Introduction to Wi-Fi Direct

Introduction to Wi-Fi Direct

Wei-Tsung Su (蘇維宗)

[email protected]

11/22/2012 Ubiquitous Computing and Ambient Networking Laboratory Page : 1

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-fi-certified-wi-fi-direct%E2%84%A2-personal-portable-wi-fi%C2%AE-technology-2010

• Wi-Fi Direct Consumer Whitepaper

– http://www.wi-fi.org/knowledge-center/white-papers/wi-fi-certified-wi-fi-direct%E2%84%A2-personal-portable-wi-fi%C2%AE-connect-devices

• HUGHES Systique Wi-Fi Direct Whitepaper

– http://hsc.com/Portals/0/Uploads/Articles/WFD_Technology_Whitepaper_v_1.7635035318321315728.pdf


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.


How Wi-Fi Direct Works?


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.

Group

Connection

Group

GOGO

GO is short for Group Owner

Key Mechanisms

Key Mechanisms Mandatory Optional

Device Discovery X

Service Discovery 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


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.


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.


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)


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.


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.


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.


Important Capabilities

Important Capabilities Mandatory Optional

Persistent Group X

Concurrent Connection X

Multiple Groups X

Cross-connection X

Managed Device X


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.


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


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.


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.)
