DEVICE-TO-DEVICE COMMUNICATION WITH WI-FI DIRECT : OVERVIEW & EXPERIMENTATION

Speaker : Liang-Lin Yan

Advisor : Dr. Ho-Ting Wu

2014/12/2

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OUTLINE IntroductionD2D Communication Wi-Fi Direct Experimental Evaluation Conclusion References

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INTRODUCTION The IEEE 802.11 standard , has become one of the most

common ways to access the Internet.

Given the wide adoption of Wi-Fi in many kinds of devices, a natural way for the technology to progress is to target device-to-device connectivity, i.e. without requiring the presence of an Access Point (AP)

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INTRODUCTION Direct device to device connectivity was already

possible in the original IEEE 802.11 standard by means of the ad hoc mode of operation.

There have several drawbacks when facing nowadays requirements, e.g. lack of efficient power saving support or extended QoS capabilities.

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INTRODUCTION The Wi-Fi Direct technology approach to enhance device

to device connectivity. Instead of leveraging the ad-hoc mode of operation.

Wi-Fi Direct builds upon the successful IEEE 802.11 infrastructure mode and lets devices negotiate who will take over the AP-like functionalities.

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INTRODUCTION

Legacy Wi-Fi devices may seamlessly connect to Wi-Fi Direct devices and immediately inherits all the enhanced QoS, power saving, and security mechanisms developed for the Wi-Fi infrastructure mode in the past years.

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DEVICE-TO-DEVICE COMMUNICATION現有技術的資料與控制訊號皆須透過核心網路傳遞，將帶來核心網路壅塞的問題，因此，不須透過基地台的直接通訊 (Direct Communication)技術便逐漸受到重視。

發展支援不同通訊模式、跨載具、跨系統的整合通訊平台，將是裝置與裝置間通訊 (Device-to-Device Communications, D2D)技術發展的挑戰。

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DEVICE-TO-DEVICE COMMUNICATION

進行 D2D通訊行為的成員通常由至少兩個以上的相鄰終端裝置所組成，並啟動相同的應用服務，如社交互動、合作遊戲、多螢控制、 Push-to-Talk等，透過裝置搜尋 (Discovery)、配對 (Pairing)等程序建立連線。

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DEVICE-TO-DEVICE COMMUNICATION單向、雙向的訊息透過虛擬通道，在呼叫端與被呼叫端間傳遞。

虛擬通道類似 Bus的概念，負責訊息的傳送與接收、辨認不同的來源與處理程序，並將訊息送往正確的目的地。

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DEVICE-TO-DEVICE COMMUNICATION

D2D conmmunication 示意圖

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DEVICE-TO-DEVICE COMMUNICATION開發商僅須專注於開發更高階層的應用功能及情境

D2D鄰近通訊的技術平台可分為 Peer :

負責應用程序層級的交流 Daemon:

實質處理底層各種訊息的運作細節

兩者以相對應的技術層次 (Layer)交互溝通

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WI-FI DIRECT :ARCHITECTURE Wi-Fi Direct devices, formally known as P2P Devices,

communicate by establishing P2P Groups.

P2P Group Owner: the device implementing AP-like functionality in the P2P Group

P2P Clients: devices acting as clients

When two P2P devices discover each other they negotiate their roles to establish a P2P Group.

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WI-FI DIRECT :ARCHITECTURE P2P Group is established, other P2P Clients can join the

group as in a traditional Wi-Fi network.

As long as devices are not 802.11b only devices and support the required security mechanisms.

Legacy devices do not formally belong to the P2P Group, but they simply “see” the P2P GO as a traditional AP.

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WI-FI DIRECT

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WI-FI DIRECT :GROUP OWNER(GO) Announce itself through beacons

Support power saving services for its associated clients

Run a DHCP server to provide clients with IP addresses

Wi-Fi-Direct does not allow the transfer of GO role within a group and if the GO leaves the group, the group is torn down and has to be re-established

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WI-FI DIRECT :GROUP FORMATION Standard

P2P devices have to negotiate the role of P2P GO

AutonomousA P2P device may autonomously create a P2P Group

PersistentThere is some pre-shared security information

available

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GROUP FORMATION: STANDARD Wi-Fi Direct devices usually start Wi-Fi scan (active or

passive) to discover existent P2P Groups and Wi-Fi networks

After this scan, a new algorithm is executed

1. A P2P Device selects one of the so-called Social channels, namely channels 1, 6 or 11 in the 2.4 GHz band, as its Listen channel.

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GROUP FORMATION: STANDARD2. A P2P Device alternates between two states

Search state: the device performs active scanning by sending Probe Requests in each of the social channels

Listen state: the device listens for Probe Requests in its listen channel to respond with Probe Responses

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GROUP FORMATION: STANDARD GO Negotiation

Once the two P2P devices have found each other, they start the GO Negotiation phase

Implemented using a three-way handshake, namely GO Negotiation Request/Response/ConfirmationThe two devices agree on which device will act as P2P

GO and on the channel where the group will operate, which can be in the 2.4 GHz or 5 GHz bands.

