• Wi-Fi Direct allows direct connections without an AP. Source: Kaushal D 2016.
    image
  • Wi-Fi Direct can used in 1:1 or 1:n configurations. Source: RF Wireless World 2018.
    image
  • P2P Group Owner can also connect to AP while managing the group. Source: Devopedia.
    image

Wi-Fi Direct

Improve this article. Show messages.

Summary

image
Wi-Fi Direct allows direct connections without an AP. Source: Kaushal D 2016.

Wi-Fi-Direct is a standard developed by Wi-Fi Alliance so that Wi-Fi devices can connect and communicate with each other directly without using an access point (AP). This is also known as Wi-Fi P2P (Wi-Fi Point-to-Point). This is very useful for direct file transfer, internet sharing, or connecting to a printer. Wi-Fi Direct can communicate with one or more devices simultaneously at typical Wi-Fi speeds.

Wi-Fi Direct supports IEEE 802.11 a/b/g/n/ standards.

Milestones

Oct
2010

Wi-Fi Alliance launches Wi-Fi Direct certification program. Meanwhile, Atheros, Broadcom, Intel, Ralink and Realtek announce their first products.

Oct
2011

Google announces Wi-Fi Direct support in Android 4.0.

Mar
2016

Sony, LG, Philips and X.VISION implement Wi-Fi Direct on some of their televisions.

Discussion

  • Can you explain how Wi-Fi Direct works?

    Wi-Fi Direct works in two steps:

    • 1. Device Discovery: A device first broadcasts a probe request message asking for MAC ID from all nearby devices. This stage is similar to the scanning phase in regular Wi-Fi. All devices that hear this message respond with a unicast message to the sender.
    • 2. Service Discovery: Now the sender sends a unicast service request message to each device. The receiving devices responds with unicast message with service details.
  • How many devices can Wi-Fi Direct connect?

    A Wi-Fi Direct-certified network can be one-to-one, or one-to-many. The number of devices in a Wi-Fi Direct-certified group network is expected to be smaller than the number supported by traditional standalone access points intended for consumer use. Connection to multiple other devices is an optional feature that will not be supported in all Wi-Fi Direct-certified devices; some devices will only make 1:1 connections.

  • Can you explain architecture of Wi-Fi Direct?
    image
    Wi-Fi Direct can used in 1:1 or 1:n configurations. Source: RF Wireless World 2018.

    As Wi-Fi Direct does not require any AP, the device itself has the capability to function like AP. Wi-Fi Direct devices, aka P2P Devices, communicate by establishing P2P Groups, which are functionally equivalent to traditional Wi-Fi infrastructure networks. The device implementing AP-like functionality in the P2P Group is referred to as the P2P Group Owner (P2P GO), and devices acting as clients are known as P2P Clients. P2P GO is sometimes referred to as Soft AP.

    Wi-Direct devices can function as 1:1 and 1:n devices. The shown topoolgy in the diagram explains the scenario of 1:1 and 1:n. In 1:1 scenario, a Wi-Fi Direct device is printing files at a printer. In 1:n scenario, a laptop is sharing files to three other Wi-Fi devices.

  • Is it possible for Group Owner to connect to Wi-Fi AP?
    image
    P2P Group Owner can also connect to AP while managing the group. Source: Devopedia.

    Only the P2P GO is allowed to cross-connect the devices in its P2P group to an external network. Wi-Fi Direct does not allow transferring the role of P2P GO within the group. If P2P GO leaves the P2P group, then the group is torn down, and has to re-established.

  • Can you explain how group formation happens?

    There are three ways of group formation: Standard, Autonomous and Persistent.

    Group formation procedure involves two phases:

    • Determination of P2P Group Owner: Two P2P devices negotiate for the role P2P Group Owner based on desire/capabilities. P2P GO role is established at formation or at an application level.
    • Provisioning of P2P Group: P2P group session is established using appropriate credentials. Wi-Fi simple configuration is used to exchange credentials.
  • Can you explain how service discovery happens?

    Service Discovery process enables Wi-Fi Direct devices to discover each other and the services they support before connecting. For example, a Wi-Fi Direct device could see all compatible devices in the area and then narrowdown the list to only devices that allow printing before displaying a list of nearby Wi-Fi Direct-enabled printers. Before establishment of a P2P Group, P2P Devices can exchange queries to discover the set of available services and, based on this, decide whether to continue the group formation or not.

    Generic Advertisement Service (GAS) as specified by 802.11u is used. GAS is a layer 2 query and response protocol implemented through the use of public action frames, that allows two non-associated 802.11 devices to exchange queries belonging to a higher layer protocol (e.g. a service discovery protocol).

  • How is security implemented in Wi-Fi Direct?

    Wi-Fi Direct devices are required to implement Wi-Fi Protected Setup (WPS) to support a secure connection with minimal user intervention. WPS is based on WPA-2 security and uses AES-CCMP as ciphering, and a randomly generated Pre-Shared Key (PSK) for mutual authentication.

  • Could you explain Wi-Fi Direct's Power Saving Mode?

    Wi-Fi Direct defines two new power saving mechanisms:

    • Opportunistic Power Save Protocol: The Opportunistic Power Save protocol (OPS) allows a P2P Group Owner to opportunistically save power when all its associated clients are sleeping. This protocol has a low implementation complexity but, given the fact that the P2P Group Owner can only save power when all its clients are sleeping, the power savings that can be achieved by the P2P Group Owner are limited.
    • Notice of Absence Protocol: The Notice of Absence (NoA) protocol allows a P2P GO to announce time intervals, referred to as absence periods, where P2P Clients are not allowed to access the channel, regardless of whether they are in power save or inactive mode. In this way, a P2P GO can autonomously decide to power down its radio to save energy.
  • What is speed of Wi-Fi Direct?

