 with no data connection

Networking Solutions Question
1

Hi,

I have a RUT200 with a mobile SIM card for our Swiss operators that have shutdown all 2G/3G networks so in Switzerland you’re left with 4G/5G only and have to use that to send SMS.

In addition I have a prepaid card that charges 2Fr. a day flat whenever there is even the smallest data transfer over the mobile network connection.

I have already found the knowledge base article about denying network access to clients but it’s quite outdated most cli commands don’t work any longer as there’s no ppp network or so. Another killer command on 4G is to disable it via SMS. What worked: mobileoff. But don’t expect to be able to turn it on again with mobileon as this also kills the entiren SMS functionality completely on 4G. No incoming, no ougoing sms. Took me quite a while to get it working again.

So my question is: does sending SMS on a 4G network always need a data connection? If so, how can I forbid (as I said FAQ is outdated) that not a single byte of data is sent to the mobile connection not to trigger the 2Fr./flat payment every day as I don’t need it as a router. I need a dumb LAN Client SMS Gateway (no routing functionality).

What I already did:

  • re-purposed the WAN port as the port connecting to the internal network and getting a DHCPv4 & DHCPv6. I first tried to use the LAN port which sounds like it’s the go-to port but LAN network in UI don’t support protocol “DHCP”, only WAN networks do (and I didn’t want to mess around with uci commands making it incompatible with WebUI).
  • changed the network of the mobile connection to be in a zone (not wan) but “dummy” as the only device.
  • created a new LAN connection to be used with access point functionality as a safeguard if my LAN connection dies by misconfiguration.

So, what I’m really stuck with is as stated before: disable a single data connection byte being sent over the 4G mobile connection except incoming & outgoing SMS as transferred data immediately triggers a flat mobile data fee every 24hrs. Which quickly eats up the prepay credits.

Any help on what really works on the RUT200 would be great.

Thanks in advance

2

Hello @marcelser

I successfully use a prepaid SIM in a phone for SMS (and voice) only, with mobile data turned off all the time. Are you sure mobile data is required for SMS? Maybe you could turn off / block mobile data on the provider side? Assuming you are using a Swisscom prepaid SIM, maybe this post helps.

Thanks

Felix

3

Phones are different then the RU200, they are probably idiot proof. Means if they need a data connection they keep it open in background without showing they real under the hood operations. As to the question if you need a data connection for SMS it seems on a 4G you need it, but when I turn it off sms stops working. You might get away if you’re on a mobile operator that still supports 3G network but in Switzerland all 2G and all 3G networks have been shut down. And yes it’s a swisscom Sim card.

4

Hello @marcelser

I agree there are differences between a router (data only) and a mobile phone (voice/data) - I’ve seen that myself before.

That said, I am using a Swisscom Prepaid SIM card in Switzerland (so no 2G/3G anymore), mobile data on the phone is turned off and ‘basic tariff’ is deactivated in Swisscom cockpit, yet SMS still works and voice still works using VoLTE. The phone is registered on 4G.

The modem in RUT200 seems to be a Quectel EC200A-EU which according to its datasheet supports voice (VoLTE) as well, e.g. it’s not a data only modem. So I wonder as to why SMS stops working for you when data is turned off.

Just curious: did you turn off data in RUT200 and/or in the Swisscom cockpit?

Thanks

Felix

5

Hello @marcelser,

Could you kindly confirm whether the issue has been resolved, or if you still require any assistance?

Best regards,

6

Since I have put the mobile connection into its own zone as the only device it works. But disabling data connection itself kills SMS functionality on 4G only networks. So for my case it works and it’s solved