Full-duplex (FD) technology is under consideration for adoption in various legacy communications standards. The IEEE 802.11ax working group has been considering a simultaneous transmit and receive (STR) mode for the next-generation wireless local area networks (WLANs). Enabling STR mode (FD communication mode) in 802.11 networks creates bidirectional FD (BFD) and unidirectional FD (UFD) links. The key challenge is to integrate STR mode with minimal protocol modifications, while accounting for the coexistence of FD and legacy half-duplex (HD) stations (STAs) and backward compatibility. This paper proposes a simple and practical approach to enable STR mode in 802.11 networks while explicitly accounting for the peculiarities of BFD and UFD links along with the coexistence of FD and HD STAs. Key aspects of the proposed solution include FD capability discovery, handshake mechanism for channel access, node selection for UFD, adaptive acknowledgment timeout, and contention unfairness mitigation. A comprehensive analytical model has been developed to evaluate the gain of STR. Performance evaluation demonstrates the effectiveness of the proposed solution in realizing the gains of FD technology for next-generation WLANs.