3.0 is the third major version of the Universal Serial Bus (USB) standard for interfacing computers and electronic devices. Among other improvements, USB 3.0 adds the new transfer rate referred to as SuperSpeed USB (SS) that can transfer data at up to 5 Gbit/s (625 MB/s), which is about 10 times faster than the USB 2.0 standard. It is recommended that manufacturers distinguish USB 3.0 connectors from their USB 2.0 counterparts by using blue (Pantone 300C) for the Standard-A receptacles and plugs, and by the initials SS. USB 3.1, released in July 2013, is the successor standard that replaces the USB 3.0 standard. USB 3.1 preserves the existing SuperSpeed transfer rate, giving it the new label USB 3.1 Gen 1, while defining a new SuperSpeed+ transfer mode, called USB 3.1 Gen 2 which can transfer data at up to 10 Gbit/s over the existing USB-type-A and USB-C connectors (1250 MB/s, twice the rate of USB 3.0). USB 3.2, released in September 2017, replaces the USB 3.1 standard. It preserves existing USB 3.1 SuperSpeed and SuperSpeed+ data modes and introduces two new SuperSpeed+transfer modes over the USB-C connector using two-lane operation, with data rates of 10 and 20 Gbit/s (1250 and 2500 MB/s). Protocol Each hub has exactly one upstream port and a number of downstream ports. The upstream port connects the hub (directly or via other hubs) to the host. Other hubs or devices can be attached to the downstream ports. During normal transmission, hubs are essentially transparent: data received from its upstream port is broadcast to all devices attached to its downstream ports (pictorially described in the USB 2.0 specification in Figure 11–2, Hub Signalling Connectivity). Data received from a downstream port is generally forwarded to the upstream port only. This way, what is sent by the host is received by all hubs and devices, and what is sent by a device is received by the host but not by the other devices (an exception is resume signalling). Downstream routing has been changed in USB 3.0 with the addition of Point to Point routing: A route string sent in the packet header allows a USB 3.0 host to only send a downstream packet to a single destination port, decreasing congestion and power consumption. Hubs are not transparent when dealing with changes in the status of downstream ports, such as insertion or removal of devices. In particular, if a downstream