USB 3.1: What’s in a Name?
By Morten Christiansen, Technical Marketing Manager, USB IP
Clarity around names and nomenclature enable effective communication about a topic. Standards bodies define the nomenclature for their standards and specifications, and engineers and designers use what makes sense for them, often generating nicknames as well. Long term, the ecosystem around a standard will coalesce and use the most effective terminology. This article describes the USB 3.1 terminology as defined in the USB-IF specification to give designers and users a starting point for understanding the wide range of applicable USB terms.
The USB 3.0 specification is also known as the SuperSpeed USB specification. The SuperSpeed USB specification introduced a subtle change in spelling compared to the previous USB speeds. They are now officially named “low-speed,” “full-speed,” and “high-speed,” and are often abbreviated to LS, FS, and HS.
The inappropriate use of names and terminology can cause considerable confusion and grievance. For example, when USB designers use the term “BC,” you can assume the discussion relates to the USB-IF Battery Charging specification, version. 1.2. However “BC” could also refer to EN 62684:2010, IEC 62684:2011, or ITU TL.1000 which are all based on the USB-IF Battery Charging specification version 1.1. CCSA YD/T1591 2006, yet another BC specification, actually refers to a prerelease version (0.77) of the original USB-IF battery Charging specification that was officially released as version 1.0 in 2007.
The USB 3.1 specification supersedes the USB 3.0 specification and had to accurately describe the USB 3.0 or legacy SuperSpeed features, the new USB 3.1 features, and generic features. Of vital importance is backwards compatibility between devices, hubs and hosts built to the USB 3.0 specification and the new USB 3.1 specification. All combinations of old and new hosts, hubs and devices operating in any mode must be accurately described with the new nomenclature.
The new nomenclature has to be both accurate and efficient (Figure 1).
The term Enhanced SuperSpeed system is used to describe the any combination of a device/host, protocol layer, link layer, and physical layer that adheres to the USB 3.1 specification.
At the electrical or physical level, PHYs operate in Gen 1 or Gen 2 mode. Gen 1 uses the 5 Gbps signaling rate described in the USB 3.0 specification. Gen 2 uses a new 10 Gbps signaling rate described in the USB 3.1 specification.
SuperSpeed USB is used to describe the legacy link, protocol and host/device controllers at the architecture or system abstraction level for Gen 1 operation. The term SuperSpeedPlus USB is used to describe the new link, protocol and controller operation for Gen 2.