    A Wi-Fi Direct-certified device supports typical Wi-Fi speeds, which can be as high as 250 Mbps. Even at lower speeds, Wi-Fi provides plenty of throughput for transferring multimedia content with ease. The performance of a particular group of Wi-Fi Direct devices depends on whether the devices are 802.11 a, b, g, or n, as well as the particular characteristics of the devices and the physical environment.

  • Can you relate Wi-Fi Direct to Miracast?

    Miracast is a Wi-Fi display certification program announced by Wi-Fi Alliance for seamlessly transferring video between devices. The intersection of wireless connectivity and streamed audio/video content can be termed as Miracast. This solution enables seamless mirroring of entire displays across devices or sharing of any type of content that a source could display using Wi-Fi Direct.

  • Why is the design of Wi-Fi Direct based on infrastructure mode and not ad hoc mode?

    Most commercial devices are for infrastructure mode and not ad hoc mode. For easier migration and interworking with legacy devices, Wi-Fi Direct is based on infrastructure mode. Wi-Fi Direct works on the principles similar to that of Wi-Fi AP. Hence, the P2P GO is sometimes also called Soft AP..

  • Is it sufficient for only one device to be Wi-Fi Direct-certified to form a group?

    Yes. Only the P2P GO needs to be Wi-Fi Direct-certified. Other group members may be legacy Wi-Fi stations that operate in infrastructure mode. Wi-Fi Direct essentially embeds a software access point for the group owner. The soft AP provides a version of Wi-Fi Protected Setup with its push-button or PIN-based setup. Thus, group members see only an AP.

  • What are the advantages of Wi-Fi Direct?

    Wi-Fi Direct can connect multiple devices without a Wi-Fi AP. Wi-Fi Direct is portable. No Internet connection is required to transfer files between two devices. Only one device needs to be Wi-Fi Direct-certified and it can assume the role of the group owner.

  • What are the disadvantages of Wi-Fi Direct?

    Wi-Fi Direct has some limitations. Not all vendors support it. Connection has to be re-established with other devices everytime to form the group. As soon as GO leaves the group, all connections are broken and service stops. The group is formed as a star topology with the GO at the center. Group members cannot talk to each other directly.

References

  1. HSC. 2013. "Wi-Fi Direct - Overview and Features." Hughes Systique Corporation, May 6. Accessed 2018-03-05.
  2. Hoffman, Chris. 2016. "What Is Wi-Fi Direct, and How Does It Work?" How-To Geek, September 21. Accessed 2018-03-05.
  3. Kaushal D. 2016. "Android WiFi direct service discovery." Talentica Blog, December 1. Accessed 2018-03-08.
  4. Purcell, Kevin. 2010. "Wi-Fi Direct Certification: What Is It and Why Should You Care?" Notebooks.com, October 26. Accessed 2018-03-05.
  5. RF Wireless World. 2018. "WiFi Direct Basics | What is WiFi Direct." Accessed 2018-03-08.
  6. Soffar, Heba. 2016. "Wi-Fi Direct uses, advantages and disadvantages." Online Sciences, June 25. Updated 2016-11-10. Accessed 2018-03-05.
  7. Thorn, Thomas. 2014. "Wi-Fi Direct: what it is and why you should care." TechRadar, February 25. Accessed 2018-03-05.
  8. Wi-Fi.org. 2018a. "Wi-Fi Direct: Portable Wi-Fi that goes with you anywhere." Accessed 2018-03-05.
  9. Wi-Fi.org. 2018b. " How fast is Wi-Fi Direct?" Accessed 2018-03-05.
  10. Wi-Fi.org. 2018c. "How is Miracast related to Wi-Fi Direct?" Accessed 2018-03-05.
  11. Wikipedia. 2018. "Wi-Fi Direct." February 18. Accessed 2018-03-05.
  12. Šestak, Miroslav. 2017. "What's the difference between Wi-Fi and Wi-Fi Direct?" Quora, November 29. Accessed 2018-03-05.

Milestones

Oct
2010

Wi-Fi Alliance launches Wi-Fi Direct certification program. Meanwhile, Atheros, Broadcom, Intel, Ralink and Realtek announce their first products.

Oct
2011

Google announces Wi-Fi Direct support in Android 4.0.

Mar
2016

Sony, LG, Philips and X.VISION implement Wi-Fi Direct on some of their televisions.

Tags

See Also

Further Reading

  1. Wi-Fi p2p Specification.
  2. Wi-Fi Direct Equipped Cars
  3. Wi-Fi Direct News
  4. 3GPP LTE-Assisted Wi-Fi-Direct
  5. Tieu, Jimmy and Sihan Ye. 2014. "Wi-Fi Direct Services: Design and Investigation of an Emerging Wireless Technology." Master's Thesis, Department of Electrical and Information Technology, Faculty of Engineering, LTH, Lund University, June 18. Accessed 2018-03-08.

Top Contributors

Last update: 2018-11-29 07:07:21 by hemanthSK
Creation: 2018-03-04 05:52:42 by arvindpdmn

Article Stats

1291
Words
2
Chats
3
Authors
10
Edits
1
Likes
910
Hits

Cite As

Devopedia. 2018. "Wi-Fi Direct." Version 10, November 29. Accessed 2018-12-16. https://devopedia.org/wi-fi-direct
BETA V0.18