Wi-Fi Direct allows devices to directly connect and exchange data without needing an existing Wi-Fi network or hotspot. One device acts as the Group Owner to which other devices connect. Key mechanisms defined for Wi-Fi Direct include device discovery, group formation, and power management features. Wi-Fi Direct aims to simplify connectivity for use cases like printing or sharing media directly between devices.

1. Introduction to Wi-Fi Direct
Wei-Tsung Su (蘇維宗)
ellington.su@gmail.com
11/22/2012
Ubiquitous Computing and Ambient Networking Laboratory
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2. References
• Wi-Fi Alliance – Wi-Fi Direct
– http://www.wi-fi.org/discover-and-learn/wi-fi-direct
• Wi-Fi Direct Industry Whitepaper
– http://www.wi-fi.org/knowledge-center/white-papers/wi-ficertified-wi-fi-direct%E2%84%A2-personal-portable-wifi%C2%AE-technology-2010
• Wi-Fi Direct Consumer Whitepaper
– http://www.wi-fi.org/knowledge-center/white-papers/wi-ficertified-wi-fi-direct%E2%84%A2-personal-portable-wifi%C2%AE-connect-devices
• HUGHES Systique Wi-Fi Direct Whitepaper
– http://hsc.com/Portals/0/Uploads/Articles/WFD_Technology_
Whitepaper_v_1.7635035318321315728.pdf
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Ubiquitous Computing and Ambient Networking Laboratory
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3. Purpose
• Create direct connections between Wi-Fi client
devices without a traditional Wi-Fi infrastructure
network.
• For example,
– Users can print documents directly to a Wi-Fi printer
with their laptops.
– Users can cast videos directly to a Wi-Fi TV with their
smart phones.
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4. How Wi-Fi Direct Works?
Group
Group
GO
GO
Connection
One-to-one configuration
One-to-many configuration
As long as one device in a connection is
Wi-Fi Direct-certified, you can connect all
devices without a Wi-Fi home network or
hotspot.
GO is short for Group Owner
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5. Key Mechanisms
Key Mechanisms
Mandatory
Device Discovery
X
Service Discovery
Optional
X
Group Formation
X
Invitation
X
Client Discovery
X
Power Management
P2P-PS and P2P-WMM-PS
X
Notice of Absence
X
Opportunistic Power Save
X
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Ubiquitous Computing and Ambient Networking Laboratory
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6. Device Discovery
• Identify other Wi-Fi Direct devices and establish
a connection
– If the target is not in a Group, a new Group is formed
• GO is negotiated.
– If the target is already part of a Group, the searching
device may attempt to join the existing Group.
• Wi-Fi Protected Setup (WPS) is used to obtain
credentials and authenticate the searching
device.
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Ubiquitous Computing and Ambient Networking Laboratory
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7. Service Discovery (Optional)
• Advertise the higher layer applications to other
Wi-Fi Direct devices (even before a connection is
formed).
– For example, Wi-Fi printer can advertise its printing
services to other Wi-Fi Devices
• Implementation is vender-specific.
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8. Group Formation
• Once a Wi-Fi Direct connection is established between two Wi-Fi Direct
devices, a Group is formed.
• However, a Group may be created by a single Wi-Fi Direct device
– Required when connecting a legacy device
– Desirable when creating a Group to offer a specific service (e.g. Internet
connection sharing.)
• Once a Group is formed, other devices can join this Group as join a AP.
• A Group can be
– temporary Group (single instance)
– Persistent Group (multiple, recurring use)
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Ubiquitous Computing and Ambient Networking Laboratory
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9. Invitation (Optional)
• After a Group is formed,
a Wi-Fi Direct device may
invite another Wi-Fi
Direct device to join the
Group.
• The decision of whether
or not to accept an
invitation is left to the
invited Wi-Fi Direct
device.
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Ubiquitous Computing and Ambient Networking Laboratory
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10. Client Discovery
• Enabling a Wi-Fi Direct device to discover which
Wi-Fi Direct devices are in an existing Group.
• Locate and connect to a specific device or device
type.
– For example, a camera can query to see if any Wi-Fi
devices are printers in a Group.
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11. Power Management
• P2P-PS and P2P-WMM-PS
– based on Wi-Fi Power Save (PS) and WMM-PS
• Notice of Absence
– Signal a planned absence
• Opportunistic Power Save
– Save power by entering doze state
– Group owner is available on a periodic basis.
• If legacy devices are present, these power
management functions cannot be employed.
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12. Important Capabilities
Important Capabilities
Mandatory
Optional
Persistent Group
X
Concurrent Connection
X
Multiple Groups
X
Cross-connection
X
Managed Device
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13. Persistent Group (Optional)
• Persistent Group may be restarted without
provisioning, eliminating the need to repeat
tasks such as entering a WPS PIN.
• Persistent Group are invoked using Invitation
mechanism. That is, all Wi-Fi Direct devices must
support Invitation in a Persistent Group.
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14. Concurrent Connection (Optional)
• Concurrent connection
– Concurrent devices can be in a group while maintaining a
WLAN infrastructure connection at the same time.
• Multiple group
– Join multiple Groups
• Cross-connection
– Provide infrastructure access to other devices in the Group
– Concurrent operation requires support for multiple and
distinct MAC entities.
• One for operation as a WLAN-STA
• One for operation as a Wi-Fi Direct device
• Implementation is vender-specific
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15. Managed Environments (Optional)
• A Wi-Fi AP may implement capabilities that allow
it to manage Wi-Fi Direct devices for efficiency
and security issues. For example,
– enforce Wi-Fi Direct devices do not use 802.11b for
data and management frames.
– de-authentication any Wi-Fi Direct device from the
infrastructure network for our-of-policy behavior.
• For example, all client devices that Cross-connection is not
allowed if they attempt to access infrastructure network
resources.
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16. Wi-Fi Direct Certification Program
• Wi-Fi CERTIFIED Wi-Fi Direct devices must
implement Wi-Fi Peer-to-Peer technology (P2P).
• Wi-Fi CERTIFIED Wi-Fi Direct devices must pass the
following certification tests
– Baseline Wi-Fi certification tests
• At least 802.11g as well as WPA2-Personal
– Wi-Fi Multimedia (WMM) and Wi-Fi Protected Setup
(WPS) certification tests
• WMM and WPS are optional Wi-Fi Alliance certification, but
both are mandatory for Wi-Fi Direct certification
– All mandatory certification tests
– Optional features certification tests. (tested if
implemented.)
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