This read-only enumeration reports which cellular standard the WAN modem's radio operates on: cdma(1) for Code Division Multiple Access (3GPP-2) networks, or gsm(2), which per this MIB also covers 4G-LTE technology. An admin needs this to know which family of carrier-specific objects in this MIB (CDMA-branch vs. GSM/LTE-branch) actually applies to the installed modem, since CDMA and GSM devices report very different identifiers and metrics. For example, a router with a CDMA modem would report cdma(1) here, telling the admin to look at the c3gCdma* objects rather than the c3gGsm* ones for details like roaming status.