USB4: What are the Advantages of USB 4.0?

What is USB4?

USB4 (aka: USB 4.0) is a specification by the USB Implementers Forum (USB-IF), which was released in version 1.0 on 29 August 2019. The USB4 protocol is based on the Thunderbolt 3 protocol; the Thunderbolt 3 specification was donated to the USB-IF by Intel Corp. The USB4 architecture can share a single high-speed link with multiple end-device types dynamically, best serving each transfer by data type and application.

In contrast to prior USB protocol standards, USB4 mandates the exclusive use of the Type-C connector, and mandates the use of USB PD for power delivery. USB4 products must support 20 Gbit/s throughput and can support 40 Gbit/s throughput, but due to tunnelling even nominal 20 Gbit/s can result in higher effective data rates in USB4, compared to USB 3.2 when sending mixed data. In contrast to USB 3.2, it allows tunnelling of DisplayPort and PCI Express.

Support of interoperability with Thunderbolt 3 products is required for USB4 hosts and USB4 peripheral devices, and is optional for USB4 hubs on their downward facing ports and for USB4-based docks on their downward and upward facing ports. On the other hand, support for USB4 is required in Thunderbolt 4.

The USB4 2.0 specification was released on October 18, 2022 by the USB Implementers Forum.

What are the Main Advantages of USB 4.0?

The new USB 4 standard has three main benefits over prior versions of USB.

• 40 Gbps Maximum Speed: By using two-lane cables, devices are able to operate at up to 40 Gbps, the same speed as Thunderbolt 3. The data is transmitted in two sets of four bidirectional lanes.
• DisplayPort Alt Mode 2.0: USB 4 supports DisplayPort 2.0 over its alternative mode. DisplayPort 2.0 can support 8K resolution at 60 Hz with HDR10 colour. DisplayPort 2.0 can use up to 80 Gbps, which is double the amount available to USB data, because it sends all the data in one direction (to the monitor) and can thus use all eight data lanes at once.
• Better Resource Allocation for Video, PCIe:  In lieu of alternative mode where the other interface takes over the connection, USB 4 devices can use a process called “protocol tunnelling” that sends DisplayPort, PCIe and USB packets at the same time while allocating bandwidth accordingly.
  
  So, if the video only needs 20 percent of the bandwidth to drive your 1080p monitor that’s also a hub, the other 80 percent will be free for transferring files from your external SSD which can operate over either USB protocol or PCIe.

USB4 Will Use Type-C Ports

USB 4 will only operate over the Type-C connector. Don’t expect to see a USB 4 device or hub with old-fashioned Type-A ports. That’s no surprise, as other recent standards such as USB Power Delivery only work on Type-C. If you do connect to, for example, a Type-A, 5 Gbps USB 3 port by using an adapter, the speed and power will drop down to the lowest common denominator.

USB4 Data Transfer Modes

USB4 by itself does not provide any generic data transfer mechanism or device classes like USB 3.x, but serves mostly as a way to tunnel other protocols like USB 3.2, DisplayPort, and optionally PCIe. While it does provide a native Host-to-Host protocol, as the name implies it is only available between two connected hosts; it is used to implement Host IP Networking. Therefore, when the host and device do not support optional PCIe tunnelling, the maximum non-display bandwidth is limited to USB 3.2 20 Gbit/s, while only USB 3.2 10 Gbit/s is mandatory.

USB4 specifies tunnelling of:

• USB 3.2 (“Enhanced Super speed”) Tunnelling
• DisplayPort 1.4a-based Tunnelling
• PCI Express (PCIe)-based Tunnelling

USB4 also requires support of DisplayPort Alternate Mode. That means, DP can be sent via USB4 tunnelling or by DP Alternate Mode.

DisplayPort Alt Mode 2.0: USB 4 supports DisplayPort 2.0 over its alternative mode. DisplayPort 2.0 can support 8K resolution at 60 Hz with HDR10 colour and can use up to 80 Gbit/s which is same amount available to USB data, but just unidirectional.

Legacy USB (1–2) is always supported using the dedicated wires in the USB-C connector.

Support of data transfer modes

Some transfer modes are supported by all USB4 devices, support for others is optional. The requirements for supported modes depend on the type of device.

Mode	Host	Hub	Peripheral device
Legacy USB (1–2) (max. 480 Mbit/s)	Yes	Yes	Yes
USB4 20 Gbit/s Transport	Yes	Yes	Optional
USB4 40 Gbit/s Transport	Optional	Yes	Optional
Tunnelled USB 3.2 (10 Gbit/s)	Yes	Yes	Yes
Tunnelled USB 3.2 (20 Gbit/s)	Optional	Optional	Optional
Tunnelled DisplayPort	Yes	Yes	Optional
Tunnelled PCI Express	Optional	Yes	Optional
Host-to-Host communications	Yes	Yes	–
DisplayPort Alternate Mode	Yes	Yes	Optional
Thunderbolt Alternate Mode	Optional	Yes	Optional
USB-C Alternate Modes	Optional	Optional	Optional

USB4 Power Delivery

USB4 requires USB Power Delivery (USB PD). A USB4 connection needs to negotiate a USB PD contract before being established. A USB4 source must at least provide 7.5 W (5 V, 1.5 A) per port. A USB4 sink must require less than 250 mA (default), 1.5 A, or 3 A @ 5 V of power (depending on USB-C resistor configuration) before USB PD negotiation. With USB PD, up to 240 W of power is possible with ‘Extended power range’ (5 A at 48 V). For ‘Standard Power range’ up to 100 W is possible (5 A at 20 V).

Thunderbolt 3 compatibility

The USB4 specification states that a design goal is to “Retain compatibility with existing ecosystem of USB and Thunderbolt products.” Compatibility with Thunderbolt 3 is required for USB4 hubs; it is optional for USB4 hosts and USB4 peripheral devices. Compatible products need to implement 40 Gbit/s mode, at least 15 W of supplied power, and the different clock; implementers need to sign the license agreement and register a Vendor ID with Intel.

USB4 Software Support

• Windows 11, released on 5 October 2021
• Linux kernel 5.6, released on 29 March 2020
• macOS Big Sur (11.0), released on 12 November 2020

USB4 Hardware Support

During CES 2020, USB-IF and Intel stated their intention to allow USB4 products that support all the optional functionality as Thunderbolt 4 products. The first products compatible with USB4 were Intel’s 11th generation Tiger Lake processors. In November 2020, Apple unveiled MacBook Air (M1, 2020), MacBook Pro (13-inch, M1, 2020), and Mac mini (M1, 2020) featuring two USB4 ports.

Products with USB4 Support

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