The main controller is responsible for the transmission of data flow between host and line to board connector equipment. These transmission data are treated as successive bit streams. Each device is provided with one or more interfaces that can communicate with the client program. Each interface is composed of 0 or more pipelines, which transmit data between the client program and the specific terminal of the device when they log on alone. The line to board connector D establishes an interface and pipeline for the actual needs of the host software. When an equipment request is made, the main controller provides services according to the parameters provided by the host software.

The line to board connector supports four basic data transmission modes: manipulation transmission, isochronous transmission, abort transmission and data block transmission. Each transmission mode has different properties when applied to terminals with the same name.

Isochronous transmission type (or synchronous transmission) supports data transmission between peripherals and hosts with periodic, limited delay and bandwidth and constant data transmission rate. This type of error free verification can not ensure accurate data transmission and support data transmission between computer telephone integrated system (CTI) and audio system and host.

The interrupt transmission type supports input devices such as joystick, mouse and keyboard. The data transmission volume between these devices and the host is small and non periodic, but they are sensitive to the echo time and request immediate echo.

The data block transmission type supports peripherals such as printers, scanners and digital cameras. The amount of data transmitted between these peripherals and the host is large, and the line to board connector can only transmit this type of data when the bandwidth is satisfactory.

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

The line to board connector adopts the block bandwidth allocation plan. If the peripheral exceeds the current bandwidth allocation or potential request, it cannot enter the device. Terminals that synchronize and abort transmission types save bandwidth and ensure that data is transmitted at a certain rate. The centralized and control terminal transmits data according to the best available bandwidth.