The main controller serves as the transmission of data flow between the host and USB devices. These transmitted data are treated as contiguous bitstreams. Each device provides one or more interfaces that can communicate with the client program, each interface consisting of 0 or more pipelines that independently transmit data between the client program and specific terminals of the device. USB establishes interfaces and pipelines for the actual requirements of the host software. When equipment requests are made, the main controller provides services based on the parameters provided by the host software.

USB supports four basic data transmission modes: control transmission, isochronous transmission, suspend transmission, and data block transmission. Each transmission mode has different properties when applied to terminals with the same name.

The control transmission type supports the transmission of control, condition, equipment, and other information between peripherals and hosts, providing a control channel between peripherals and hosts. Each peripheral supports the type of control transmission, so that equipment and command/condition information can be transmitted between the host and the peripheral.

The isochronous transmission type (also known as synchronous transmission) supports data transmission between peripherals and hosts with periodicity, limited latency and bandwidth, and constant data transmission rate. This type of error free verification cannot ensure correct data transmission, supporting data transmission between computer telephone integrated systems (CTI) and audio systems and the host.

Abort transmission type supports input devices such as game controllers, mice, and keyboards. These devices have a small amount of data transmission between the host and the host, without periodicity, but are sensitive to response time and require immediate response.

The data block transmission type supports peripherals such as printers, scanners, and digital cameras. These peripherals transmit a large amount of data to the host, and the USB only performs this type of data transmission when the bandwidth is satisfactory.

USB adopts a segmented bandwidth allocation scheme, and if the peripheral exceeds the bandwidth allocation or potential requirements at that time, it cannot enter the device. Synchronize and suspend transmission type terminals to retain bandwidth and ensure data transmission at a certain rate. Centralize and control terminals to transmit data according to the best available bandwidth.