USB4 mainly has two applications: USB4 host and USB4 device. USB4 devices are further divided into USB4 external devices, USB4 hubs and USB4 docking stations.
USB4 host applications mainly include laptops, game consoles, etc. USB4 devices can be mobile hard drives, hubs, docking stations, etc. The image below shows the connections for a USB4 host, USB4 hub, and USB4 external device.
1. USB4 host
The USB4 host consists of: a host router, an internal controller and a DisplayPort source. The USB4 host must support the operation of USB4 Gen2x2 with a bandwidth of 20Gbps. The USB4 Gen3x2 with a bandwidth of 40Gbps is optional and may or may not be supported.
The USB4 host needs to support DisplayPort configuration in the USB PD protocol.
Note: The router here refers to a structure that selects the best signal transmission path, not the router we commonly use for splitting wifi.
2. USB4 device
2.1. USB4 external devices
USB4 external devices only have a separate upstream port (Upstream Facing Port) and no downstream port (Dowmstream Facing Port).
USB4 external devices include a device router. May include one or more of the following:
An Enhanced SuperSpeed hub or endpoint (the destination to which USB data is received or the source to which it is sent)
A PCIe switch or endpoint (the destination to which PCIe data is received or the source to which PCIe data is sent)
A DisplayPort source or sink
Note: The upstream port refers to the receiver of data, and the downstream port refers to the sender of data. This definition applies to USB ports and PCIe ports.
2.2. USB4 hub
A USB4 hub consists of an upstream port and multiple downstream ports, and is mainly used for port expansion.
The downstream port (Downstream Facing Port) of the USB4 hub can support USB 3.2 and USB 2.0, that is, USB4 has backward compatibility.
The USB4 hub consists of a DisplayPort source or receiver, device router, enhanced superspeed USB hub, PCIe switch, and USB 2.0 hub.
USB4 hub supports 20G USB4 operation (Gen2x2) and 40G USB4 operation (Gen3x2).
The USB4 hub needs to support DisplayPort configuration in the USB PD protocol.
Note: PCIe switch refers to the structure in which one uplink port and multiple downlink ports are connected in PCIe.
In addition to one upstream port and multiple downstream ports, the USB4 docking station also has a port for external device functions. The requirements for a hub also apply to a docking station, but the difference is that the docking station has an additional port for peripheral functions.
