USB block transmission in veterinary B-ultrasound system, also known as batch transmission, has the characteristics of large data transmission volume and no requirements for transmission time and transmission rate. When the bandwidth of USB bus in veterinary B-ultrasound system tends to be tight, block transmission is used for data transmission. The data transmission rate is generally very low and the required transmission time is also very long. This is because in order to leave bandwidth for other transmission types, block transmission automatically delays its own transmission; on the contrary, when the bandwidth of USB bus in veterinary B-ultrasound system is idle, the data transmission rate of block transmission will be very high and the required time will be very short. The characteristic of block transmission that automatically adjusts the occupied bandwidth time ensures that the USB bus in veterinary B-ultrasound system will not be blocked while transmitting data. However, when the bandwidth of USB bus in veterinary B-ultrasound system is tight, the transmission time and transmission rate of block transmission cannot be well guaranteed. In addition, in order to ensure the correctness of the transmitted data, block transmission enables two mechanisms, retry and error control, during the transmission process. Because block transmission has the above characteristics, it is usually used in devices such as printers and scanners, because for devices such as printers, the data transmission rate is obviously not as important as the error-free sending and receiving of data.

USB block transfer in veterinary B-ultrasound system is generally used on high-speed or full-speed USB devices, but these devices may not support this data transmission method. Veterinary B-ultrasound system generally needs to include three stages for USB block transfer: token, data and handshake, but in some special cases, such as endpoints being stopped or data transmission errors, the data stage can be replaced by the handshake stage, that is, only two stages or one stage (token stage) are used to process block transfer transactions. The transaction processing of USB block transfer in veterinary B-ultrasound system is unidirectional, either IN or OUT.