Similarly host, hub and terminal equipment are fundamental elements of the architecture as on USB interface based on standard 2.0. The main difference compared to USB in version 3.0 is the parallel connection of two physical buses, specifically USB 2.0 and new USB SuperSpeed.
It is satisfied to the requirement for backward compatibility by selecting of this architecture, because host and hub enable simultaneous operation of both physical buses through a mixed cables and connectors. Then the terminal equipment according to their capabilities uses either of the USB 2.0 or USB SuperSpeed.
Similarly the physical bus topology respectively tree structure is preserved, where is located in the root the host, which can be connected to a larger number of terminals or hubs.
The hubs can further provide connection to other terminal devices or other hubs.
Feature |
USB SuperSpeed |
USB 2.0 |
Data Channels |
two simplex – simultaneous bidirectional data flow, the two conductors on the direction (4 in total) |
poloduplex – unidirectional data flow with negotiating a change in direction, the two conductors |
Transfer Rate |
SuperSpeed – 5 Gbit/s |
according to mode 1,5 – 480 Mbit/s |
Transmission Protocol |
Asynchronous data flow driven by the host, packets routing |
the host allocates data rate (polling), packet broadcasting |
Power Management |
At the level of the connection, devices and functions, several states |
At the level of the connection and devices, only the Suspend state |
Bus Power Supply |
Like on USB 2.0, higher limits (50% for unconfigured devices and 80% for configured devices) |
Low and high power devices, the lower limit for unconfigured devices |
Each connection among the host and the devices (or the hubs) can be represented by communication layers. The following figure shows a diagram that describes each layer interconnection (see lines) and their elements in different parts of the topology (see left three columns) and the influence of power management (see right column).
USB 3.0 is a dual bus (Dual Bus Architecture), which is a parallel connection of USB 2.0 and the new USB SuperSpeed. This concept allows the usage of USB 2.0 terminal equipments on USB 3.0 controllers. However, there is one fundamental restriction. It is not possible to use both buses simultaneously at one terminal device.