redmi 2 is dual 4G dual standby @ LTE cat 4 150Mbps/50Mbps

from mi official websites :

4G Dual SIM. Up to 150Mbps download speeds.
Let your worlds collide with 4G dual SIM, dual standby. You won't have to manually switch SIM cards around with 4G support on both slots. Intelligent dual SIM features allow you to manage calls and messages easily, according to preferred network and data settings for each card. For instance, Redmi 2 allows you to create custom SIM labels so you don’t get mixed up. It also automatically selects which SIM to use when you call or text someone based on history.More about networks supported .

That is dual sim, dual stand by, single active. Piority given to voice call. Any sim make/recive call, data paused until end call.
Look for with Dual SIM, dual standby, dual active.

Sim A call Sim B and Sim B ringging