Communication apparatus includes a transceiver configured to transmit and receive signals over a wireless channel in accordance with both a first communication protocol and a second communication protocol, the second communication protocol being backward-compatible with the first communication protocol. The transceiver is configured to provide capabilities that are supported by the second communication protocol but are not supported by the first communication protocol. A communication controller is configured to generate data frames for transmission by the transceiver. The date frames include frame headers that are compatible with the first communication protocol while including, in a specified field of the frame headers, a predefined value indicating that the apparatus is capable of communicating in accordance with the second communication protocol.