Wi-Fi Direct

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Wi-Fi Direct is a standard for data transfer between two WLAN end devices without a central wireless access point . Wi-Fi Direct is based on the international standard IEEE 802.11 (ISO / IEC 8802-11), which describes the properties of a wireless network. Wi-Fi Direct capable devices are certified by the Wi-Fi Alliance ; this ensures that interoperability is guaranteed at least between Wi-Fi certified devices.

background

Products that want to come onto the market as Wi-Fi Direct-enabled must be certified by the Wi-Fi Alliance. The consortium has existed since 1999 and aims to ensure the interoperability of devices that are approved under the IEEE 802.11 standard. We test using our own guidelines. Devices that pass the test are marked with the “Wi-Fi Certified” logo.

Technical functionality

The special thing about Wi-Fi Direct-enabled devices is that they can communicate with each other directly. Instead of using cables, for example, the data is transmitted from a computer to a smartphone or from a digital camera to a printer in the ISM bands around 2.4 GHz or 5.8 GHz. In contrast to a conventional WLAN, neither an access point nor a hot spot are required for data transmission - the Wi-Fi-enabled devices themselves function as a base station.

For this functionality, devices with Wi-Fi Direct capability are equipped with a “software access point”. This can be used to detect other WLAN or Wi-Fi-enabled devices in the vicinity. Using various protocols - Universal Plug and Play (UPnP), Devices Profile for Web Services (DPWS) and Apple's Bonjour software - Wi-Fi Direct-enabled end devices identify other devices that can communicate with them ad hoc. These do not necessarily have to support Wi-Fi Direct as well; it is sufficient if these devices are WLAN-capable and compatible with the 802.11 standard.

Wi-Fi Direct can be used to connect two devices as well as entire groups of devices. The installation of a Wi-Fi network should be kept simple for the user and is carried out via the Wi-Fi Protected Setup (WPS).

The Wi-Fi Protected Setup can be done in different ways:

  • PIN : Enter a PIN on the access point .
  • Push button: The user must press a - real or virtual - button on both the access point and the Wi-Fi-enabled device.
  • NFC : With this method, it is sufficient to bring the new Wi-Fi-enabled device close to the access point.
  • USB : Data for setting up the network between the new terminal device and the access point are transferred via USB.

Function from the user's point of view

In the Wi-Fi Direct specification, only the technical functionality is standardized across manufacturers, i.e. the three tasks of finding each other, authenticating and transmitting data - but the specification does not contain any requirements for a uniform user interface. The result is that even if devices comply with the Wi-Fi Direct standard in terms of hardware technology, they still cannot connect to one another because, for various reasons, the user interface of the program or operating system only shows certain devices for connection selection.

application areas

Virtually any digital end device can function as a Wi-Fi Direct capable access point. The importance of the 802.11 standard has increased with the spread of smartphones. The data transfer from the smartphone to the computer and vice versa is uncomplicated and wireless via Wi-Fi Direct. It is also possible to send data from a computer to a printer on the network via Wi-Fi Direct or from a digital camera to a printer or a digital picture frame.

Wi-Fi Direct generations

There are now different generations of Wi-Fi Direct. All are approved according to the 802.11 standard and are further identified with a letter. The current generation since September 2010 is called 802.11g. It is downward compatible with the older generations, provided they operate on the same frequency. A device that is approved according to the 802.11g standard can therefore also communicate with a device of the 802.11b generation.

The expanded standards are either characterized by improved transmission rates or introduce expanded security and interoperability standards. The most widely used standard to date is 802.11b, which transmits on a frequency of 2.4 GHz on three radio channels. The standards 802.11a, 802.11b, 802.11g and 802.11n are relevant for the end user. The other standards do not bring any relevant innovations for end users, but define the Wi-Fi standard more precisely.

Bandwidths and range

In the open air it should be possible to bridge up to 500 meters without an additional antenna and without an amplifier, indoors at least up to 90 meters - but walls and ceilings also weaken the Wi-Fi signal.

The data rate depends on the physical distance between the respective devices: the greater the distance between the Wi-Fi Direct-enabled devices, the lower the bandwidth with which data transmission is possible. The range of devices with Wi-Fi standard 802.11g is around 10 meters indoors with a bandwidth of 54 Mbps (megabits per second max. Gross data rate), but already 70 meters with a bandwidth of 6 Mbps.

safety

Data security is a sensitive issue in radio transmission. The Wi-Fi Alliance has been certifying the Wi-Fi Protected Access (WPA) encryption method since 2003 in order to increase the security of the Wi-Fi network. This standard replaced the WEP , which was used until then, but was considered unsafe . For most devices, only the factory safety measures are active at the time of delivery. When starting up the device, at the latest when configuring a Wi-Fi network, the device should be given a new user name if possible, but in any case a new password.

Web links

Individual evidence

  1. ↑ wi-fi.org ( Wi-Fi Alliance ): "Discover Wi-Fi - Wi-Fi Direct" ( Memento from October 7, 2019 in the Internet Archive )
  2. ↑ wi-fi.org: Wi-Fi Protected Setup ™ ( Memento from February 8, 2008 in the Internet Archive )
  3. ↑ a b Dušan Živadinović: “WLAN without a router. Ad-hoc file transfer and repeater function with WiFi Direct “ ( Memento from 7 December 2019 in the Internet Archive ) in: c't 2016 issue 6, pages 100-104.
  4. ↑ ccm.net (originally kioskea.net): Introduction to Wi-Fi (802.11) ( Memento from December 7, 2019 in the Internet Archive )