Wireless USB
Certified Wireless USB ( CWUSB for short ) is a radio-based extension of the Universal Serial Bus standard and is intended to combine the security and speed of wired transmission with uncomplicated wireless transmission.
CWUSB is defined by the USB Implementers Forum. At the same time there is a specification for WUSB from Cypress Semiconductors , which has nothing to do with the version officially supported by the USB organization.
Availability
Two developments make it difficult for the devices to assert themselves in the market: On the one hand, the data throughput rate has been increased significantly with USB 3.0 , which increases the requirements for the wireless USB standard. On the other hand, the market development for smartphones has greatly expanded the spread of the Bluetooth standard. While the Bluetooth consortium is continuously developing its standard (most recently in 2016 with version 5), the last version of the USBCV tool for testing and developing wireless USB is dated July 17, 2009. Against this background, it is currently questionable whether CWUSB will once again gain in importance.
In August 2019, the corresponding WUSB driver of the Linux kernel was moved to the staging area. It should be completely removed in the medium term. This was justified with the non-availability of the corresponding hardware. The change took effect with Kernel Version 5.4.
properties
CWUSB is based on UWB ( OFDM ) technology (see also ECMA-368 ), which is defined by the WiMedia Alliance. Transfer rates of up to 480 Mbit / s are possible at a distance of up to 3 meters, this corresponds to the data transfer rate of USB 2.0. At a distance of 10 meters, the maximum transmission rate is 110 Mbit / s.
The transmission takes place in the frequency range between 3168 and 10560 MHz , which is divided into 14 bands with a bandwidth of 528 MHz. These bands are combined into 5 band groups. Band groups 1 to 4 are 3 bands wide (band group 1: band 1 + 2 + 3 = 3168-4752 MHz ... band group 4: band 10 + 11 + 12 = 7920-9504 MHz), band group 5 is only 2 Bands wide (band group 5: band 13 + 14 = 9504-10560 MHz). The first devices are expected for band group 1, although this frequency range has not yet been released worldwide for this technology. In the EU , however, according to the decision of the European Commission, only the frequency range 6000 to 8500 MHz will be released for this technology from 2010, which corresponds to band group 3 (band 7 + 8 + 9 = 6336-7920 MHz). In Germany, this already happened on January 16, 2008. At CeBIT 2008, some manufacturers presented the first WUSB devices.
In a new revision there will be a band group 6 (band 9 + 10 + 11 = 7392 ... 8976 MHz), which is in the range of band groups 3 and 4. These tapes are available worldwide without any restrictions. Mobile telephones will probably use band group 3 or 6, because band group 1 creates mutual interference with UMTS / GSM / BT. This would mean that these devices would be incompatible with the first devices delivered that only support tape group 1.
roll
In CWUSB, like in USB, there is a host that can serve up to 127 end devices. The host determines at any point in time when an individual device may send something. The host uses the functions provided by a device; for example, a mass storage device (MSC) provides the host with functions for read and write access to a memory.
A CWUSB device can be a simple device, a host or a so-called dual role device. A dual role device can assume the role of both a host and a device.
topology
The connection between the host and the end device is a point-to-point connection . A network consisting of a host and the connected end devices is called a cluster. End devices can only exchange data with the host, but not directly with other end devices in the cluster.
safety
Before connecting an end device to a host for the first time, the connection must be allowed and authorized. There are two ways to do this:
- In the association with user control , a common key is agreed by means of a four-way handshake without sending it over the medium. To do this, the host sends a random number H to the terminal, which replies with a random number D. A common key is now calculated from H, D and the terminal addresses using a CBC - MAC one-way function.
Since this method is prone to man-in-the-middle attack , the user must check the host display and the terminal display to ensure that the numbers shown are the same. If this is the case and the user confirms this, the connection is considered secure and can be used. - With the out-of-band association , a wired USB connection is used to authorize the wireless connection by transmitting some data (encryption key, device identifier, host identifier, friendly names, supported UWB bands, etc.). No further entries are then required when establishing the CWUSB connection. Alternatively, the key can also be displayed or printed on the terminal and entered by the user on the host.
Authentication is only necessary once. When a connection is established, the data is always encrypted ( AES-128 - CCM encryption) if the host has assigned an address to the USB device.
Migration of USB devices to CWUSB
Normal USB devices can easily be ported to CWUSB technology by connecting USB end devices to a Device Wire Adapter (DWA) and a USB host to a Host Wire Adapter (HWA). The USB terminal recognizes the DWA as a USB host and the host sees the HWA as a terminal. One or more DWAs are wirelessly connected to an HWA via CWUSB. Wired adapters (WA) thus serve as a bridge between wireless and wired technology.
Web links
- Information on WUSB at TecChannel
- CWUSB Information from the USB Implementers Forum (English)
- ECMA documents, especially ECMA-368 and ECMA-369 (English)
- WiMedia Alliance (English)
- Wireless USB News (English)
swell
- ↑ kernel / git / torvalds / linux.git - Linux kernel source tree. Retrieved November 25, 2019 .
- ↑ Frequencies made available for ultra-wideband technology ( memento of the original from September 19, 2009 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , Federal Network Agency, January 16, 2008 (PDF)
- ↑ General allocation of frequencies for use by low-power applications of Ultra-Wideband (UWB) technology ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. , Federal Network Agency (PDF)
- ↑ Wireless USB - Put an end to the cable clutter ( Memento of the original from March 13, 2008 in the Internet Archive ) Info: The archive link was inserted automatically and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. , CeBIT trend spot 2008
