CSFB with the Legba Lab Kit

Many 4G networks cannot carry plain old telephone calls, so many mobile operators support voice calls by transferring the handset to a 2G or 3G network for the duration of the call. The procedure for doing this is called “Circuit-Switched Fallback”, or CSFB. CSFB is an interesting procedure from a network operation perspective and from a security perspective. With a pair of Legba Lab Kits, one in 2G mode and one in 4G mode, you can reproduce and modify the CSFB procedure on a test bench.