We recently covered Circuit Switched fallback between LTE EUTRAN and GSM GERAN, and the SGs interface between the MME and the MSC.

One nifty feature of this interface is that you can send SMS using the MSC to switch the SMS traffic and the LTE/EUTRAN to transfer the messaging.

This means you don’t need Circuit Switched Fallback to send or receive SMS on LTE.

I assume this functionality was added to avoid the signalling load of constantly changing RAN technologies each time a subscriber sent or received an SMS, but I couldn’t find much about it’s history.

In order to get this to work you’ll essentially need the exact same setup I outlined in my CSFB example (Osmo-MSC, Osmo-STP, Osmo-HLR populated with the IMSI and MSISDN values you want to use for SMS), although you won’t actually need a GERAN / GSM radio network.

Once that’s in place you can just send SMS between subscribers,

Plus from the VTY terminal of OsmoMSC you can send SMS too:

OsmoMSC# subscriber msisdn 61487654321 sms sender msisdn 61412341234 send Hello World