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GROUP FORMATION: STANDARD WPS (Wi-Fi Protected Setup) Provisioning

Establishment of a secure communication using Wi-Fi Protected Setup

Address Config.

A DHCP exchange to set up the IP configuration

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GROUP FORMATION: STANDARD

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GROUP FORMATION: AUTONOMOUS A P2P device may autonomously create a P2P Group,

where it immediately becomes the P2P GO, by sitting on a channel and starting to beacon.

Other devices can discover the established group using traditional scanning mechanisms, and then directly proceed with the WPS Provisioning and Address Configuration phases.

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GROUP FORMATION: AUTONOMOUS

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GROUP FORMATION: PERSISTENT P2P devices can declare a group as persistent, by using a

flag in the P2P Capabilities attribute present in Beacon frames, Probe Responses and GO negotiation frames.

The devices forming the group store network credentials and the assigned P2P GO and Client roles for subsequent re-instantiations of the P2P group.

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GROUP FORMATION: PERSISTENT

After the Discovery phase, if a P2P device recognizes to have formed a persistent group with the corresponding peer in the past, any of the two P2P devices can use the Invitation Procedure (a two-way handshake) to quickly re-instantiations the group.

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GROUP FORMATION: PERSISTENT

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WI-FI DIRECT :LAYER TWO SERVICE DISCOVERY

A salient feature of Wi-Fi Direct is the ability to support service discovery at the link layer.

Prior to the 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.

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WI-FI DIRECT :LAYER TWO SERVICE DISCOVERY

In order to service discovery queries generated by a higher layer protocol, e.g., UPnP, are transported at the link layer using the Generic Advertisement Protocol (GAS) specified by 802.11u.

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WI-FI DIRECT :SECURITY Wi-Fi Direct devices are required to implement Wi-Fi

Protected Setup (WPS) to support a secure connection with minimal user intervention.

WPS allows to establish a secure connection Introducing a PIN in the P2P Client Pushing a button in the two P2P Devices.

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WI-FI DIRECT :SECURITY

Registrar (by GO) is in charge of generating and issuing the network credentials to the Enrollee (by clients).

The Enrollee disassociates and reconnects using its new authentication credentials.

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WI-FI DIRECT :POWER SAVING Using Wi-Fi Direct, battery-constrained devices may

typically act as P2P GO and therefore energy efficiency is of capital importance.

Wi-Fi Direct defines two new power saving mechanisms for APs: 1. Opportunistic Power Save protocol

2. Notice of Absence (NoA) protocol

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EXPERIMENTAL EVALUATION

1. To analyze the time required to form a P2P group for the three cases described in the previous section.

2. To quantify the achievable performance trade-offs using Wi-Fi Direct and compare them against legacy operation.

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TESTBED SETUP Deploy a testbed consisting of two nodes in an office

environment, where different WLANs could be detected, and perform the experiments during working.

The nodes are two laptops equipped with an 802.11a/b/g D-Link PCMCIA card with an Atheros chipset, running Linux and the mac80211/ath5k driver.

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TESTBED SETUP Use an open source implementation of Wi-Fi Direct,

which builds on the widely deployed wpa_supplicant software, and extend it to implement the Notice of Absence (NoA) protocol.

Implement NoA as this mechanism provides the AP with the tightest control and should provide the maximum energy savings.

Throughout experiments always pre-provision the devices with a WPS PIN, to support automatized execution.

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GROUP FORMATION DELAY

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ENERGY-EFFICIENT OPERATION

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CONCLUSION Wi-Fi has become a predominant way to access the

Internet wirelessly, it is now embracing the challenge of becoming pervasive also in direct device to device communications.

Wi-Fi Alliance has recently developed the Wi-Fi Direct technology that builds upon the Wi-Fi infrastructure mode to enable direct device to device connectivity.

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REGARDING FUTURE RESEARCH DIRECTIONS

1. The NoA protocol could also be re-used to virtualize the roles of P2P GO/Client over multiple concurrent P2P Groups.

2. Concurrent operation together with the dynamic nature of the P2P GO/Client roles could be used to improve performance in dense environments, for instance by means of dynamic relays.

3. If Wi-Fi Direct becomes a widespread technology as expected, it faces the challenge of improving coexistence and reducing interference with other unlicensed devices.

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REFERENCES D. Camps-Mur, A. Garcia-Saavedra, and P. Serrano,

"Device-to-device communications with Wi-Fi Direct: overview and experimentation," IEEE Wireless Communications, vol. 20, no. 3, Jun. 2013.

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Thanks for your listening!