If the device can simultaneously handle both directions (such as uploading, downloading) the data transfer, the data transmission is full duplex. A half-duplex connection the same time transmit data in one direction only. Think about radio transceiver, you can only hear each other when not transmitted speech. SuperSpeed ​​bus uses two pairs because different lines transmit data, it can transfer data in both directions simultaneously, namely full-duplex, rather than USB 2.0 .