System and method for low-overhead interoperability between 4G and 5G networks

Techniques described herein may allow for the seamless and efficient use of multiple radio access technologies ("RATs"), such as 4G and 5G RATs. A virtualized base station may be used, which processes traffic sent to and/or received from a user equipment ("UE") via 4G and 5G RATs. The virtualized base station may include separate protocol stacks for the separate RATs. One RAT may be the "master" RAT, and the protocol stack for the master RAT may communicate with a core network via a General Packet Radio ("GPRS") Tunneling Protocol ("GTP") tunnel. In the downlink direction, the virtual base station may determine via which RAT traffic, received from the core network, should be sent to the UE by identifying quality of service class indicators ("QCIs") associated with the downlink traffic.