Wireless USB
The standard is now obsolete, and no new hardware has been produced for many years though it has been adopted by Android for precise signaling [1] Support for the standard was deprecated in Linux 5.4[2][3] and removed in Linux 5.7[4] The rationale for this specification was the overwhelming success of USB as a base for peripherals everywhere; cited reasons include extreme ease of use and low cost, which allow the existence of a ubiquitous bidirectional, fast port architecture.
The goal of the specification was to preserve the functional model of USB, based on intelligent hosts and behaviorally simple devices, while allowing it to operate in a wireless environment and keeping security on a par with the levels offered by traditional wired systems.
W-USB was defined as a bus, albeit logical and not physical, which can simultaneously connect a host with a number of peripherals.
[citation needed] It was also suitable for transferring parallel video streams, using USB over ultra-wideband protocols.
Around the same time, Belkin, Dell, Lenovo, and D-Link began shipping products that incorporated WiQuest technology.
A small, but significant, number of former WiMedia members had not and would not sign up to the necessary agreements for the intellectual property transfer.
As mentioned, the USB model is preserved, and generally minor adjustments made to fit the specific needs of a wireless system.
The changes are as follows, from top to bottom: The replacement of copper wires in the bus layer introduces ambiguity in the actual state of host-device connections and, even more importantly, potentially exposes communications fully to any other device within the propagation range, whereas they were reasonably secure over the wire.
Flow control and packet sizes are adjusted for power efficiency, while respecting the high-level pipe model of communication between source and destination.
On their end, hosts manage global timers with the precision the physical medium requires (20 ppm).
This is related to the transaction group concept, which consists of a microscheduled management command (MMC) and allocated time slots for the execution of its associated workload.
The fact that the communications protocol is based on TDMA means that both host and devices know exactly when their presence is not required, and can use this to enter power saving modes.
For example, a digital camera could act as a device when connected to a computer and as a host when transferring pictures directly to a printer.
It implements the USB hub–spoke model, in which up to 127 wireless devices can form point-to-point links (spokes) with the host (the hub).
Even though the physical layer is based on Ultra-WideBand, W-USB devices have a fully compliant USB interface.
UWB is a general term for radio communication using pulses of energy which spread emitted Radio Frequency energy over 500 MHz+ of spectrum or exceeding 20% fractional bandwidth within the frequency range of 3.1 GHz to 10.6 GHz as defined by the FCC ruling issued for UWB in February 2002.
WUSB was a protocol promulgated by the USB Implementers Forum that used WiMedia's UWB radio platform.
Packet loss and corruption are dealt with through timeouts as well as hardware buffering, guaranteed retries (as mentioned in the description of transfer models) and other flow control methods.
The W-USB host tries to mitigate the unreliability of wireless mediums (a 10% error rate is considered acceptable for 1 kB packets; in wired media this value is usually around 10−9) maintaining counters and statistics for each device and possible requesting information from them.
It can also access and modify the transmit power control functions of each device, as well as change transmission parameters such as data payload size and bandwidth adjustments.
Wires offer a very high level of security (given a typical trusted working environment), so standard USB does not deal with it, even though it does not hinder its applicability or implementability; W-USB manages security explicitly, but instead of harnessing the base of UWB it designs a model which is valid for USB in general.
These must have a defined purpose and restrict membership to the group, which serves as the base of trust to carry out the desired work.
Within a wired systems, data transfers imply a controlled physical connection; this translates into the wireless domain through the concept of ownership: the user grants trust to the devices, which in turn prove this trust to others (interacting in so-called ceremonies) in order to form the desired associations.
Applications may require other bases of trust not directly supported by this USB-specific model, in which case they can be implemented on top of the core USB stack.
After receiving the group key of a cluster, a device must keep the connection alive by at least confirming its presence within each trust timeout boundary, which is set to four seconds.
It is also important to note that replay prevention mechanisms require the keeping of counters which are updated on valid receptions.
The result was that the name Certified Wireless USB was adopted to allow consumers to identify which products would be adherent to the standard and would support the correct protocol and data rates.
[21] The protocol is being developed from the base of the Wi-Fi Alliance's previous WiGig Serial Extension specification.
