USB 3.0-The advanced data transfer

INTRODUCTION

• USB 3.0 is the third major version of the Universal Serial Bus (USB) standard for interfacing computers and electronic devices.
• USB 3.0 adds the new transfer rate referred to as Super Speed USB (SS) that can transfer data at up to 5 Gbit/s (625 MB/s), which is about ten times as fast as the USB 2.0 standard.
• Manufacturers are recommended to distinguish USB 3.0 connectors from their USB 2.0 counterparts by blue color-coding of the Standard-A receptacles and plugs, and by the initials SS.
• The SuperSpeed transaction is initiated by the host making a request followed by a response from the device. 
• The device either accepts the request or rejects it; if accepted, the device sends data or accepts data from the host. 
• If the endpoint is halted, the device shall respond with a STALL handshake.
• If there is lack of buffer space or data, it responds with a Not Ready (NRDY) signal to tell the host that it is not able to process the request. 
• When the device is ready, it will send an Endpoint Ready (ERDY) to the host which will then reschedule the transaction

• The specification of USB 3.0 is similar to that of USB 2.0, but with many improvements and an alternative implementation. 
• Earlier USB concepts such as endpoints and the four transfer types (bulk, control, isochronous and interrupt) are preserved but the protocol and electrical interface are different.
• The specification defines a physically separate channel to carry USB 3.0 traffic. The changes in this specification make improvements in the following areas

IMPROVEMENTS

• Transfer speed – USB 3.0 adds a new transfer type called SuperSpeed or SS, 5 Gbit/s Increased bandwidth – instead of one-way communication, USB 3.0 uses two unidirectional data paths: one to receive data and the other to transmit
• Power management – U0 to U3 link power management states are defined
• Improved bus use – a new feature is added (using packets NRDY and ERDY) to let a device asynchronously notify the host of its readiness, with no need for polling
• Support to rotating media – the bulk protocol is updated with a new feature called Stream Protocol that allows a large number of logical streams within an Endpoint
• USB 3.0 has transmission speeds of up to 5 Gbit/s, which is about ten times faster than USB 2.0 (480 Mbit/s) even before taking into account the fact that USB 3.0 is full duplex whereas USB 2.0 is half duplex. 
• This gives USB 3.0 a potential total bandwidth, if used both ways, of twenty times that of USB 2.0

USB 3.1

• USB 3.1, released in July 2013, is the successor standard that replaces the USB 3.0.
• Its now called USB 3.1 Gen 1, while defining a new transfer rate called SuperSpeed USB 10 Gbps, also called USB 3.1 Gen 2, which can transfer data at up to 10 Gbit/s (1.25 GB/s, twice the rate of USB 3.0),maximum transfer speed is far above thaanThunderbolt interface.
•  The USB 3.1 standard increases the maximum data signaling rate to 10 Gbit/s (1250 MB/s), double that of SuperSpeed USB, and reduces line encoding overhead to just 3% by changing the encoding scheme to 128b/132b. 
• The first USB 3.1 implementation demonstrated real-world transfer speeds of 7.2 Gbit/s.
• The USB 3.1 standard is backward compatible with USB 3.0 and USB 2.0.
• USB 3.1 Gen 1, USB 3.1 Gen 1 has the same 5 Gbit/s SuperSpeed maximum data signaling rate as USB 3.0.
• USB 3.1 Gen 2, USB 3.1 Gen 2 has a new 10 Gbit/s (1250 MB/s) SuperSpeed+ maximum data signaling rate—double that of USB 3.0.

USB 3.2

• On 25 July 2017, a press release from the USB 3.0 Promoter Group detailed a pending update to the USB Type-C specification, defining the doubling of bandwidth for existing USB-C cables. 
• Under the USB 3.2 specification, existing SuperSpeed certified USB-C 3.1 Gen 1 cables will be able to operate at 10 Gbit/s (up from 5 Gbit/s), and SuperSpeed+ certified USB-C 3.1 Gen 2 cables will be able to operate at 20 Gbit/s (up from 10 Gbit/s). 
• The increase in bandwidth is a result of multi-lane operation